6.2 Describing Waves

16 October 2010

Write down two similarities between longitudinal and

transverse waves

Write down two differences

Give an example of each

Aims

• Introduce wavelength and amplitude for longitudinal and transverse waves

• Show that wavespeed depends on the medium and frequency depends on the source

• Introduce the wave equation

Amplitude, A

• The maximum distance that each point in the medium moves from its normal position as the wave passes

• Measured in metres, m

Frequency, f

• This is the number of waves that pass any point in the medium every second, so it is the same as the number of vibrations per second

• Frequency is measured in per seconds or hertz, 1/s, s-1 or Hz

Wave speed, v

• This is the speed at which each wave crest moves through the medium.

• Measured in metres per second, m/s or ms-1

Wavelength, λ

• This is the length of a complete wave measured from any point to the next identical point – the distance is always the same no matter which point you choose

• It is measured in metres, m

Can we figure the equation out?

Quantity Symbol Unit Symbol Relationship?

Speed

Frequency

Wavelength

Quantity Symbol Unit Symbol Relationship?

Speed vmetres per

secondm/s v = f λ

m/s = 1/s x mFrequency f Hz (1/s) 1/s

Wavelength λ metres m

Quantity Symbol Unit Symbol Relationship?

Speed

Frequency

Wavelength

Quantity Symbol Unit Symbol Relationship?

Speed

Frequency

Wavelength

Quantity Symbol Unit Symbol Relationship?

Speed

Frequency

Wavelength

Quantity Symbol Unit Symbol Relationship?

Speed

Frequency

Wavelength

fv Where:v = speed of wave / m/sf = frequency of wave / Hz (1/s)λ = wavelength of wave / m

How can we prove this?

1

1

330

330

msf

msv

fv

What would happen if we increased the wavelength of a wave?What would happen if we decreased the wavelength of a wave?