All of Edexcel PHYSICS Paper 1 in 45 minutes - GCSE Science Revision

00:39:21
https://www.youtube.com/watch?v=Dvpp5Ja0gfY

Sintesi

TLDRThe video is an extensive revision for the Edexcel GCS Physics paper 1, addressing key topics relevant to combined and separate physics. It emphasizes the importance of prefixes for measurement units, detailed explanations of forces and their vector representations, Newton's laws of motion, energy calculations through equations, wave properties in various mediums, and radioactivity types. Moreover, the video discusses the electromagnetic spectrum, lens behavior, and fundamental astrophysics concepts, including the Big Bang Theory. Practical illustrations and contextual examples seek to enhance comprehension for exam preparation. The structure encourages learners to grasp essential physics principles effectively and is suitable for both higher and foundation tiers.

Punti di forza

  • 📐 Measurement units like meters and seconds are crucial in physics.
  • 📏 Prefixes help simplify large or small numbers (e.g., 1 km = 1000 m).
  • 💬 Forces are vector quantities; balance leads to constant motion.
  • ⚖️ Gravitational potential energy is calculated using mass, height, and gravity.
  • 🔄 Newton's laws explain motion changes under force influence.
  • 🌀 Waves are characterized by their amplitude, wavelength, and frequency.
  • 🕯️ Understanding electromagnetic waves is key for tech applications.
  • 🌠 The Big Bang Theory provides insights into the universe's origin.
  • ⚙️ Energy conservation is vital in closed systems; energy transfers form but is not lost.
  • 🚗 Momentum conservation helps explain collisions.

Linea temporale

  • 00:00:00 - 00:05:00

    The video introduces the key concepts for Ed Excel GCS physics paper 1, covering essential topics such as motion, forces, energy conservation, and more. It emphasizes the importance of prefixes in measurements, the significance of vectors in representing forces, and how scalar quantities are different from vector quantities.

  • 00:05:00 - 00:10:00

    This section elaborates on acceleration, defining it as the change in speed over time. It discusses the distinction between positive and negative acceleration, illustrating how to interpret velocity-time graphs to derive information about an object's motion and distance traveled.

  • 00:10:00 - 00:15:00

    Newton's laws of motion are covered, explaining the concepts of resultant forces, inertia, and how they relate to the acceleration of objects. It focuses on practical implications and examples of conducting experiments to illustrate these laws.

  • 00:15:00 - 00:20:00

    Momentum is introduced as a concept that is linked to Newton's laws. The video details how to calculate momentum and explains the conservation of momentum in collisions, including the importance of directions and updating variables appropriately during calculations.

  • 00:20:00 - 00:25:00

    This section explains energy conservation, types of energy, and equations for different forms, demonstrating energy transfer in various systems. The importance of closed systems in maintaining energy balance is also discussed, including practical examples like roller coasters.

  • 00:25:00 - 00:30:00

    Waves and their properties are explored, distinguishing between longitudinal and transverse waves. It discusses how frequency, amplitude, and wavelength relate to wave behavior, as well as real-world applications like sound waves, sonar, and ultrasounds.

  • 00:30:00 - 00:39:21

    The final sections delve into radioactivity, nuclear reactions, and astrophysics. Key concepts include the nature of radiation, half-life calculations, and the fusion and fission processes in stars. It emphasizes the implications of these processes in the context of cosmic events and the universe's expansion.

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Video Domande e Risposte

  • What are the main topics covered in the video?

    The video covers motion and forces, conservation of energy, waves, electromagnetism, radioactivity, and astronomy.

  • What is the unit for force?

    The unit for force is Newtons (N).

  • How do you calculate gravitational potential energy?

    Gravitational potential energy (GPE) is calculated using the formula GPE = mass (kg) * gravitational field strength (N/kg) * height (m).

  • What is the difference between speed and velocity?

    Speed is a scalar quantity that refers to how fast something is moving, while velocity is a vector quantity that includes both speed and direction.

  • What are Newton's three laws of motion?

    Newton's first law states that an object at rest stays at rest unless acted upon by a net force. His second law states that F = ma (force equals mass times acceleration). His third law states that for every action, there is an equal and opposite reaction.

  • What is momentum?

    Momentum is the product of mass and velocity (p = mv) and is a vector quantity.

  • What types of electromagnetic waves are mentioned?

    The electromagnetic waves discussed include radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

  • What does the term 'radioactivity' mean?

    Radioactivity refers to the process in which unstable atomic nuclei lose energy by emitting radiation.

  • How is energy conserved in a closed system?

    In a closed system, energy cannot be created or destroyed; it can only be transferred between forms.

  • What is the significance of the Big Bang Theory?

    The Big Bang Theory explains the origin of the universe and indicates that galaxies are expanding, which is evidenced by redshift observations.

