Topic 4 - Waves Flashcards
Paper 1
What do waves transfer
Transfer energy and information without transferring matter
Describe evidence that with water and sound waves it is the wave and not the water or air that travels
Ripples on a water surface cause floating objects, such as twigs, to bob up and down, but not across the water.
A strummed guitar string creates sound waves that reach the ear without creating a vacuum by carry air.
Define frequency and what is it measured in
The number of waves produced by a source each second or the number of complete waves passing a certain point per second.
It’s measured in hertz (Hz) where 1 hertz is 1 wave per second.
Define wavelength and what is it measured in
The distance between the same point on two adjacent waves.
It’s measured in metres
Define amplitude
The maximum displacement of a point on the wave from its undisturbed/rest position
Define period
The amount of time it takes for a full cycle of the wave to be completed.
What equation links period and frequency
Period = 1/frequency
T=1/f
Define wave velocity
The speed of a wave in a certain direction
Define wavefront
Imaginary lines drawn through identical points on waves, eg. through each crest. They’re perpendicular to the direction in which the wave is moving.
What are the differences between longitudinal and transverse waves
Transverse waves oscillate at right angles to the direction that they travel/transfer energy
Longitudinal waves oscillate parallel to the direction that they travel/transfer energy. They have areas of rarefaction (low density of particles) and areas of compression.
Give examples of transverse waves
- All electromagnetic waves
- Ripples on water
- S-waves
Give examples of longitudinal waves
- Sound waves
- P-waves
What are the equations for wave speed/velocity
wave speed = frequency x wavelength
wave speed = distance/time
What symbol represents wavelength
λ
Describe how to measure the velocity of sound in air
- Set up two microphones next to a speaker, which is connected to an oscilloscope
- Move one microphone away from the speaker. Its trace will shift sideways on the oscilloscope.
- Keep moving it until the two traces on the oscilloscope are aligned once more, so measuring the distance between them would measure the wavelength
- Use the formula v=fλ to find the wave speed. The frequency can be found through the formula f=1/T
Describe how to measure the velocity of ripples on water surfaces
- Fill a ripple tank with water to a shallow depth
- Connect the dipper (which dips in and out of the water to produce ripples) to the signal generator and set it off at a known frequency
- Dim the lights and turn on the strobe light to see a wave pattern made by shadows of the wave crests on the screen below the tank
- Increase the frequency of the strobe light until the wave pattern on the screen appears to freeze and stop moving, because the frequency of the water waves and the strobe light are equal
- The average wavelength can be measured with a ruler and the formula v=fλ can be used to find the wave speed where f is set by the strobe light and signal generator
How can time and wave velocity be used to find distance/depth
Use the formula v=x/t
What happens to waves at a boundary
Reflection - the waves bay bounce back from the second material
Transmission - the waves may carry on travelling through the new material, but can undergo refraction
Adsorption - the waves may be absorbed by the second material. This transfers energy to the material’s energy stores, usually the thermal store
What happens during refraction
It occurs because waves travel faster in some materials than others, so the speed of a wave can change as it crosses a boundary between two materials
If a wave slows down, due to a denser material, at a boundary, it bends towards the normal
If a wave speeds up, due to less dense material, at a boundary, it bends away from the normal
