Hewitt-Drew-it! PHYSICS 89. Electric Fields

00:09:38
https://www.youtube.com/watch?v=9nlflkR8tvs

Resumen

TLDRThe video elaborates on the concept of force fields in both gravitational and electric contexts, illustrating how these forces operate over a distance between two bodies. It explains that a force field represents the region where a force can be felt by nearby objects, using gravitational and electric examples. The gravitational field around a planet is depicted with vector lines to show the direction and strength, which diminishes with distance (inverse square law). Similarly, an electric field around a charge is described, highlighting that the force on a charge is equal to the electric field strength times the charge. The video further details the vector nature of fields, clarifying how direction and magnitude play roles in field-pattern creation. It shows how sum of field vectors can lead to curly lines signifying field direction. In practical terms, the operation of a Van de Graaff generator is explained, illustrating how charge accumulates without increasing the inner field, which remains zero. The video concludes with an exploration of concepts like electric induction, field cancellation, and potential applications, prompting viewers to think critically about these forces.

Para llevar

  • 🔋 Electric and gravitational forces operate over distances without contact.
  • 📏 Force fields describe these non-contact forces from a conceptual standpoint.
  • ⚡ Electric fields for charged particles are vector quantities like gravitational fields.
  • ➡️ The magnitude of the electric field is the force experienced per unit charge.
  • 🌀 Field lines for electric forces can be straight for single charges or curved between pairs.
  • 🔍 Inside charged conductors, the electric field cancels and is zero.
  • 🌩️ Van de Graaff generators demonstrate field concepts by creating high voltages safely.
  • 🔅 Hair standing on end near Van de Graaff is due to repulsive electric forces between same-charged strands.
  • ⚖️ Voltage should be understood as energy per charge unit, differentiating from direct current cause of shock.
  • 🔁 The cancellation of fields between charges emphasizes symmetrical force interactions.

Cronología

  • 00:00:00 - 00:09:38

    The video continues to explore electric field patterns, showing that a composite of force vectors creates a curved field from positive to negative charges. It illustrates this with photographs of electric fields in different setups, such as terminals in oil and plates in a capacitor. The video highlights that no field results inside a charged conductor, covered in detail later in textbooks. Using a Vandegraff generator as an example, it illustrates how charges build up outside but remain zero inside, enabling continuous charge accumulation until electric discharge occurs. It discusses why people touching the charged generator aren't shocked despite high voltages due to energy per charge being minimal. Finally, it poses a conceptual question about the nature of charges when their electric fields cancel out midway between them, prompting viewers to consider if the charges are like or unlike.

Mapa mental

Mind Map

Preguntas frecuentes

  • What are force fields in physics?

    Force fields in physics refer to the area over which a force is exerted, such as gravitational or electric fields, without direct contact between objects.

  • How do gravitational and electric fields compare?

    Both gravitational and electric fields operate by exerting forces over a distance. They are vector quantities describing forces between masses or charges.

  • What is the unit of a gravitational or electric field?

    The unit for both gravitational and electric fields is Newton per kilogram (N/kg) for gravitational fields and Newton per Coulomb (N/C) for electric fields.

  • How is the force on a charge in an electric field calculated?

    The force is calculated by multiplying the charge by the electric field strength (F = qE).

  • What happens inside a charged conductor regarding the electric field?

    Inside a charged conductor, the electric field strength is zero because all field lines cancel each other out.

  • What is special about the field between a pair of positive charges?

    The field between two positive charges results in zero directly at the midpoint between them due to equal repelling forces.

  • Why does hair stand on end when touching a Van de Graaff generator?

    Hair strands stand on end because they become electrically charged and repel each other due to similar charges.

  • Why is touching a charged Van de Graaff generator generally safe?

    It is safe because the charges involved carry very low energy, despite the high voltage, due to small charge amounts.

  • What is required to understand about electric fields when considering voltage?

    When considering voltage, it's important to understand it as a ratio of energy per charge (Joules/Coulomb).