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Scorrimento automatico:
  • 00:00:00
    let's see how quickly we can cover
  • 00:00:01
    everything you need to know for Ed Exel
  • 00:00:02
    GCS physics paper 1 this is good for
  • 00:00:05
    higher Own Foundation Tier double
  • 00:00:06
    combined and triple separate physics
  • 00:00:09
    that's topics 1 to 7 key Concepts motion
  • 00:00:12
    and forces conservation of energy wave
  • 00:00:13
    lighten the EM spectrum radioactivity
  • 00:00:16
    and astronomy wow we better get cracking
  • 00:00:18
    as we're going to have to gun it pause
  • 00:00:20
    the video if you need a bit more time to
  • 00:00:21
    get your head around something you see
  • 00:00:23
    let's go every measurement or quantity
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    has a unit meters for distance seconds
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    for time Etc but if it's a really big
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    big or really small number we can put a
  • 00:00:31
    prefix in front so 1,000 M we can write
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    as 1 kilom 1 km for short prefixes
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    generally go up or down in thousands
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    times 1,000 divide by a th000 apart from
  • 00:00:43
    centimeters and decimeters here are the
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    ones that you need to know to convert
  • 00:00:47
    units you always need to think do I want
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    a bigger number multiplied by the
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    conversion factor or a smaller number in
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    that case you divide by the conversion
  • 00:00:55
    factor for example what's 5 micrometers
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    in meters it's a th000 to get to
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    millimet and another th000 to get to
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    meters so is it 5 * 1,000 * 1,000 no
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    because that would give us 5 million M
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    it's 5 divided by a th000 divided by a
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    th000 again or 5 divided by a million as
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    this is a very small number now we can
  • 00:01:14
    write it in standard form that would be
  • 00:01:16
    5 * 10- 6 that Min - 6 tells us that
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    we've divided by 10 six times which is
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    the same as dividing by a million
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    anything bigger than a meter is going to
  • 00:01:26
    be a positive power on that 10 here are
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    the other prefixes in standard form too
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    a force is any push or pull forces can
  • 00:01:35
    be contact forces that's when objects
  • 00:01:36
    are physically touching like when you
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    push a door or they can be non- contct
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    like magnetism electrostatic forces and
  • 00:01:43
    gravity This Is A New Concept in gcsc
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    physics and shocker it's a silly one
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    because even contact forces are due to
  • 00:01:49
    the electrostatic repulsion between
  • 00:01:51
    electrons in your skin and the door for
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    example but whatever technically pushing
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    a door involves a normal contact force
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    while other contact forces could be
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    friction air resistance and tension the
  • 00:02:02
    important thing is that we can represent
  • 00:02:04
    forces with vectors that is an arrow
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    that shows the direction and magnetude
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    of the force the magnitude is the size
  • 00:02:10
    of the force and that's indicated by the
  • 00:02:11
    length of the arrow if two forces act on
  • 00:02:14
    an object there's a resultant Force we
  • 00:02:17
    find this by technically adding the
  • 00:02:18
    vectors however if they're going in
  • 00:02:20
    opposite directions one must be negative
  • 00:02:22
    so in this case the resultant force
  • 00:02:24
    would be 3 Newtons to the right and
  • 00:02:26
    that's positive if we've decided that
  • 00:02:28
    positive is in the right direction if
  • 00:02:30
    vectors are at right angles to each
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    other you use Pythagoras to find the
  • 00:02:34
    resultant this works because you can
  • 00:02:36
    make a triangle by moving one of the
  • 00:02:38
    forces you could also be expected to use
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    trig that's soccer TOA to find either
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    one of these angles chances is going to
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    be tan you use if any if forces are
  • 00:02:46
    balanced that is they add up to zero
  • 00:02:48
    that means that the object will not
  • 00:02:50
    accelerate it won't change velocity no
  • 00:02:53
    that doesn't necessarily mean it's not
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    moving it just stays at a constant
  • 00:02:57
    velocity and that could be zero meters
  • 00:02:59
    per second of course this is Newton's
  • 00:03:00
    first law of motion by the way more on
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    those in a bit if a measurement of
  • 00:03:04
    quantity just has magnitude but no
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    direction it's not a vector but it's
  • 00:03:08
    called a scalar instead here are some
  • 00:03:09
    examples of both note that displacement
  • 00:03:12
    is distance traveled with a direction
  • 00:03:14
    while similarly velocity is the vector
  • 00:03:16
    form of speed weight is another name for
  • 00:03:19
    the force due to gravity that acts on an
  • 00:03:21
    object it's calculated by multiplying
  • 00:03:22
    the mass in kilograms by gravitational
  • 00:03:24
    field strength or G which here on Earth
  • 00:03:26
    is 9.8 Newtons per kilog sometimes we
  • 00:03:29
    just round up to 10 though you'll be
  • 00:03:31
    told which to use in a question that
  • 00:03:32
    means that 1 kg of Mass on Earth has a
  • 00:03:34
    weight of 10 Newtons now if you hold an
  • 00:03:37
    object up with your hand you must be
  • 00:03:39
    pushing up with a force that is equal to
  • 00:03:41
    its weight in order for the forces to be
  • 00:03:43
    balanced and so it doesn't accelerate
  • 00:03:45
    however that means that if you lift it
  • 00:03:47
    upwards at a constant speed that's also
  • 00:03:49
    true that's something that people often
  • 00:03:51
    forget to lift something at a constant
  • 00:03:53
    speed you must be lifting with a force
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    that's the same as the weight we can
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    therefore then calculate the energy that
  • 00:03:59
    is used to lift this object using the
  • 00:04:01
    equation for work done that's work done
  • 00:04:04
    equals force time distance moved work
  • 00:04:06
    done is just a fancy term for energy
  • 00:04:08
    transferred by a force this equation is
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    true for any situation but in this case
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    the force is the weight and the distance
  • 00:04:15
    is the height so we could say the gain
  • 00:04:17
    in energy is equal to mass * G * H does
  • 00:04:21
    that look familiar it should because
  • 00:04:22
    that's the exact same equation for
  • 00:04:24
    calculating gravitational potential
  • 00:04:25
    energy that's GP gained to be precise
