Physics Education: Sound & Radio Wave Calculations Explained (Stuart Method)

00:06:49
https://www.youtube.com/watch?v=OdpVee5Meik

概要

TLDRThe video discusses the wave equation v = f * λ, illustrating how wavelength (λ), frequency (f), and speed (v) are interconnected. It demonstrates calculations for different waves, such as sound and radio waves, highlighting how changes in frequency and wavelength affect wave speed. For instance, it shows that a sound wave with a frequency of 170 Hz and a wavelength of 2 meters travels at 340 meters per second, while a radio wave with a frequency of 3 megahertz and a wavelength of 100 meters travels at 300 million meters per second. The video emphasizes that all types of waves, including sound, light, and microwaves, conform to this wave equation.

収穫

  • 🔹 The wave equation is v = f * λ.
  • 🔹 Doubling frequency halves wavelength.
  • 🔹 Sound waves travel at 340 m/s at 170 Hz.
  • 🔹 Radio waves travel at 300 million m/s.
  • 🔹 3 million Hertz = 3 megahertz.
  • 🔹 It takes 13 mins for radio waves to reach Mars.
  • 🔹 We can't hear radio waves directly.
  • 🔹 Minimum frequency for sound detection is 20 Hz.
  • 🔹 Changes in frequency affect wavelength directly.

タイムライン

  • 00:00:00 - 00:06:49

    The video explains the wave equation v = f * λ, connecting wavelength, frequency, and speed. It demonstrates calculations using examples of both a wave with a frequency of 2 Hertz and a wavelength of 5 meters, resulting in a speed of 10 meters per second. Doubling the frequency to 4 Hertz while maintaining the speed at 10 meters per second yields a new wavelength of 2.5 meters. The video further explores sound waves, emphasizing that they require a frequency of at least 20 Hz for human detection. An example with a frequency of 170 Hz and a wavelength of 2 meters is presented, calculating the wave speed to be 340 meters per second. This speed is compared to that of a jet plane. Lastly, radio waves are examined, with a frequency of 3 million Hertz (3 MHz) and a wavelength of 100 meters, resulting in a speed of 300 million meters per second. The delay in communication with the moon and Mars is mentioned, highlighting that radio waves need conversion into sound waves to be heard.

マインドマップ

ビデオQ&A

  • What is the wave equation?

    The wave equation is v = f * λ, where v is speed, f is frequency, and λ is wavelength.

  • What is the speed of a sound wave with a frequency of 170 Hz and a wavelength of 2 meters?

    The speed of the sound wave is 340 meters per second.

  • How fast do radio waves travel?

    Radio waves travel at a speed of 300 million meters per second (or 300,000 km/s).

  • Why can't we hear radio waves?

    Radio waves must be picked up by a radio antenna and converted into sound waves for us to hear.

  • What happens to wave speed if frequency is doubled?

    If frequency is doubled while keeping speed the same, the wavelength is halved.

  • What is the minimum frequency for human detection of sound waves?

    The minimum frequency for human detection of sound waves is 20 Hz.

  • How long does it take for radio waves to reach Mars?

    It takes about 13 minutes for radio waves to reach Mars.

  • What is 3 million Hertz also known as?

    3 million Hertz is also known as 3 megahertz.

  • How does wavelength change if the frequency is increased?

    If frequency increases and speed remains constant, wavelength decreases.

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  • 00:00:03
    [Music]
  • 00:00:08
    the previous video showed how the
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    wavelength lambda which is the distance
  • 00:00:14
    between crests the frequency F which is
  • 00:00:19
    the number of waves per second and the
  • 00:00:26
    speed V are all connected through the
  • 00:00:33
    wave equation
  • 00:00:35
    v equals if lambda
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    with a two Hertz wave which has a
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    wavelength of five meters
  • 00:00:48
    what's its speed
  • 00:00:54
    easy as pie
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    just make F equal to Hertz and lambda
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    five meters and multiply them
  • 00:01:08
    traveling at ten meters per second
  • 00:01:16
    let's double the frequency to four Hertz
  • 00:01:19
    but keep the speed the same
  • 00:01:24
    what's the new wavelength
  • 00:01:31
    piece of cake make F for Hertz and keep
  • 00:01:37
    the speed at 10 meters per second
  • 00:01:42
    dividing both sides by four eliminates
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    it from the right-hand side
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    leaving lambda on its own
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    the new wavelength is 2.5 meters half
  • 00:02:00
    its previous length
  • 00:02:07
    now let's try the wave equation on a
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    sound wave
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    the animation shows how the vibrating
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    sauce
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    bunches up and spreads out the air
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    molecules at different times
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    soundwaves need to have a frequency of
  • 00:02:28
    at least 20 waves per second in order to
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    be detected by our ears
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    but this one is slowed down to just a
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    few Hertz so we can follow it more
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    easily with our eyes
  • 00:02:43
    now let's try a sound wave with a
  • 00:02:46
    frequency of a hundred and seventy Hertz
  • 00:02:48
    and a wavelength of two meters
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    that means a hundred and seventy sound
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    waves are hitting your eardrums each
  • 00:03:01
    second and two meters apart
  • 00:03:07
    the sound tone is doing that to your
  • 00:03:09
    ears right now
  • 00:03:17
    what's the speed of the wave
  • 00:03:26
    - easy
  • 00:03:31
    we just make if 170 Hertz and lambda2
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    meters
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    apply them
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    the sound waves are coming at you at the
  • 00:03:43
    speed of 340 meters per second
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    that's why faster than a jet plane
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    draw this one
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    what's the speed of a radio wave which
  • 00:04:09
    has a wavelength of 100 meters and a
  • 00:04:12
    frequency of 3 million Hertz
  • 00:04:19
    [Music]
  • 00:04:23
    by the way three million Hertz can also
  • 00:04:27
    be called three megahertz
  • 00:04:33
    substitute 3 million Hertz for if
  • 00:04:39
    and 100 meters for lambda
  • 00:04:45
    it just means to give it the value of
  • 00:04:50
    multiplying them gives a speed of 300
  • 00:04:53
    million meters per second
  • 00:04:59
    or 300,000 km/s
  • 00:05:07
    think about that
  • 00:05:10
    that's fast
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    it's so fast that radio waves can travel
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    to the moon in one second
  • 00:05:19
    [Music]
  • 00:05:21
    this would cause delays in a moon phone
  • 00:05:24
    call but not much
  • 00:05:27
    however it takes radiowaves 13 minutes
  • 00:05:31
    to reach Mars
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    and an hour and 20 minutes to 7:00
  • 00:05:44
    that would be a seriously long haul
  • 00:05:52
    actually we can't hear radio
  • 00:05:55
    their ears
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    instead we need them to be picked up by
  • 00:06:00
    a radio antenna and convert them into
  • 00:06:03
    sound waves
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    which our ears can hear
  • 00:06:07
    [Music]
  • 00:06:14
    waves sound waves water waves light
  • 00:06:19
    waves and microwaves
  • 00:06:23
    all obey the wave equation
  • 00:06:28
    will show this in more depth in the next
  • 00:06:30
    video
  • 00:06:35
    [Music]
  • 00:06:40
    [Music]
タグ
  • wave equation
  • wavelength
  • frequency
  • wave speed
  • sound waves
  • radio waves
  • Hertz
  • calculations
  • physics
  • waves