  • What determines whether combined electric fields cancel to zero between charged particles?

    The signs (like or unlike) of the charged particles determine this; typically, opposite charges can mutually cancel out their fields at a midpoint.

Ver más resúmenes de vídeos

Obtén acceso instantáneo a resúmenes gratuitos de vídeos de YouTube gracias a la IA.
Subtítulos
en
Desplazamiento automático:
  • 00:00:01
    [Music]
  • 00:00:04
    electric forces like gravitational
  • 00:00:06
    forces most often act between bodies
  • 00:00:09
    that are not in contact these forces act
  • 00:00:11
    over a distance no contact necessary a
  • 00:00:15
    conceptual way to describe forces acting
  • 00:00:17
    at a distance involves the concept of a
  • 00:00:19
    force field consider this planet in
  • 00:00:22
    space these Orange Lines represent
  • 00:00:25
    gravitational field lines about the
  • 00:00:27
    planet any mass in this gravitational
  • 00:00:30
    force field experiences a
  • 00:00:32
    force is the force acting on a satellite
  • 00:00:34
    of mass m in the
  • 00:00:36
    field in previous lessons we've
  • 00:00:38
    described the gravitational force in
  • 00:00:40
    such a satellite with Newton's law of
  • 00:00:43
    gravity an equivalent way is multiplying
  • 00:00:46
    the mass of the Satellite by the
  • 00:00:47
    gravitational field of the planet where
  • 00:00:50
    the satellite is
  • 00:00:52
    located then the force F on the
  • 00:00:54
    satellite is its mass times the
  • 00:00:57
    gravitational field G
  • 00:01:00
    this is bold-faced g to distinguish it
  • 00:01:03
    from the italic G we often use for
  • 00:01:05
    acceleration due to gravity near Earth's
  • 00:01:07
    surface both G's have units Newtons per
  • 00:01:11
    kilogram the field is stronger up close
  • 00:01:14
    and weakens with the inverse square of
  • 00:01:16
    distance the field plays an intermediate
  • 00:01:19
    role between objects likewise in
  • 00:01:22
    electricity here's a proton surrounded
  • 00:01:24
    by its electric
  • 00:01:26
    field the electric field is denoted by
  • 00:01:28
    the symbol e
  • 00:01:31
    and here's an electron circling the
  • 00:01:33
    proton and what of the force on the
  • 00:01:35
    electron much akin to gravity the force
  • 00:01:38
    equals its electric charge multiplied by
  • 00:01:40
    the proton's electric field
  • 00:01:43
    QE the magnitude of the electric field
  • 00:01:46
    is simply the force per unit charge if a
  • 00:01:49
    charge Q experiences a force F at some
  • 00:01:51
    point in space then the electric field
  • 00:01:53
    at that point is f / Q when the force is
  • 00:01:58
    expressed in Newtons and the charge kums
  • 00:02:00
    denoted by the capital letter C the
  • 00:02:03
    electric field has the unit Newton per
  • 00:02:06
    Kum n / C both the fields for gravity
  • 00:02:10
    and electricity are vector quantities
  • 00:02:12
    having direction as well as magnitude
  • 00:02:14
    and can be represented by Vector
  • 00:02:17
    arrows the direction of Earth's
  • 00:02:19
    gravitational field is toward Earth
  • 00:02:21
    inward the direction of force on a mass
  • 00:02:23
    in the field the direction of the
  • 00:02:26
    electric field about the proton is the
  • 00:02:28
    direction of force on a POS positive
  • 00:02:30
    charge in the field outward since our
  • 00:02:33
    charge is negative here that of an
  • 00:02:35
    electron the force on it is opposite to
  • 00:02:38
    the direction of the
  • 00:02:40
    field here's a positive charge with a
  • 00:02:43
    few of its field lines they Point
  • 00:02:45
    radially outward but what of the field
  • 00:02:48
    lines about a pair of equal and opposite
  • 00:02:51