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    back to double speed and velocity are
  • 00:04:30
    measured in me/ second while velocity
  • 00:04:33
    also has Direction so it could be
  • 00:04:35
    positive or negative or up and down left
  • 00:04:37
    and right here are some typical speeds
  • 00:04:39
    for when you're traveling of course
  • 00:04:40
    speed and velocity are calculated by
  • 00:04:42
    distance or displacement over time if
  • 00:04:44
    you have a distance time graph the
  • 00:04:46
    gradient of the graph gives you the
  • 00:04:47
    speed or velocity if it's a curve just
  • 00:04:49
    draw a tangent at the point you need to
  • 00:04:51
    and find its gradient a speed or
  • 00:04:54
    velocity time graph can give you even
  • 00:04:55
    more information this time the gradient
  • 00:04:57
    gives you change in speed divided by
  • 00:04:59
    time which is acceleration here's the
  • 00:05:01
    equation two the unit of acceleration is
  • 00:05:03
    m/s squared and it tells you how quickly
  • 00:05:05
    speed is changing if it's a negative
  • 00:05:07
    gradient heading to zero that means the
  • 00:05:09
    object is decelerating slowing down
  • 00:05:12
    however this graph can also go into
  • 00:05:14
    negative values for example when a ball
  • 00:05:16
    is thrown upward and comes back down in
  • 00:05:18
    that case the velocity starts positive
  • 00:05:20
    and fast but decreases to zero when it
  • 00:05:23
    reaches the top where it then turns
  • 00:05:25
    around so the velocity becomes more
  • 00:05:27
    negative as it falls in that this graph
  • 00:05:30
    has a constant negative gradient gravity
  • 00:05:32
    is accelerating it downwards at a
  • 00:05:35
    constant rate even though its direction
  • 00:05:37
    changes what you find is that for any
  • 00:05:39
    object that's falling its acceleration
  • 00:05:41
    is 9.8 m/s squared the same as
  • 00:05:45
    gravitational field strength because
  • 00:05:46
    they are the same thing a velocity time
  • 00:05:48
    graph can also give you the distance
  • 00:05:50
    traveled you get that by calculating the
  • 00:05:52
    area under the graph any area under 0
  • 00:05:55
    m/s counts as negative displacement by
  • 00:05:57
    the way thus where the area of both
  • 00:05:59
    these triangles in this graph adds up to
  • 00:06:01
    zero that makes sense though doesn't it
  • 00:06:03
    seeing that it's gone back from whence
  • 00:06:04
    it came I.E your hand suat or Newton's
  • 00:06:08
    equations of motion are a way of
  • 00:06:09
    predicting what an object will do if
  • 00:06:11
    it's accelerating s is displacement U is
  • 00:06:14
    initial velocity V is final velocity a
  • 00:06:16
    is acceleration and T is time U is zero
  • 00:06:19
    if it starts at rest V equals Zer if an
  • 00:06:22
    object is moving to begin with but then
  • 00:06:24
    decelerates to a standstill for objects
  • 00:06:26
    falling a is the same as G that's 9.8
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    m/s squared for any question involving
  • 00:06:31
    one of these equations you write down
  • 00:06:33
    your variables put a question mark next
  • 00:06:35
    to what you're trying to find and put
  • 00:06:36
    the values next to the other three that
  • 00:06:38
    you've been given you can ignore the
  • 00:06:40
    fifth unused variable depending on what
  • 00:06:42
    data you're given you pick the correct
  • 00:06:44
    equation with the four variables in
  • 00:06:47
    rearrange it if necessary then just plug
  • 00:06:49
    in your numbers we already know that
  • 00:06:50
    Newton's first law is this when there's
  • 00:06:53
    no resultant Force an object's motion is
  • 00:06:55
    constant in other words no change in
  • 00:06:57
    velocity that could be because there's
  • 00:06:58
    no forces all the forces are balanced by
  • 00:07:02
    the way inertia is the term we use to
  • 00:07:04
    describe the tendency for an object's
  • 00:07:06
    motion to stay constant unless acted on
  • 00:07:08
    by a resultant Force Newton's Second Law
  • 00:07:11
    involves unbalanced forces that is there
  • 00:07:14
    is a resultant Force this is equal to ma
  • 00:07:17
    masstimes acceleration that's all
  • 00:07:19
    Newton's second law is f equals ma only
  • 00:07:21
    one of these can be true in any
  • 00:07:23
    situation there's either no resultant
  • 00:07:26
    force or there is we can prove Newton's
  • 00:07:28
    second law by do in a practical we use a
  • 00:07:31
    trolley on a track being pulled by the
  • 00:07:32
    weight of masses hanging over a pulley
  • 00:07:34
    on the end we can use light Gates photo
  • 00:07:36
    gates to measure the acceleration
  • 00:07:38
    between two points then change the
  • 00:07:40
    weight on the string just remember that
  • 00:07:42
    whatever Mass you take off the hanger
  • 00:07:44
    must go on the trolley itself as the
  • 00:07:47
    force is accelerating both the trolley
  • 00:07:49
    and the masses themselves we draw a
  • 00:07:51
    graph of force against acceleration and
  • 00:07:52
    it should be a straight line through the
  • 00:07:54
    origin proving the proportional
  • 00:07:56
    relationship between F and a the
  • 00:07:57
    gradient should give you the total mass
  • 00:07:59
    of the trolley and slotted masses
  • 00:08:01
    Newton's third law however is always
  • 00:08:03
    true and this is the one that people get
  • 00:08:05
    confused about understandably for every
  • 00:08:07
    action of force there is an equal and
  • 00:08:09
    opposite reaction force but this is not
  • 00:08:12
    referring to balanced forces it's all
  • 00:08:14
    about perspective when we think about
  • 00:08:16
    the first two laws we only really
  • 00:08:18
    consider the object itself for example
  • 00:08:20
    the force pulling downwards on the ball
  • 00:08:21
    is its weight even if there is air
  • 00:08:23
    resistance there's a resultant Force
  • 00:08:25
    downwards however if you zoom out and
  • 00:08:27
    think about the Earth too
  • 00:08:30
    well we know that the Earth is pulling
  • 00:08:31
    down the ball but Newton's third law
  • 00:08:34
    says the complete opposite is true as
  • 00:08:36
    well the ball is also pulling the Earth
  • 00:08:40
    up now the Earth is so massive that it
  • 00:08:42
    doesn't really have an effect but it's
  • 00:08:44
    still true nevertheless another example
  • 00:08:47
    if you have two ice skaters if the guy
  • 00:08:49
    skater pushes on the girl skater there's
  • 00:08:51
    an equal and opposite reaction force
  • 00:08:53
    pushing back on him too that's why they
  • 00:08:56
    both move away from where they were the
  • 00:08:58
    overall stopping distance for a car is a
  • 00:09:00
    result of the thinking distance that's
  • 00:09:02
    how far you go before you react to
  • 00:09:04
    seeing the Bunny and the breaking
  • 00:09:06
    distance after you slammed on the brakes
  • 00:09:08
    if you double your speed you double your
  • 00:09:10
    thinking distance because you travel
  • 00:09:12
    twice as far in the time it takes for
  • 00:09:13
    you to react makes sense however
  • 00:09:16
    doubling your speed quadruples your
  • 00:09:18
    braking distance because your car needs
  • 00:09:20
    to lose all of its kinetic energy which
  • 00:09:22
    is equal to half MV s well that means
  • 00:09:25
    that if you double the V * 2^ 2 is * 4
  • 00:09:29
    four if you triple your speed kinetic
  • 00:09:31
    energy goes up by time 9 so that means
  • 00:09:34
    so does your breaking distance other
  • 00:09:36
    factors that affect thinking distance
  • 00:09:37
    are distractions alcohol drugs whereas
  • 00:09:40
    braking distance can be affected by the
  • 00:09:42
    condition of your brakes the tires the
  • 00:09:44
    road the weather Etc the faster you go
  • 00:09:47
    the more momentum you also have momentum
  • 00:09:50
    is similar to inertia you can think of
  • 00:09:52
    it as being a measure of how hard it is
  • 00:09:53
    to get something to stop here's the
  • 00:09:55
    equation momentum is equal to masstimes
  • 00:09:57
    Velocity the unit therefore is kilogram
  • 00:10:00
    m/s momentum is a vector which means you
  • 00:10:02
    have negative momentum if your velocity
  • 00:10:05
    is negative in a collision kinetic
  • 00:10:07
    energy isn't always conserved but total
