What are Crest and Trough in a Wave?

When studying Physics (Sound and Waves), you will learn about 'Transverse Waves' (like light waves, or the ripples on the surface of water). The highest and lowest points of these waves are called the crest and trough.

Question (Click to Flip)

What happens if the crest of one wave hits the trough of another wave?

Answer

If a crest of exactly the same size meets a trough perfectly, they cancel each other out, resulting in a flat line. This phenomenon is called 'Destructive Interference' (used in noise-canceling headphones).

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Key Facts

Crests and Troughs only exist in 'Transverse waves' (where particles move up and down).

In 'Longitudinal waves' (like sound waves in air, where particles move left and right), the equivalents are 'Compressions' (high pressure) and 'Rarefactions' (low pressure).

1. What is a Crest?

Imagine a calm, flat surface of water (the resting position or equilibrium line). When a wave moves through the water, it pushes the water upwards.

The Crest is the absolute highest point of a wave above the resting position.
It represents the maximum positive displacement of the wave.

2. What is a Trough?

After the water goes up, it comes crashing down, dipping below the flat resting line.

The Trough is the absolute lowest point of a wave below the resting position.
It represents the maximum negative displacement of the wave.

3. Importance of Crest and Trough

These two points help physicists measure vital properties of a wave:

Amplitude: The distance from the flat resting line up to the crest (or down to the trough) is called the Amplitude. It determines how loud a sound is or how bright a light is.
Wavelength ($\lambda$): The horizontal distance measured exactly from one Crest to the next adjacent Crest (or from one Trough to the next Trough) is called the Wavelength.

Questions and Answers

What happens if the crest of one wave hits the trough of another wave?+

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