2015 EdExcel A Level Physics Topic 5 · 2018-09-18 · 2015 EdExcel A Level Physics Topic 5 Waves...
Transcript of 2015 EdExcel A Level Physics Topic 5 · 2018-09-18 · 2015 EdExcel A Level Physics Topic 5 Waves...
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2015 EdExcel A Level PhysicsTopic 5
2015 EdExcel A Level PhysicsTopic 5
Waves Introduction
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What is a wave?
A wave is a phenomenon in which energy is transferred through vibration
There is no transfer of matter in a wave, just energy
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Crests and Troughs
A crest is the highest point in the wave
A trough are the lowest point in the wave
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Describing Waves
The height of a crest or depth of
trough is the Amplitude
(maximum displacement
measured from the equilibrium
position).
Wavelength () is the distance
between two successive crests or
troughs.
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Describing Waves
Frequency is the number of vibrations or complete cycles in one second, passing a point or emitted from a source.
Time Period is the time taken for one complete vibration (or oscillation or cycle)
The SI Unit For Period is second (s).
The SI Unit for Frequency is Hertz (Hz)
1 Hz is 1 vibration in 1 second.
50 Hz is 50 vibrations in 1 second.
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Wave speed
Wave speed is simply distance travelled per second.
The SI unit of speed is m/s
Examples of wavespeeds:Light (vacuum) 3x108m/sSound (air) 330m/s
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Labelling a wave
0 1 2
5
-5
Amplitude=?Time period=?Frequency=?
time (s)
y(m)
3
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Labelling a wave
0 1 2
5
-5
Amplitude=5mTime period=2sFrequency=0.5Hz
time (s)
y(m)
3
amplitude
Time period
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The Wave Equation
The wave equation relates the speed of the wave to its
frequency and wavelength:
Wave speed (v) = frequency (f) x wavelength ()
in ms-1 in Hz in m
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Example
V=1m/s 11m
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Example
V=1m/s 11m
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Wave equation practice questions
1) A water wave has a frequency of 3Hz and a wavelength of
0.6m. How fast is it moving?
2) A water wave travels through a pond with a speed of 2ms-1
and a frequency of 10Hz. What is the wavelength of the
waves?
3) The speed of sound is 330ms-1 (in air). When Tom hears
this sound his ear vibrates 440 times a second. What was
the wavelength of the sound?
4) Violet light has a wavelength of around 6x10-7m. What is
the frequency of violet light?
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Wave equation practice questions
1) A water wave has a frequency of 3Hz and a wavelength of
0.6m. How fast is it moving?
2) A water wave travels through a pond with a speed of 2ms-1
and a frequency of 10Hz. What is the wavelength of the
waves?
3) The speed of sound is 330ms-1 (in air). When Tom hears a
sound his ear vibrates 440 times a second. What was the
wavelength of the sound?
4) Violet light has a wavelength of around 6x10-7m. What is
the frequency of violet light?5x1014Hz
0.75m
0.2m
1.8m/s
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Types of Waves
1) Mechanical Waves need matter (medium) to travel through
2) Electromagnetic Waves can travel through empty space.
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1) Mechanical Waves
water
air
solids
Mechanical waves travel through mediums
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1) Mechanical Wavesi) transverse
ii) longitudinal
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i) TransverseMost waves are transverse
The vibrations in transverse waves go from side to side.
The vibrations are perpendicular to the
direction the wave is travelling in
(moving at a 90o to direction)
AmplitudeWavelength
Trough
Crest
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ii) Longitudinal
In longitudinal (compression) waves, energy moves along the medium whilst travelling forwards.
Wavelength
compression
rarefaction
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Graph of a longitudinal wave
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Core Practical 6 – Speed of sound in air
Determining the speed of
sound in air using a 2
beam oscilloscope, signal
generator, speaker and
microphone
A pulse is sent directly to
the oscilloscope and a
second pulse from the
microphone, detecting the
sound wave from the
loudspeaker.
Oscilloscope
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Core Practical 6 – Speed of sound in air
As the microphone is
moved away from the
loudspeaker speaker the
phase difference changes
The distance moved from
in phase position to the
next in phase position is
measured. This distance is
equal to the wavelength.
The frequency is found
using the timebase (time
per division) and f=1/t
Oscilloscope