  • 00:10:09
    momentum always is that means whatever
  • 00:10:12
    the total momentum of the objects was
  • 00:10:14
    before there must be the same total
  • 00:10:16
    momentum afterwards as well calculations
  • 00:10:19
    on this can be tricky but you just have
  • 00:10:20
    to be careful with your pluses and
  • 00:10:22
    minuses you write down M1 U1 if there's
  • 00:10:25
    just one object moving to begin with
  • 00:10:27
    remember U from suat we can use it here
  • 00:10:29
    too and on M2 U2 if there's a second
  • 00:10:32
    object moving too this then is the total
  • 00:10:34
    momentum before the Collision before the
  • 00:10:35
    event this could also be zero if
  • 00:10:38
    nothing's moving to begin with say a
  • 00:10:39
    cannon about to fire then all we have to
  • 00:10:41
    say is that this is equal to the total
  • 00:10:43
    momentum afterwards M1 V1 for one object
  • 00:10:46
    plus M2 V2 if there's a second object
  • 00:10:48
    moving too if they've coupled together
  • 00:10:50
    we just say m * V where m is the total
  • 00:10:53
    mass of the two then all you have to do
  • 00:10:54
    is pop your numbers in making sure that
  • 00:10:56
    everything traveling to the left say has
  • 00:10:58
    a negative velocity and you'll be left
  • 00:11:00
    with one unknown rearrange to find it
  • 00:11:03
    you get your answer incidentally in the
  • 00:11:05
    case of the Cannon as there's zero to
  • 00:11:07
    momentum before the same must be true
  • 00:11:09
    after too even though the cannon ball is
  • 00:11:11
    moving that must mean the cannon has the
  • 00:11:14
    same momentum but in the opposite
  • 00:11:16
    direction so they still add up to zero
  • 00:11:19
    this is an example of recoil just for
  • 00:11:21
    triple force and momentum are closely
  • 00:11:23
    linked Newton's second law says that FAL
  • 00:11:25
    ma but we also know that a is equal to
  • 00:11:27
    delta v/ T so actually
  • 00:11:29
    it's also true that force is equal to
  • 00:11:31
    change in momentum over time or we can
  • 00:11:34
    say the rate of change of momentum the
  • 00:11:36
    shorter the time taken for momentum to
  • 00:11:38
    change the bigger the force needed or
  • 00:11:41
    felt that's why we use seat belts
  • 00:11:43
    airbags and crumble zones in cars your
  • 00:11:45
    change in momentum is the same when you
  • 00:11:47
    use them but they increase the time
  • 00:11:49
    taken for this to happen so a smaller
  • 00:11:51
    force is felt you're more likely to
  • 00:11:53
    survive it's just two ways of looking at
  • 00:11:56
    forces the bigger the force the faster
  • 00:11:58
    the acceleration or deceleration ation
  • 00:11:59
    and so that also means the fast the
  • 00:12:01
    momentum changes too energy isn't
  • 00:12:03
    something you can hold in your hand it's
  • 00:12:06
    just an idea it's a number that tells us
  • 00:12:08
    what will happen when objects interact
  • 00:12:10
    in what we call a system total energy in
  • 00:12:13
    any interaction is always conserved
  • 00:12:16
    energy cannot be created or destroyed
  • 00:12:19
    now there is a small caveat with that as
  • 00:12:21
    energy can be turned into matter Mass
  • 00:12:23
    but it's still technically true the
  • 00:12:25
    whole Mass 2 energy thing is only
  • 00:12:27
    important for triple people in topic
  • 00:12:28
    four when it comes to nuclear fision and
  • 00:12:30
    fusion there are what some people call
  • 00:12:32
    different stores of energy normal people
  • 00:12:34
    just say types of energy but these days
  • 00:12:36
    the exam boards are obsessed with the
  • 00:12:38
    word stores so that's what we're going
  • 00:12:40
    to have to use the energy in these
  • 00:12:42
    energy stores changes when objects
  • 00:12:45
    interact energy is measured in Jewels an
  • 00:12:48
    object can have energy in the following
  • 00:12:50
    stores kinetic energy we calculate it
  • 00:12:53
    with e = half mv^ 2 half time mass in
  • 00:12:57
    kilog speed or velocity squared the
  • 00:13:00
    faster an object goes the more kinetic
  • 00:13:02
    energy it has gravitational potential
  • 00:13:04
    energy or GP for short we calculate that
  • 00:13:06
    byal MGH that's masstimes gravitational
  • 00:13:10
    field strength either 10 or 9.8 in
  • 00:13:13
    Newtons per kilogram you'll be given it
  • 00:13:15
    in any question that involves it Times
  • 00:13:17
    by height in meters technically this
  • 00:13:19
    only gives you a change in gpe as the H
  • 00:13:22
    here should really be changing height
  • 00:13:24
    the higher off the ground on object is
  • 00:13:26
    the more gpe it has or rather the more
  • 00:13:29
    GP it has available to lose if it falls
  • 00:13:32
    to the ground elastic potential energy
  • 00:13:34
    is what we find in say a spring this is
  • 00:13:37
    given by eal half K e^2 that's halftimes
  • 00:13:41
    the spring constant in Newtons per meter
  • 00:13:43
    sometimes called stiffness times
  • 00:13:45
    extension in me squar that's how much
  • 00:13:47
    further the spring has stretched from
  • 00:13:49
    its original length thermal energy or
  • 00:13:51
    change in thermal energy is calculated
  • 00:13:53
    with the shc equation energy equals mass
  • 00:13:56
    * shc * temperature change in De C in
  • 00:14:00
    simple form that's e equal MC delta T
  • 00:14:04
    that Delta or triangle just means change
  • 00:14:06
    in let changeing temperature here shc is
  • 00:14:09
    short for specific heat capacity this
  • 00:14:12
    tells you how much energy is needed to
  • 00:14:13
    raise 1 kilogram of a substance by 1° C
  • 00:14:17
    it's different for every material out
  • 00:14:19
    there remember that an increase in
  • 00:14:21
    thermal energy results in particles
  • 00:14:22
    moving faster so this is essentially a
  • 00:14:25
    way of measuring the kinetic energy
  • 00:14:27
    gained by particles in a substance more
  • 00:14:29
    on this in the particles topic we don't
  • 00:14:31
    really talk about sound or vibrational
  • 00:14:33
    energy as this is just particles moving
  • 00:14:36
    so in reality it's kinetic again
  • 00:14:39
    chemical potential energy say in food or
  • 00:14:42
    fuels there's no equation for that and
  • 00:14:43
    that's more chemistry is remit but you
  • 00:14:45
    might have to mention at some point that
  • 00:14:47
    these two things do have a store of
  • 00:14:49
    chemical potential energy in order for
  • 00:14:52
    anything to happen in a system energy
  • 00:14:54
    must be transferred from one object to
  • 00:14:56
    another or one store to another store in
  • 00:14:59
    a closed system no energy is lost to the
  • 00:15:02
    surroundings no energy in from the
  • 00:15:03
    surroundings either which allows us to
  • 00:15:05
    equate two lots of energy that just
  • 00:15:07
    means saying that two lots of energy are
  • 00:15:09
    the same for example a roller coaster
  • 00:15:12
    car teetering at the top of a ride just
  • 00:15:14
    has GP gravitational potential energy
  • 00:15:16
    basically zero kinetic energy as it
  • 00:15:19
    starts to roll down gpe is turned into K
  • 00:15:23
    okay I should probably say that it gpe
  • 00:15:25
    store is decreasing while it K store is
  • 00:15:27
    increasing instead but all the really
  • 00:15:29
    matters is that at the bottom it's lost
  • 00:15:31
    that gpe using this height here so we
  • 00:15:34
    can say gpe lost equals ke gained gpe
  • 00:15:39
    equals K so if it had this many jewels
  • 00:15:41
    of gpe at the top it must have the same
  • 00:15:44
    number of jewels of K at the bottom we
  • 00:15:47
    can then rearrange the K equation to
  • 00:15:50
    find its speed for example I always
  • 00:15:52
    recommend rearranging equations using
  • 00:15:54
    symbols not words so here I want to make
  • 00:15:56
    V the subject leave it by itself so to
  • 00:15:58
    move something from one side of an
  • 00:16:00
    equation to the other we just do the
  • 00:16:02
    opposite with it to get rid of the half
  • 00:16:03
    we double the other side then to get rid
  • 00:16:06
    of the mass from the right hand side
  • 00:16:07
    well we're multiplying by it on the
  • 00:16:09
    right so we just divide by it on the
  • 00:16:10
    left finally to get rid of the square on
  • 00:16:13
