Representing longitudinal waves
I can interpret and sketch graphs of longitudinal waves.
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Lesson details
Key learning points
- In a longitudinal wave, the oscillations / vibrations are in the same direction in which the wave travels.
- Displacement is the distance one part of a wave is moved away from its rest position.
- In a longitudinal wave, forwards displacement is positive and backwards displacement is negative.
- Wavelength of a longitudinal wave is the distance between one compression (or rarefaction) and the next.
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.
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).
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.How does a loud speaker move to make a sound wave that moves forwards?
Q2.How do air particles move as a sound wave moves forwards through the air?
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?
Q5.What is the maximum displacement of a particle in a wave called?
Q6.What is the name given to the number of complete wave cycles passing a point each second?
Assessment exit quiz
6 Questions
Q1.How do particles in a soundwave move?
Q2.How far do the particles in a soundwave vibrate?
Q3.What is the amplitude of a longitudinal wave?
Q4.What is the distance between two wave crests on a displacement-distance graph equal to?
