Topic 4 Waves

Question 1

What do waves do?

Answer 1

Waves transfer energy and information without transferring matter. Evidence of this for a water wave can be seen when a ball dropped into a pond bobs up and down, but the wave energy travels outwards as ripples across the surface of the pond.

Question 2

Waves key terms

Answer 2

Frequency- the number of waves passing a point each second, measured in hertz
Speed- measured in m/s
Wavelength- measured from peak to peak
Amplitude- half of the distance from the top to the bottom of the wave
Period- the time taken for one wavelength to pass a point

Question 3

What are longitudinal and transverse waves?

Answer 3

Longitudinal- sound waves and seismic p waves are longitudinal waves. The particles in the material the sound is travelling through move back and forth along the same direction that the sound is travelling
Transverse- waves on a water surface, electromagnetic waves and seismic S waves are all transverse waves. The particles of water move in a direction at right angles to the direction the wave is travelling

Question 4

What are the key wave equations?

Answer 4

Wave speed= frequency x wavelength
Wave speed= distance/ time

Question 5

How can you calculate the speed of sound in air?

Answer 5

Method: using an echo
1. Measure the distance from the source of the sound to the reflecting surface( the wall).
2. Measure the time interval, with a stopwatch, between the original sound being produced using the echo being heard
3. Use speed= distance/time to calculate the speed of sound in air

Question 6

How do calculate the speed of ripples on water surfaces?

Answer 6

You can calculate out of speed of ripples on the surface of water using a ripple tank and a strobe.

Question 7

Waves and boundaries

Answer 7

Waves can be:
-refracted
-reflected
-transmitted
-absorbed

Question 8

How can sound waves be move at a boundary?

Answer 8

• sound is transmitted through material when the densities are similar
• sound can be absorbed by materials. The amount of absorption depends on the material and the wavelength of the sound
• sound is reflected when there is a big difference in the densities of the materials at an interface, for example between air and concrete

Question 9

Refraction in waves

Answer 9

Refraction can result in a change of both speed and direction.
The direction does not change if the wavefronts travel perpendicular to the normal