    the V we square root the other side so
  • 00:16:15
    speed V is equal to 2 * the kinetic
  • 00:16:18
    energy divided by the mass or square
  • 00:16:20
    rooted then just pop in your numbers
  • 00:16:22
    punch it into your calculator and boom
  • 00:16:24
    you got your answer you could also
  • 00:16:26
    equate elastic potential energy and
  • 00:16:28
    connect itic energy say if a toy car is
  • 00:16:30
    pulled back on a spring and let go there
  • 00:16:33
    is a shortcut with the whole GP Tok
  • 00:16:35
    scenario by the way if we just equate
  • 00:16:36
    the two equations you'll notice that
  • 00:16:39
    mass m is on both sides so they actually
  • 00:16:41
    cancel out so rearranging this we find
  • 00:16:43
    that V is equal to the square < TK of 2
  • 00:16:46
    g h so really we only need to know the
  • 00:16:48
    height from which something Falls in
  • 00:16:50
    order to know its speed at the bottom if
  • 00:16:52
    you have to rearrange the GP equation
  • 00:16:54
    just remember that the two things you
  • 00:16:55
    have to move from the right hand side
  • 00:16:57
    have to go on the bottom of the left
  • 00:16:58
    hand side multiply together in Brackets
  • 00:17:02
    you could get a situation where for
  • 00:17:03
    example the roller coaster has more GP
  • 00:17:05
    at the top than k at the bottom where's
  • 00:17:08
    the rest of the energy gone you might
  • 00:17:10
    ask well it must have been lost to the
  • 00:17:12
    surroundings so that means it cannot be
  • 00:17:14
    a closed system this could be due to
  • 00:17:17
    work done against air resistance or
  • 00:17:19
    friction work is just another word for
  • 00:17:21
    energy used by the way Wes all Wes
  • 00:17:23
    transfer energy without transferring
  • 00:17:25
    matter oscillations or vibrations are
  • 00:17:27
    passed along instead of the particles
  • 00:17:29
    themselves longitudinal waves are those
  • 00:17:31
    in which the direction of the
  • 00:17:32
    oscillations is parallel to the
  • 00:17:33
    direction of energy transfer that is the
  • 00:17:35
    direction the wave is going examples of
  • 00:17:37
    these are sound waves and seismic p
  • 00:17:39
    waves P stands for primary because
  • 00:17:40
    they're fast in these waves particles
  • 00:17:42
    Bunch up we call those compressions and
  • 00:17:45
    when they're spread out we call those
  • 00:17:46
    rare refractions transverse waves are
  • 00:17:49
    those in which the direction of
  • 00:17:50
    oscillations is perpendicular to the
  • 00:17:52
    direction of energy transfer they wiggle
  • 00:17:54
    side to side or up and down examples are
  • 00:17:57
    waves on the surface of water seismic S
  • 00:18:00
    waves secondary they're slower than p
  • 00:18:01
    waves they produce earthquake after
  • 00:18:03
    shocks and light and also every other em
  • 00:18:07
    electromagnetic wave too we can
  • 00:18:09
    represent any wave including
  • 00:18:10
    longitudinal waves like this we call
  • 00:18:12
    this a waveform displacement is up the
  • 00:18:14
    y- AIS basically just how far the
  • 00:18:16
    particles have oscillated from their
  • 00:18:17
    original position and it can be either
  • 00:18:19
    distance or time on the x-axis the peak
  • 00:18:22
    of a wave is called the amplitude the
  • 00:18:24
    maximum displacement from equilibrium if
  • 00:18:26
    its distance on the x-axis one complete
  • 00:18:29
    wave here gives you the wavelength we
  • 00:18:31
    give this the symbol Lambda for short
  • 00:18:33
    but it's measured in meters if it's time
  • 00:18:35
    on the x-axis instead one complete wave
  • 00:18:38
    gives you the time period capital T for
  • 00:18:40
    short this is the time it takes for one
  • 00:18:42
    complete wave to pass measured in
  • 00:18:44
    seconds frequency on the other hand is
  • 00:18:47
    how many waves pass a point every second
  • 00:18:49
    and the unit is Hertz so frequency and
  • 00:18:52
    time period are the opposite in fact
  • 00:18:54
    they're reciprocals of each other so we
  • 00:18:56
    can say frequency is equal to one over
  • 00:18:59
    time period f = 1/ t you can often be
  • 00:19:02
    asked to find frequency from a waveform
  • 00:19:04
    like this measure the time period Then
  • 00:19:06
    do one divided by that easy the wave
  • 00:19:09
    equation is this V equal F Lambda that's
  • 00:19:11
    wave speed equals frequency time
  • 00:19:14
    wavelength a ripple tank will tell you
  • 00:19:16
    what frequency is made you can measure
  • 00:19:18
    the distance between 10 Peaks then
  • 00:19:19
    divide by 10 to get the wavelength say
  • 00:19:21
    then just use the wave equation to get
  • 00:19:23
    the speed of the wave you could also
  • 00:19:25
    just time how long it takes for a ripple
  • 00:19:26
    in a tray of water to travel the length
  • 00:19:28
    of the trade 10 times then just do total
  • 00:19:30
    distance the by time to get speed
  • 00:19:31
    instead the speed of sound waves can be
  • 00:19:33
    measured by attaching a microphone up to
  • 00:19:35
    oscilloscope for example if you clap
  • 00:19:36
    once next to the microphone the sound
  • 00:19:38
    can Echo off a wall un known distance
  • 00:19:40
    away and it comes back to the microphone
  • 00:19:43
    then you can just use the oscilloscope
  • 00:19:44
    to measure the time it took to travel
  • 00:19:46
    then do total distance divided by time
  • 00:19:48
    again sound waves cause the air drum to
  • 00:19:50
    vibrate which in turn is converted into
  • 00:19:52
    a signal that travels to your brain the
  • 00:19:54
    human ear can hear frequencies between
  • 00:19:55
    20 HZ and 20 khz 20,000 Herz
  • 00:19:59
    any frequency Above This is called
  • 00:20:00
    ultrasound whenever Sound reaches a
  • 00:20:02
    boundary between two different mediums
  • 00:20:04
    materials some of it goes through we say
  • 00:20:07
    it's transmitted while some is reflected
  • 00:20:09
    this is the case when we emit ultrasound
  • 00:20:11
    into a person's body and a computer can
  • 00:20:14
    time how long it takes to return off
  • 00:20:16
    different layers allowing it to build up
  • 00:20:18
    an image of what's inside this allows us
  • 00:20:20
    to scan babies safely we can also time
  • 00:20:23
    sound waves in water to build up a
  • 00:20:25
    picture of what's under a boat or around
  • 00:20:27
    a submarine this is called sonar we've
  • 00:20:30
    mentioned seismic waves already but you
  • 00:20:32
    also need to know that while the
  • 00:20:33
    longitudinal p waves can travel through
  • 00:20:35
    liquids transverse S waves cannot that's
  • 00:20:38
    how we've come to believe that the Earth
  • 00:20:40
    has a molten core there's no Aftershock
  • 00:20:42
    felt when an earthquake happens on the
  • 00:20:44
    other side of the earth which implies
  • 00:20:47
    that there must be a liquid Center when
  • 00:20:49
    waves reflect off a smooth surface we
  • 00:20:52
    say that's specular reflection that just
  • 00:20:55
    means not scattered like a mirror the
  • 00:20:57
    angle of incidence will be equal to the
  • 00:20:59
    angle of reflection all angles are
  • 00:21:01
    measured from the normal which is a line
  • 00:21:03
    we draw perpendicular to the surface if
  • 00:21:05
    light is scattered off a rough surface
  • 00:21:07
    we call this diffuse reflection instead
  • 00:21:10
    em or electromagnetic waves off for
  • 00:21:12
    everybody they're special because they
  • 00:21:14
    don't need a medium to travel through
  • 00:21:15
    they're the only waves that can travel
  • 00:21:17
    through the vacuum of space there are a
  • 00:21:19
    range of wavelengths in the EM spectrum
  • 00:21:21
    which we split up into these sections
  • 00:21:24
    radio waves microwaves
  • 00:21:29
    infrared
  • 00:21:31
    radiation visible light
  • 00:21:35
    ultraviolet
  • 00:21:36
    X
  • 00:21:38
    gam if you haven't heard the original
  • 00:21:41
    version It's a certified Banger Link in
  • 00:21:43
    description EM waves are produced when
  • 00:21:45
    electrons lose energy they lose the
  • 00:21:47
    energy as an EM wave the higher the
  • 00:21:49
    frequency the more energy the wave
  • 00:21:51
    carries and the shorter the wavelength
  • 00:21:53
    The Only Exception are gamma rays which
  • 00:21:55