    charges we get this pattern a pattern of
  • 00:02:54
    curved lines it's interesting to realize
  • 00:02:57
    that the curved pattern is the composite
  • 00:03:00
    of pairs of straight lines outward from
  • 00:03:02
    the positive charge and inward toward
  • 00:03:04
    the negative charge for example consider
  • 00:03:08
    the field at this point where I place a
  • 00:03:10
    Green
  • 00:03:11
    Dot a positive test charge here would
  • 00:03:14
    feel a repelling force from the positive
  • 00:03:16
    charge and an attractive Force toward
  • 00:03:18
    the negative
  • 00:03:20
    charge at this point here's the force
  • 00:03:22
    Vector due to the positive
  • 00:03:25
    charge here's the force Vector showing
  • 00:03:27
    attraction to the negative charge
  • 00:03:30
    we see it smaller in accord with the
  • 00:03:32
    inverse Square
  • 00:03:34
    law we draw a parallelogram for these
  • 00:03:37
    two vectors and this gives us the
  • 00:03:39
    resultant Force at this location right
  • 00:03:42
    here where the Green Dot
  • 00:03:45
    is not its direction coincides with the
  • 00:03:48
    direction of the composite field at this
  • 00:03:51
    point let's do the same for this point a
  • 00:03:54
    force in a direction away from the
  • 00:03:56
    positive
  • 00:03:57
    charge and a force of attraction toward
  • 00:04:00
    the negative
  • 00:04:02
    charge and using the parallelogram rule
  • 00:04:06
    we get the resultant vector and again it
  • 00:04:09
    aligns with a composite field at that
  • 00:04:12
    point we do the same for this
  • 00:04:15
    point and the
  • 00:04:18
    parallelogram and see
  • 00:04:20
    that alignment with the field at this
  • 00:04:23
    point and for this point same
  • 00:04:28
    story I I could repeat this process with
  • 00:04:31
    all the points in the electric field and
  • 00:04:33
    you know what I'd get the curved pattern
  • 00:04:36
    you see a composite of resultant Force
  • 00:04:39
    vectors over an infinite number of
  • 00:04:42
    points a curved field that begins at the
  • 00:04:45
    positive charge and ends at the negative
  • 00:04:47
    charge is this yum or
  • 00:04:50
    what let's take a look at some
  • 00:04:52
    photographs of electric field
  • 00:04:56
    patterns here's a photograph of such
  • 00:04:59
    field Lin about a positive and negative
  • 00:05:01
    terminal in a bath of oil the field is
  • 00:05:05
    shown by the orientation of bits of
  • 00:05:07
    thread suspended in the oil and not
  • 00:05:10
    surprisingly the field formed by the
  • 00:05:12
    pair of equal and opposite charges is
  • 00:05:14
    like the field I just
  • 00:05:16
    sketched we can use the same Vector
  • 00:05:19
    technique to show the field between a
  • 00:05:21
    pair of positive terminals shown here
  • 00:05:24
    what's the resultant field halfway
  • 00:05:26
    between the equal charges did you say
  • 00:05:29
    zero if so
  • 00:05:32
    yum here's a photo of field lines
  • 00:05:34
    between oppositely charged plates called
  • 00:05:37
    a capacitor notice the field is uniform
  • 00:05:40
    between the plates except near the edges
  • 00:05:43
    why the field isn't uniform between the
  • 00:05:45
    edges is something we won't get into in
  • 00:05:47
    this
  • 00:05:49
    lesson but here's detail for a
  • 00:05:52
    capacitor both plates have equal and
  • 00:05:54
    opposite
  • 00:05:56
    charges and chyo physics instructor Mona
  • 00:05:59
    Asser models a demonstration
  • 00:06:03
    capacitor back to our field patterns
  • 00:06:06
    very interesting is the field pattern
  • 00:06:08
    for a plate and cylinder that have
  • 00:06:10
    opposite
  • 00:06:12
    charges notice the absence of a field
  • 00:06:15
