3b: Properties of waves

waves

a way of transferring energy from place to place without matter by oscillations about a fixed point

two types of waves

- longitudinal
- transverse

transverse waves

waves where the points along its length vibrate at 90 degrees to the direction of energy transfer

features of transverse waves

- have peaks and troughs
- vibrate 90 degrees to the direction of energy transfer
- transfer energy but not particles
- cannot move in gas
- electromagnetic waves can move in a vacuum
- constant density and pressure

peak/crest

highest point on the wave above the rest position

trough

lowest point on the wave below the rest position

transverse waves - 4 examples

- ripples on water
- vibrations in a guitar string
- s-waves
- EM waves

longitudinal waves

waves where the points along its length vibrate parallel to the direction of energy transfer

features of longitudinal waves

- have compressions and rarefactions
- parallel to direction of energy transfer
- transfer energy but not particles
- move in all 3 states of matter
- cannot move in a vacuum
- changes in density and pressure

compressions

close together

rarefaction

far apart

longitudinal waves - 3 examples

- sound waves
- p-waves
- pressure waves

amplitude (A)

distance from the undisturbed position to the peak or trough of a wave

unit for amplitude

metres

wavelength

distance from one point on the wave to the same point on the next wave

wavelength - transverse waves

measured from one peak to the next peak

wavelength - longitudinal waves

measured from the centre of one compression to the centre of the next

symbol for wavelength

λ (lambda)

unit for wavelength

metres

frequency (f)

number of waves passing a point in a second

unit for frequency

hertz (Hz)

time period (T)

time taken for a single wave to pass a point

unit for time period

seconds

wavefronts

created by overlapping lots of different waves and represented by a line where all the vibrations are in phase and the same distance from the source

wavefront - ray

arrow showing the direction the wave is moving

wavefront - wavelength

space between each wavefront

wavefronts close together

short wavelength

wavefronts far apart

long wavelength

relationship between the speed, frequency and wavelength of a wave

wave speed = frequency x wavelength

unit for wave speed

m/s

relationship between frequency and time period

frequency = 1/ timeperiod

1 kHz to Hz

1 kHz = 1000 Hz

doppler effect

change in wavelength and frequency of a wave emitted by a moving source

doppler effect - wave source moving towards the observer

- observed frequency increases
- observed wavelength decreases

doppler effect - wave source moving away from the observer

- observed frequency decreases
- observed wavelength increases

reflection

a wave hits a boundary between two media and does not pass through, but instead stays in the original medium

refraction

a wave passes a boundary between two different transparent media and undergoes a change in direction

sound waves

vibration of air molecules

what happens to a sound wave when it comes into contact with a solid

vibrations transfer to the solid

are sound waves longitudinal or transverse

longitudinal

reflection of sound waves

echo

electromagnetic waves

transverse waves that transfer energy from the source of the waves to an absorber

properties of EM waves

- transverse
- travel through a vacuum at the same speed