    are actually emitted by nuclei instead
  • 00:21:57
    that means lots more energy is involved
  • 00:21:59
    that's why they're dangerous they are
  • 00:22:01
    all however absorbed by electrons this
  • 00:22:03
    allows our retina to detect light for
  • 00:22:05
    example phone antennas to receive radio
  • 00:22:08
    signals and your face to absorb infrared
  • 00:22:10
    from the Sun and feel heat UV X-rays and
  • 00:22:13
    gamma rays carry so much energy though
  • 00:22:15
    that they can cause electrons to leave
  • 00:22:17
    their atoms the atoms have been ionized
  • 00:22:19
    that can be dangerous if absorbed by DNA
  • 00:22:22
    and cells as this can cause mutations
  • 00:22:24
    that can lead to cancer while some EM
  • 00:22:26
    waves can be dangerous we use all parts
  • 00:22:28
    of the spectrum for communications
  • 00:22:30
    cooking heating Imaging Medical
  • 00:22:32
    Treatments and more when light waves
  • 00:22:35
    move from one medium to another say from
  • 00:22:37
    Air to Glass they change speed in this
  • 00:22:39
    case the wave slows down and the
  • 00:22:41
    wavelength also decreases instead of
  • 00:22:43
    drawing the wave fronts from above like
  • 00:22:45
    what you see above water we can just
  • 00:22:47
    draw a ray to show the direction that
  • 00:22:49
    the light is moving in that's a lot
  • 00:22:51
    easier a change in medium also results
  • 00:22:53
    in a change in Direction This is called
  • 00:22:55
    refraction that is if it's at an angle
  • 00:22:57
    to the north noral the line we draw
  • 00:22:59
    perpendicular to the surface you can
  • 00:23:01
    think of light always wanting to get
  • 00:23:03
    away from the normal but never write
  • 00:23:05
    that in the exam if light slows down it
  • 00:23:07
    moves closer to the normal so that means
  • 00:23:09
    that the angle of refraction is smaller
  • 00:23:12
    than the angle of incidence that's the
  • 00:23:13
    angle that it hits the surface at now
  • 00:23:16
    all of these angles are measured from
  • 00:23:18
    the normal that means you must have your
  • 00:23:20
    protractor with the zero on the normal
  • 00:23:23
    never have it flat on the surface it's
  • 00:23:26
    always perpendicular to the surface
  • 00:23:28
    let's say the light rate is coming out
  • 00:23:30
    of the glass block and into air now if
  • 00:23:32
    we keep increasing this angle of
  • 00:23:34
    incidence eventually we'll end up with
  • 00:23:36
    an angle of refraction of 90° that light
  • 00:23:38
    Ray will be going along that boundary
  • 00:23:41
    along the surface the angle of incidence
  • 00:23:43
    is now equal to what we call the
  • 00:23:45
    critical angle and that's going to be
  • 00:23:46
    different for every medium if we make
  • 00:23:48
    the angle of incidence even bigger than
  • 00:23:50
    the critical angle that means that no
  • 00:23:52
    light is going to be refracted out of
  • 00:23:53
    the block instead all light is reflected
  • 00:23:56
    back inside by the way we all always get
  • 00:23:58
    some reflection but now we have total
  • 00:24:01
    internal reflection this incidentally is
  • 00:24:04
    how optic fibers or fiber optics work
  • 00:24:06
    the basic premise is that we have a very
  • 00:24:08
    thin but still solid glass fiber we send
  • 00:24:12
    light down it and because when the Light
  • 00:24:14
    reaches the surface the angle of
  • 00:24:16
    incidence is so large the light isn't
  • 00:24:17
    refracted out it's TI it's totally
  • 00:24:20
    internally reflected and it bounces
  • 00:24:22
    along the optic fiber no mirrors needed
  • 00:24:25
    this allows us to send a huge amount of
  • 00:24:27
    information very quickly
  • 00:24:29
    lenses oh boy here we go okay lenses are
  • 00:24:32
    curved blocks of glass also you have
  • 00:24:34
    them in your eyes they use refraction to
  • 00:24:36
    make rays of light converge meet or
  • 00:24:39
    diverge spread out a convex lens can
  • 00:24:42
    make Rays converge this is the symbol we
  • 00:24:44
    use to represent it if Rays enter
  • 00:24:47
    parallel to what we call the principal
  • 00:24:48
    axis for example the light from an
  • 00:24:51
    object very far away the lens will make
  • 00:24:53
    the Rays converge at this point here
  • 00:24:55
    this is called the principal Focus the
  • 00:24:57
    distance from the center of the lens is
  • 00:24:59
    called the focal length this doesn't
  • 00:25:00
    change for a lens and we can draw it on
  • 00:25:02
    both sides and you'll see why in a bit
  • 00:25:04
    however light doesn't usually come from
  • 00:25:06
    objects infinitely far away but from
  • 00:25:08
    objects a little bit nearer the object
  • 00:25:10
    could be anything but we often represent
  • 00:25:12
    it with just an arrow convex lens can
  • 00:25:14
    then project an image using the light
  • 00:25:16
    that comes from the object but we only
  • 00:25:18
    consider the light coming from the top
  • 00:25:19
    of the object and we can do that by
  • 00:25:21
    drawing two rays one always goes
  • 00:25:23
    straight through the center of the lens
  • 00:25:24
    and one goes parallel into the lens then
  • 00:25:27
    through the principal Focus where these
  • 00:25:29
    two rays meet is where the image is
  • 00:25:31
    formed that's where you want your
  • 00:25:33
    projector screen or retina or camera
  • 00:25:35
    sensor to be in order to get a clear
  • 00:25:37
    image formed you'll also notice that the
  • 00:25:39
    image is smaller than the object so we
  • 00:25:41
    say it's diminished it's also upside
  • 00:25:43
    down so we say it's inverted things get
  • 00:25:46
    a bit trickier when the object is very
  • 00:25:47
    close to the lens now the Rays don't
  • 00:25:49
    meet the image can't be projected
  • 00:25:52
    however if we extrapolate the two rays
  • 00:25:54
    back behind the lens they do meet we can
  • 00:25:57
    draw the image here here and we can say
  • 00:25:59
    that it's magnified it's upright but
  • 00:26:01
    it's virtual that means that it can't be
  • 00:26:04
    projected it's no longer a real image
  • 00:26:07
    like we had before this would be what a
  • 00:26:09
    magnifying glass does for example your
  • 00:26:11
    eye can deal with this diverging light
  • 00:26:13
    accordingly to make it focus on your
  • 00:26:15
    retina but that means that you see this
  • 00:26:17
    magnified virtual image so things appear
  • 00:26:19
    bigger concave lenses always diverge
  • 00:26:22
    like Rays so they always produce a
  • 00:26:24
    virtual image with these our line
  • 00:26:26
    parallel in goes back through the other
  • 00:26:29
    principal Focus behind the lens where it
  • 00:26:31
    meets the other Ray is where the virtual
  • 00:26:33
    image is this image is also diminished
  • 00:26:36
    and upright as you can see the
  • 00:26:38
    magnification of a lens is just the
  • 00:26:39
    ratio of image height to object height a
  • 00:26:42
    magnification greater than one means the
  • 00:26:44
    image is bigger than the object less
  • 00:26:47
    than one it's diminished it's smaller
  • 00:26:49
    than the object what we perceive as
  • 00:26:51
    color is a result of different
  • 00:26:52
    wavelengths of light being emitted by a
  • 00:26:54
    source or reflected by an object that
  • 00:26:57
    are then absorbed by the the cells in
  • 00:26:58
    our retina most objects will absorb some
  • 00:27:00
    wavelengths of light while reflect
  • 00:27:02
    others for example chlorophyll in Plants
  • 00:27:05
    absorbs longer red wavelengths of Light
  • 00:27:07
    which is why leaves appear green it
  • 00:27:10
    reflects those shorter wavelengths this
  • 00:27:12
    ball looks blue in sunlight because it
  • 00:27:14
    reflects the blue wavelengths of light
  • 00:27:16
    shine just red light on it though and it
  • 00:27:18
    will appear black as that red light will
  • 00:27:21
    be absorbed no light will be reflected
  • 00:27:23
    the term radiation means any particle or
  • 00:27:26
    wave that's emitted by something the
  • 00:27:27
    electrom magnetic spectrum is all
  • 00:27:29
    radiation but they're all emitted by
  • 00:27:31
    electrons all apart from gamma radiation
  • 00:27:33
    that is gamma radiation is actually
  • 00:27:35
    emitted by the nucleus of an atom if it
  • 00:27:37
