Waves Flashcards
How do longitudinal waves oscillate? Draw a diagram.
In the same direction as the direction in which the wave transfers energy.
How do transverse waves oscillate? Draw a diagram.
Perpendicular to the direction in which energy is transferred by the wave.
Give 3 examples of longitudinal waves.
Sound waves, ultrasound waves and seismic P waves.
Give 3 examples of transverse waves.
EM waves Light (an EM wave in itself) Seismic P waves Water waves
Which label represents the amplitude of the wave?
N
Which label represents the wavelength of the wave?
V, F
Which label represents the time period of the wave?
V, F
What does T represent?
A crest
What does E represent?
A trough
Define amplitude
The maximum displacement of a wave above the equilibrium (the maximum distance from the rest to the crest of a wave)
What is amplitude measured in?
It depends on the type of wave (e.g. water wave = m, sound wave = Pa)
Define wavelength (λ)
The distance between one crest and the next
What is wavelength measured in?
m (metres)
Define time period (T)
The time take for one complete wave cycle to pass a given point
What is time period measured in?
s (seconds)
Define frequency
The number of complete wave cycles that pass a given point per unit time/per second
What is frequency measured in?
Hz (hertz)
What is the relationship between frequency and time period?
f = 1 / T
(frequency (Hz) = 1 / time period (s))
What is the relationship between wave speed, frequency and wavelength?
v = fλ
(wave speed (m/s) = frequency (Hz) x wavelength (m))
Which 2 properties do all waves have in common?
They can all be refracted and reflected
What is a wave?
A oscillating disturbance which transfers energy and information without transferring matter.
What is another name for an oscillation?
A vibration
Define a rarefaction.
A reduction in the density of a wave.
For example: a sound wave moving through air is made up of alternating areas of higher and lower density. The areas of lower density are called rarefactions.
What is the speed at which all EM waves travel? What do we call this speed?
3 x 10^8 m/s
300 000 000 m/s
This is the ‘speed of light’.
What is this effect known as?
The Doppler Effect
What is the Doppler Effect?
The observed change in frequency and wavelength of a wave when its source is moving relative to an observer.
Give 6 properties which all EM waves possess.
They all…
can be reflected
can be refracted
travel at the speed of light
all transverse waves
all transfer energy and information without transferring matter
can all travel through a vacuum
Why does the Doppler Effect occur?
The speed of a wave is constant, therefore when the speed of the source increases, it ‘catches up’ to the wavefronts ahead, causing them to bunch up, and moves away from those behind, causing them to spread out.
An ambulance is moving towards a girl standing by the side of a road. As it gets closer, she notices that the pitch of the sound seems to change. What is this change? Why?
She notices that the pitch of the sound seems to increase.
This is because pitch is the sensation of frequency, and the frequency appears to increase due to the Doppler effect: the wavelength of the wave appears to decrease as it moves towards her. Since f = v/λ, and the speed of the wave remains constant, the frequency must increase.
An ambulance is moving away from a boy standing by the side of a road. As it gets further away, he notices that the pitch of the sound seems to change. What is this change? Why?
He notices that the pitch of the sound seems to decrease.
This is because pitch is the sensation of frequency, and the frequency appears to decrease due to the Doppler effect: the wavelength of the wave appears to increase as it moves away from him. Since f = v/λ, and the speed of the wave remains constant, the frequency must decrease.
Draw a graph of how perceived frequency varies as the source of a sound moves towards, passes, then moves away from an observer.
Define a wavefront.
Draw a diagram to illustrate your answer.
An imaginary plane which connects adjacent points on waves which are moving in phase (oscillating together), and is repeated every wavelength.