    inside the charged cylinder all field
  • 00:06:18
    lines cancel out why this is true is
  • 00:06:22
    even more interesting covered of course
  • 00:06:24
    in your textbook for now we just want to
  • 00:06:27
    say that inside any charged body the
  • 00:06:29
    field strength is zero all field vectors
  • 00:06:33
    cancel again covered in conceptual
  • 00:06:37
    physics the fact that no field results
  • 00:06:39
    inside a Charged conductor is nicely
  • 00:06:42
    employed in the vandag graph
  • 00:06:45
    generator let's look at the operation of
  • 00:06:47
    a vandag graph
  • 00:06:50
    generator we see that a voltage source
  • 00:06:53
    leaks charge off metal points in this
  • 00:06:55
    case
  • 00:06:56
    electrons an insulating belt carries the
  • 00:06:59
    electron R up inside an electrically
  • 00:07:01
    insulated tube that supports the hollow
  • 00:07:03
    doome
  • 00:07:05
    above electrons leak off onto the metal
  • 00:07:08
    Point collectors at the top of their
  • 00:07:10
    path and repel one another and gather on
  • 00:07:12
    the outside of the metal
  • 00:07:15
    sphere no matter how much net charge
  • 00:07:18
    accumulates on the outside of the Dome
  • 00:07:20
    field strength inside is zero that means
  • 00:07:24
    charge can be added if introduced inside
  • 00:07:26
    the Dome without repelling away whereas
  • 00:07:29
    any charge that approaches the outside
  • 00:07:31
    of the charge Dome is repelled away
  • 00:07:34
    inside not the case the result is that
  • 00:07:38
    charge can keep building up of the
  • 00:07:39
    dome's outer surface until the buildup
  • 00:07:42
    voltages produce Electric discharge
  • 00:07:44
    through the air then we have localized
  • 00:07:47
    lightning
  • 00:07:48
    bolts here we see lri Patterson touching
  • 00:07:51
    a Charged vandag graph
  • 00:07:53
    generator note how her hair stands out
  • 00:07:56
    that's because it becomes electrically
  • 00:07:58
    charged and strand of her hair are light
  • 00:08:00
    enough to show the electric repulsion
  • 00:08:03
    between the
  • 00:08:04
    strands the Dome L's touching is at
  • 00:08:07
    thousands of volts so why isn't she
  • 00:08:09
    shocked as should be by handling a
  • 00:08:11
    faulty 110 volt light
  • 00:08:13
    socket the answer has to do with
  • 00:08:21
    energy voltage is energy per
  • 00:08:25
    charge Jews per Kum only a tiny fraction
  • 00:08:29
    of a kulum makes up the charge on the
  • 00:08:31
    generated Dome so a small amount of
  • 00:08:35
    energy per tiny amount of charge can
  • 00:08:37
    equal a huge
  • 00:08:39
    voltage so any energy transfer to luri
  • 00:08:42
    is
  • 00:08:43
    minuscule but that's not the case with a
  • 00:08:46
    faulty light socket the flow of charge
  • 00:08:48
    there is in kums not tiny fractions of
  • 00:08:52
    kums the flow of energy can be
  • 00:08:55
    fatal when thinking voltage think rati
  • 00:08:59
    IO of energy per
  • 00:09:01
    charge are you getting this I hope so
  • 00:09:05
    let me leave you with a concluding
  • 00:09:08
    question consider a pair of equally
  • 00:09:10
    charged particles separated by a certain
  • 00:09:14
    distance if exactly midway between these
  • 00:09:17
    particles their combined electric Fields
  • 00:09:20
    cancel to zero what can you say about
  • 00:09:23
    the signs of charge of the
  • 00:09:25
    particles are they like charges or
  • 00:09:28
    unlike charges
  • 00:09:30
    can you support your answer until next
  • 00:09:33
    time good
  • 00:09:37
    energy
Etiquetas
  • force field
  • gravitational field
  • electric field
  • vector
  • electrostatics
  • Van de Graaff generator
  • Coulomb's law
  • field lines
  • electric charge
  • field strength