    has excess energy it's getting rid of
  • 00:27:39
    gamma rays are high energy em WS they
  • 00:27:42
    can be dangerous as they can ionize
  • 00:27:44
    atoms if absorbed by them knocking
  • 00:27:46
    electrons off this can cause damage to
  • 00:27:48
    the cells in your body and also cause
  • 00:27:50
    cancer but there are two other types of
  • 00:27:52
    radiation nuclei can emit too but these
  • 00:27:55
    are actual particles and they're emitted
  • 00:27:57
    when nuclei Decay change isotopes with
  • 00:28:00
    more neutrons are generally more
  • 00:28:02
    unstable and likely to Decay heavier
  • 00:28:05
    nuclei like amorium 241 Decay by what we
  • 00:28:08
    call alpha decay to become more stable
  • 00:28:11
    the nucleus will emit a bundle of two
  • 00:28:13
    protons and two neutrons what we can
  • 00:28:16
    just call an alpha particle this is
  • 00:28:18
    Alpha radiation this is what the nuclear
  • 00:28:20
    decay equation would look like for this
  • 00:28:22
    to show that the nucleus has decayed
  • 00:28:24
    into two parts the alpha particle which
  • 00:28:26
    must have an atomic number of two and
  • 00:28:28
    mass of four and the daughter nucleus
  • 00:28:30
    that's just the nucleus left over which
  • 00:28:32
    of course is no longer going to be
  • 00:28:34
    amorium as it's lost protons to go from
  • 00:28:36
    an atomic number of 95 to 93 turns out
  • 00:28:39
    that's neptunium but you'll never have
  • 00:28:41
    to remember these you just need to worry
  • 00:28:43
    about the numbers it's just maths 95
  • 00:28:46
    goes to 93 + 2 and the math is similar
  • 00:28:49
    241 goes to 237 and4 there is actually a
  • 00:28:53
    nucleus that has the numbers two and
  • 00:28:54
    four it's a helium nucleus you should
  • 00:28:57
    write he instead of an alpha symbol in a
  • 00:29:00
    decay equation I much prefer saying
  • 00:29:02
    Alpha but you should get the mark either
  • 00:29:04
    way lighter Isotopes lighter nuclei like
  • 00:29:06
    carbon 14 Decay by Beta Decay or beta
  • 00:29:09
    Decay instead what happens is that a
  • 00:29:11
    neutron in the nucleus turns into a
  • 00:29:13
    proton and an electron but the fast
  • 00:29:15
    moving electron that's ejected by the
  • 00:29:17
    nucleus escapes and we now call this
  • 00:29:19
    beta radiation the mass of an electron
  • 00:29:21
    is basically zero so we put that on top
  • 00:29:24
    it has the opposite charge to a proton
  • 00:29:25
    so we say it has an atomic number of
  • 00:29:27
    minus one now be careful here 6 goes to
  • 00:29:30
    what plus minus one no it's not five
  • 00:29:34
    it's seven 6 is equal to 7 + - one like
  • 00:29:37
    we said a neutron has turned into a
  • 00:29:39
    proton so the nucleus has gained a
  • 00:29:41
    proton it's gone from 6 to 7 the mass
  • 00:29:44
    however is unchanged so it's still 14
  • 00:29:47
    alpha particles are massive and have a
  • 00:29:49
    relatively large charge so as they
  • 00:29:51
    travel they knock loads of electrons off
  • 00:29:53
    loads of atoms in their way we say they
  • 00:29:55
    have a high ionizing ability or High
  • 00:29:58
    ionizing power but as a result they're
  • 00:30:00
    stopped easily they're absorbed by a few
  • 00:30:02
    centimeters of air or just a piece of
  • 00:30:04
    paper if you have a Geer Muller tube a
  • 00:30:07
    GM tube touching a source of alpha
  • 00:30:09
    radiation like amarium it will detect
  • 00:30:12
    the alpha radiation emitted move it a
  • 00:30:14
    bit further away or stick a piece of
  • 00:30:15
    paper between and the radiation counts
  • 00:30:17
    per second will fall to zero or near
  • 00:30:20
    zero anyway I say near zero because
  • 00:30:22
    there are background sources of
  • 00:30:24
    radiation from the world around us
  • 00:30:25
    raidon gas comes out of concrete and
  • 00:30:27
    rocks that's slightly radioactive cosmic
  • 00:30:30
    rays from space are also background
  • 00:30:31
    radiation man-made radiation like that
  • 00:30:34
    from nuclear weapons contribute to it
  • 00:30:36
    too so if you want an accurate radiation
  • 00:30:38
    count over a minute from an alpha Source
  • 00:30:40
    say you should do a background count
  • 00:30:42
    first then take that number away from
  • 00:30:44
    the count with the source that will give
  • 00:30:46
    you a corrected count Alpha radiation
  • 00:30:48
    can be useful however it's used in smoke
  • 00:30:50
    detectors beta radiation is not as
  • 00:30:52
    ionizing as Alpha but it has higher
  • 00:30:54
    penetrating power it's fairly good at
  • 00:30:56
    both it can room or air and a piece of
  • 00:30:59
    paper easily but it's absorbed by a few
  • 00:31:01
    millimet of aluminium it can be used to
  • 00:31:04
    detect thickness of thin materials like
  • 00:31:06
    paper when made in a mill gamma
  • 00:31:08
    radiation has low ionizing ability so
  • 00:31:11
    why is it so dangerous well it's because
  • 00:31:13
    it can actually get to you technically
  • 00:31:15
    there's nothing that can completely stop
  • 00:31:17
    gamma radiation but lead and concrete
  • 00:31:19
    can reduce the intensity of it by
  • 00:31:21
    absorbing some of it gamma has many uses
  • 00:31:23
    actually it can be used for radiotherapy
  • 00:31:25
    or gamma knife surgery to kill cancer
  • 00:31:27
    tumors in your brain for example and it
  • 00:31:29
    can be used to sterilize medical
  • 00:31:31
    equipment as it kills any microbes on
  • 00:31:33
    the scalpel Etc sometimes nuclei can
  • 00:31:35
    emit neutrons as radiation under special
  • 00:31:38
    circumstances you'll see this in fision
  • 00:31:40
    in a minute but it's worth knowing that
  • 00:31:42
    while alpha beta and gamma can ionize
  • 00:31:44
    atoms they can't make other atoms
  • 00:31:45
    radioactive themselves they can't cause
  • 00:31:47
    other nuclei to become unstable and
  • 00:31:49
    Decay neutrons however can that's why
  • 00:31:52
    you must dispose of the concrete around
  • 00:31:54
    the nuclear reactor carefully as it will
  • 00:31:56
    have been bombarded with neutral causing
  • 00:31:58
    its atoms to become unstable
  • 00:32:00
    radioactivity is the rate of decay of a
  • 00:32:02
    source of Alpha Beta or gamma now you
  • 00:32:05
    know not really Decay with gamma but the
  • 00:32:06
    same idea this rate can be measured with
  • 00:32:09
    a GM tube like we said and we can
  • 00:32:11
    calculate it by doing radiation count
  • 00:32:13
    divided by time in seconds this gives
  • 00:32:15
    you the radio activity sometimes just
  • 00:32:17
    called activity in counts per second
  • 00:32:20
    which is also called Beckel BQ for short
  • 00:32:23
    over time the number of unstable nuclei
  • 00:32:25
    in a sample or Source decreases as
  • 00:32:27
    they're decaying into something else so
  • 00:32:29
    that means the activity decreases too
  • 00:32:32
    halflife is what we call the time it
  • 00:32:33
    takes for both of these to half actually
  • 00:32:36
    it also goes for Mass too the half life
  • 00:32:38
    of a radioactive isotope could be days
  • 00:32:40
    months even millions of years long if we
  • 00:32:42
    draw a graph to show how activity
  • 00:32:44
    changes over time it might look
  • 00:32:46
    something like this how do we find the
  • 00:32:47
    halflife well we take the initial number
  • 00:32:50
    have it then draw a line to the curve to
  • 00:32:52
    see how long that took what's
  • 00:32:54
    interesting is that if we do the same
  • 00:32:56
    again it will take the same same amount
  • 00:32:58
    of time to half it doesn't matter how
  • 00:32:59
    much of the isotope you have or when you
  • 00:33:01
    start timing it will always take the
  • 00:33:03
    same amount of time to half you could be
  • 00:33:05
    asked to calculate halflife let's say
  • 00:33:07
    that we have a sample that started at 96
  • 00:33:10
    beel activity and it fell to 12 beel
  • 00:33:13
    after one year 12 months the question
  • 00:33:15
    you always have to ask is how many half
  • 00:33:17
    lives you don't do 96 ided by 12 but
  • 00:33:20
    instead count how many times you have to
  • 00:33:22
    half it to get to the second number one
  • 00:33:24
    half life 48 Beckel two half lives 24
  • 00:33:28
    three Half Lives 12 it took three Half
  • 00:33:31
