Properties of Waves Flashcards
All 29 cards in this deck
What do all waves transfer?
Energy and information, without transferring matter.
True or false? A sound wave carries air across the room from the speaker to your ear.
False. The sound wave transfers energy and information, but the air itself is not transferred.
What evidence shows that a water wave travels but the water itself does not?
e.g. ripples passing a duck floating on a pond
The duck bobs up and down on the spot; it is not carried along with the wave.
What is the frequency of a wave, and what unit is it measured in?
The number of complete waves passing a point each second, measured in hertz (Hz).
What is the wavelength of a wave, and what unit is it measured in?
The distance from one point on a wave to the same point on the next wave (e.g. crest to crest), measured in metres (m).
True or false? The amplitude of a wave is the distance from a crest to a trough.
False. Amplitude is measured from the rest position to a crest — half the crest-to-trough distance.
What is the period of a wave?
The time taken for one complete wave to pass a point. Linked to frequency by .
In a transverse wave, in which direction do the particles oscillate?
Perpendicular (at right angles, 90°) to the direction the wave travels.
In a longitudinal wave, in which direction do the particles oscillate?
Parallel to the direction the wave travels (back and forth), making compressions and rarefactions.
Give two examples of transverse waves other than water waves.
Electromagnetic waves (e.g. light, microwaves, X-rays) and seismic S-waves.
True or false? Sound waves are transverse waves.
False. Sound waves are longitudinal.
What is the wave equation linking wave speed, frequency and wavelength?
— wave speed (m/s) = frequency (Hz) × wavelength (m).
How many hertz are there in 1 kHz and in 1 MHz?
1 kHz = 1000 Hz; 1 MHz = 1 000 000 Hz.
True or false? To get a wave speed in m/s from , the wavelength must be in metres.
True. Frequency is in Hz and wavelength in m, so a wavelength in cm must be converted first.
What is the equation linking wave speed, distance and time?
— wave speed (m/s) = distance (m) ÷ time (s).
How can you measure the speed of sound in air?
Measure a long distance (e.g. 100 m) between a sound source and an observer, time how long the sound takes to travel it, then use speed = distance ÷ time.
How can you measure the speed of ripples in a ripple tank by timing?
Time how long one wavefront takes to travel a measured distance across the tank, then use wave speed = distance ÷ time.
True or false? Measuring the wavelength of ripples on its own is enough to find their wave speed.
False. You also need a time: use speed = distance ÷ time, or measure the frequency and use .
What is refraction?
The change in direction of a wave when it crosses a boundary between two different materials.
What is the angle of refraction?
e.g. a light ray entering a glass block
The angle between the refracted ray (inside the glass) and the normal.
What is the normal on a ray diagram?
A line drawn at right angles (90°) to the boundary at the point where the ray meets it.
True or false? A light ray passing from air into glass bends away from the normal.
False. It bends towards the normal on entering the glass.
How do you measure the wavelength of ripples in a ripple tank?
Use a strobe light or a photo so the ripples look still, measure the distance across several wavelengths (e.g. 10 gaps between ripples), then divide by the number of wavelengths.
How do you measure the frequency of ripples in a ripple tank?
Count the number of ripples passing a fixed point in a measured time, then frequency = number of waves ÷ time.
What happens to the direction of a wave that meets a boundary along the normal (at 90° to the surface)?
Its direction doesn't change. It carries straight on into the new material.
What is the angle of incidence?
e.g. a light ray hitting a glass block
The angle between the ray arriving at the boundary and the normal.
When a metal rod is tapped with a hammer, how does the wavelength of the peak-frequency wave in the rod compare with the rod's length?
The wavelength is twice the length of the rod.
Are seismic P-waves transverse or longitudinal?
Longitudinal.
How is the wavelength of a longitudinal wave measured?
e.g. a sound wave
From the middle of one compression to the middle of the next compression (or from one rarefaction to the next).