6.1. Waves - wave properties

Question 1

what is the amplitude of a wave

Answer 1

height of the wave
measured from the centre line to the crest, or from the centre line to the trough

Question 2

how to measure the amplitude of a wave

Answer 2

from the middle of the wave to the crest or the trough

Question 3

what is the wavelength

Answer 3

the distance between the same point on two adjacent waves e.g. between the trough of one wave and the trough of the wave next to it

Question 4

what is the frequency

Answer 4

The number of complete waves passing a certain point per second

Question 5

what is frequency measured in

Answer 5

Hz (one wave per second)

Question 6

what is the top of a wave called

Answer 6

crest

Question 7

what is the bottom of a wave called

Answer 7

trough

Question 8

what is the period of a wave

Answer 8

The amount of time it takes for a full cycle of the wave

Question 9

formula for frequency and period

Answer 9

Period = 1/frequency

Question 10

what is the period of a wave measured in

Answer 10

seconds

Question 11

what are transverse waves

Answer 11

waves in which the oscillations are perpendicular to the direction of energy transfer

Question 12

examples of transverse waves

Answer 12

all electromagnetic waves e.g. light
ripples and waves in water

Question 13

what are longitudinal waves

Answer 13

waves in which the oscillations are parallel to the direction of energy transfer

Question 14

examples of longitudinal waves

Answer 14

sound waves in air
shock waves e.g. some seismic waves

Question 15

what is wavespeed

Answer 15

the speed at which energy is being transferred, or the speed the wave is moving at

Question 16

wave equation

Answer 16

Wave speed = frequency x wavelength (v=fλ)

Question 17

explain the experiment on how to use an oscilloscope to measure the speed of sound

Answer 17

Set up the oscilloscope so the detected waves at each microphone are shown as separate waves, allowing them to be compared.

Start with both microphones next to the speaker so they detect the same point in the wave cycle, meaning the two waves on the oscilloscope are aligned. Then slowly move one microphone away — as it gets further from the speaker it detects the wave later, shifting its wave out of alignment on the display. Keep moving it until the waves are aligned again, but have moved exactly one wavelength apart.

Measure the distance between the microphones — because the moved microphone is now exactly one full wavelength further away (the distance after which the wave pattern repeats), this distance equals one wavelength.

Use the formula v=fλ to find the speed of sound waves passing through the air — the frequency is whatever you set the signal generator to, and the wavelength was just measured.

The speed of sound in air is around 330 m/s, so check your results roughly agree.

Question 18

when using an oscilloscope to measure the speed of sound, why is it important to have a signal generator attached to the speaker

Answer 18

so you can generate sounds with a specific frequency

Question 19

how to measure the speed of water ripples using a lamp

Answer 19

1. using a signal generator attached to the dipper of a ripple tank you can create water waves at a set frequency
2. use a lamp to see wave crests on a screen below the tank. make sure the size of the waves’ shadow are the same size as the waves
3. the distance between each shadow line is equal to one wavelength. measure the distance between shadow lines that are 10 wavelengths apart, then divide this distance by 10 to find the average wavelength
4. use v=fλ to calculate the wave speed of the waves
5. this set up is suitable for investigating waves, because it allows you to measure the wavelength without disturbing the waves

Question 20

how to use the wave equation for waves on strings

Answer 20

1. set up a signal generator, a vibration transducer, a string connected to a pulley system with masses attached on a bench. then turn on the signal generator and vibration transducer. the string will start to vibrate
2. adjust the frequency of the signal generator until there’s a clear wave on the string. the frequency needed depends on the length of string between the pulley and the transducer, and the masses used
3. measure the wavelengths of these waves. the best way to do this is by measuring the lengths of 4 half-wavelengths in one go, and then divide to get the mean half-wavelength. then double this to get a full wavelength
4. the frequency of the wave is whatever the signal generator is set to
5. find the wavespeed using v=fλ