    Lives to decrease to 12 becko so if 12
  • 00:33:34
    months is three half lives that must
  • 00:33:36
    mean that one half life is a third of
  • 00:33:38
    that 12 divided by three the half life
  • 00:33:41
    is 4 months just some triple stuff to
  • 00:33:43
    finish off if you take a nucleus like
  • 00:33:45
    uranium 235 and fire a neutron at it
  • 00:33:49
    that Neutron will be absorbed and will
  • 00:33:50
    make the nucleus more unstable instead
  • 00:33:52
    of decaying by alpha or beta it actually
  • 00:33:55
    splits in half producing two similar do
  • 00:33:57
    to nuclei this is nuclear fision what's
  • 00:34:00
    weird though is that the total mass of
  • 00:34:02
    the products of this fion is less than
  • 00:34:04
    what we had to begin with how's that
  • 00:34:06
    possible well it turns out that mass can
  • 00:34:08
    turn into energy in these situations yes
  • 00:34:11
    we say that energy can't be created or
  • 00:34:13
    destroyed but at this level we say that
  • 00:34:15
    the reactants have mass energy to get
  • 00:34:17
    around that the energy produced is
  • 00:34:19
    thermal or more ularly kinetic as we
  • 00:34:21
    talked about earlier the clever thing is
  • 00:34:23
    is that this fion also releases up to
  • 00:34:25
    three more neutrons that can go off and
  • 00:34:28
    cause more fision in other nuclei
  • 00:34:30
    themselves and so on and more energy is
  • 00:34:32
    released we now have a chain reaction
  • 00:34:35
    left unchecked this can go out of
  • 00:34:37
    control that's what an atomic or nuclear
  • 00:34:39
    bomb is however if you control this
  • 00:34:41
    chain reaction in a nuclear reactor you
  • 00:34:43
    can produce a consistently safe and huge
  • 00:34:46
    amount of energy that can be used to
  • 00:34:47
    then produce electricity by heating
  • 00:34:49
    steam to turn a turbine connected to a
  • 00:34:51
    generator Etc Fusion however is what
  • 00:34:53
    happens in the Sun to produce energy
  • 00:34:55
    from Mass two light nuclei like hydrogen
  • 00:34:58
    fused together into one heavier one
  • 00:35:01
    helium in this case and energy is
  • 00:35:03
    released but only if they have a lot of
  • 00:35:05
    kinetic energy to begin with but hang on
  • 00:35:07
    how can both fion and fusion result in
  • 00:35:09
    energy being released well it's all to
  • 00:35:11
    do with what nuclei you have to begin
  • 00:35:13
    with if you want to know more about this
  • 00:35:15
    do a level physics or watch my binding
  • 00:35:17
    energy video scientists have been trying
  • 00:35:19
    to make fusion reactors for decades but
  • 00:35:21
    they haven't managed to make one where
  • 00:35:23
    they're able to harness enough energy
  • 00:35:24
    from the radiation released from the
  • 00:35:26
    process for it to be viable our solar
  • 00:35:29
    system consists of the sun with the
  • 00:35:31
    eight planets orbiting it with an
  • 00:35:33
    asteroid belt as well between Mars and
  • 00:35:35
    Jupiter and other dwarf planets too poor
  • 00:35:38
    old Pluto our moon and other planets
  • 00:35:40
    moons are natural satellites our solar
  • 00:35:43
    system is one of many found in our
  • 00:35:45
    galaxy which we call the Milky Way it's
  • 00:35:47
    believed that stars are the result of
  • 00:35:49
    dust and gas particles in clouds we call
  • 00:35:52
    such a cloud a nebula being attracted to
  • 00:35:54
    each other due to gravity the cloud
  • 00:35:56
    becomes hotter run more dense until
  • 00:35:58
    Fusion starts to occur a star will
  • 00:36:01
    remain stable so long as the outward
  • 00:36:03
    pressure from Fusion and the force of
  • 00:36:05
    gravity pulling inward remain balanced
  • 00:36:08
    we say it's in the main sequence stage
  • 00:36:10
    of its life when a star dies the outward
  • 00:36:12
    pressure increases which causes it to
  • 00:36:14
    expand turning it into a red giant if
  • 00:36:17
    it's a star a similar size to our sun or
  • 00:36:19
    a super red giant for stars much bigger
  • 00:36:21
    than our son a red giant will then
  • 00:36:23
    collapse once all the fuel for Fusion
  • 00:36:25
    has run out leaving a white dwarf and
  • 00:36:27
    then a black dwarf once it's cooled a
  • 00:36:30
    super red giant explodes we say it's
  • 00:36:32
    gone Supernova leaving a very dense
  • 00:36:34
    neutron star at the center or an even
  • 00:36:37
    more dense body that causes a black hole
  • 00:36:39
    there the outer layers of the Supernova
  • 00:36:41
    move away forming new nebula from which
  • 00:36:44
    new stars could be made nuclei fused
  • 00:36:47
    together to make heavier elements some
  • 00:36:48
    of these could only be made as a result
  • 00:36:50
    of the huge amount of energy released
  • 00:36:52
    from a
  • 00:36:53
    supernova our moon is a natural
  • 00:36:55
    satellite while Elon makes artificial
  • 00:36:58
    satellites in both cases they orbit the
  • 00:37:00
    earth some satellites orbit in a circle
  • 00:37:03
    around the earth Like geostationary
  • 00:37:05
    Satellites these sit above the same spot
  • 00:37:07
    above the equator and they're used for
  • 00:37:09
    GPS and communication they move at a
  • 00:37:12
    constant speed yet their direction is
  • 00:37:14
    constantly changing so technically their
  • 00:37:16
    velocity is constantly changing which
  • 00:37:18
    means that they're accelerating towards
  • 00:37:20
    the Earth they just don't get any closer
  • 00:37:23
    as they go too fast any force that
  • 00:37:25
    results in circular motion is called the
  • 00:37:27
    Cent copal force and that always acts
  • 00:37:29
    towards the center of its orbit we can
  • 00:37:31
    draw the velocity at any point as a
  • 00:37:34
    tangent so if the Earth suddenly
  • 00:37:36
    disappeared that's where this satellite
  • 00:37:38
    would fly off that means that copal
  • 00:37:40
    force and velocity are always at right
  • 00:37:42
    angles to each other they're
  • 00:37:43
    perpendicular other satellites travel in
  • 00:37:46
    elliptical orbits and they're used for
  • 00:37:47
    reconnaissance and weather for example
  • 00:37:50
    the closer they get to the Earth the
  • 00:37:51
    faster they move and vice versa we have
  • 00:37:54
    a good idea of what wavelengths of light
  • 00:37:56
    are emitted from Stars
  • 00:37:58
    however when we look at distant stars
  • 00:37:59
    and galaxies these wavelengths appear
  • 00:38:01
    longer they're shifted towards the red
  • 00:38:03
    end of the spectrum the light has been
  • 00:38:06
    red shifted much like when the pitch of
  • 00:38:08
    an ambulance siren drops when it's
  • 00:38:10
    moving away from you
  • 00:38:13
    like this shows the galaxies must be
  • 00:38:15
    moving away from us and this is the case
  • 00:38:18
    in every direction we look not only that
  • 00:38:20
    the light from more distant galaxies is
  • 00:38:22
    even more red shifted suggesting they're
  • 00:38:25
    moving faster away from us rece eding
  • 00:38:27
    faster we say at a faster rate this
  • 00:38:30
    implies that if we go back in time all
  • 00:38:33
    of these galaxies appear to have
  • 00:38:35
    originated from the same point in space
  • 00:38:38
    this is therefore used as evidence for
  • 00:38:39
    the Big Bang Theory and that the
  • 00:38:41
    observable universe is still expanding
  • 00:38:44
    the other piece of evidence for it is
  • 00:38:46
    cmbr Cosmic microwave background
  • 00:38:48
    radiation outer space might look dark
  • 00:38:51
    but we can detect microwave radiation
  • 00:38:53
    being emitted from very far away from
  • 00:38:55
    all directions this could be committed
  • 00:38:57
    as a result of matter still cooling down
  • 00:39:00
    so it seems we're looking at the edge of
  • 00:39:02
    the Big Bang which is essentially still
  • 00:39:05
    going and that's it hopefully this has
  • 00:39:07
    been useful leave a like if it has and
  • 00:39:09
    leave any comments or questions you have
  • 00:39:11
    below and hey come back here after the
  • 00:39:12
    exam to let us all know how you got on
  • 00:39:14
    we'd love to know click on a card to go
  • 00:39:16
    to the playlist for all six papers and
  • 00:39:18
    I'll see you next time best of luck
Tag
  • Physics
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