New
New
Year 10
AQA
Higher

# Representing longitudinal waves

I can interpret and sketch graphs of longitudinal waves.

New
New
Year 10
AQA
Higher

# Representing longitudinal waves

I can interpret and sketch graphs of longitudinal waves.

Share activities with pupils
Share function coming soon...

## Lesson details

### Key learning points

1. In a longitudinal wave, the oscillations / vibrations are in the same direction in which the wave travels.
2. Displacement is the distance one part of a wave is moved away from its rest position.
3. In a longitudinal wave, forwards displacement is positive and backwards displacement is negative.
4. Wavelength of a longitudinal wave is the distance between one compression (or rarefaction) and the next.

### Common misconception

Particles in a longitudinal wave move forward and backward between one compression and the next.

Demonstrate the movement of a candle flame in front of a loudspeaker set to a very low frequency with a wavelength of about 30 m (at 10 Hz).

### Keywords

• Longitudinal wave - each part of a longitudinal wave oscillates forward and backward in the same direction in which the wave moves.

• Compression - part of a longitudinal wave in which parts of the wave are squashed closer together is called a compression.

• Rarefaction - part of a longitudinal wave in which parts of the wave are spaced further apart is called a rarefaction.

• Wavelength - the wavelength of a longitudinal wave is the distance along the wave between one compression and the next.

• Amplitude - the amplitude of a longitudinal wave is the maximum distance each part of the wave moves forward or backward.

Use a slinky spring to demonstrate longitudinal waves. Tie a piece of string around one turn of coil to show how each part of the spring moves as the wave travels forwards.
Teacher tip

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
How does a loud speaker move to make a sound wave that moves forwards?
up and down
side to side
Q2.
How do air particles move as a sound wave moves forwards through the air?
side to side
forwards with the wave
Q3.
A sound wave is an example of a wave.
Q4.
What is the wave medium of a longitudinal wave travelling along a spring stretched across a table?
the air
the table
Q5.
What is the maximum displacement of a particle in a wave called?
wavelength
period
frequency
Q6.
What is the name given to the number of complete wave cycles passing a point each second?
period
displacement
amplitude

## Exit quiz

### 6 Questions

Q1.
How do particles in a soundwave move?
Correct answer: they oscillate backwards and forwards and do not move along the wave
they oscillate backwards and forwards as they move along the wave
they move along the wave without oscillating
Q2.
How far do the particles in a soundwave vibrate?
they vibrate between one end of the wave and the other
they vibrate between one compression and the next
Correct answer: they vibrate less than the distance between one compression and the next
Q3.
What is the amplitude of a longitudinal wave?
the distance between two compressions
Correct answer: the maximum displacement of the wave
the distance between a compression and a rarefaction
the wavelength of the wave
Q4.
What is the distance between two wave crests on a displacement-distance graph equal to?
the amplitude
the frequency
the period