Amplitude

Amplitude tells us how strong or intense a wave is. It measures how far the particles of the medium move from their mean (rest) position during a wave. A larger amplitude means bigger vibrations, and a smaller amplitude means gentler vibrations.

I like to think of amplitude as the ‘height’ or ‘size’ of the wave’s disturbance.

Definition: Amplitude is the maximum displacement of particles from their mean position when a wave passes through a medium.

It is usually represented by the letter \( A \).

In a transverse wave, particles move up and down. The amplitude is the vertical distance from the mean line to the crest (highest point) or trough (lowest point).

In longitudinal waves, like sound waves, particles move back and forth. Amplitude represents how much the particles are pushed together or pulled apart.

Amplitude directly influences the energy of a wave. Higher amplitude means the wave carries more energy.

For example:

• Louder sound → higher amplitude.
• Brighter light → higher amplitude of the electromagnetic wave.
• Bigger water waves → larger amplitude.

The frequency or speed might stay the same, but the energy can still increase simply by increasing amplitude.

In many wave equations, amplitude appears as a constant in front of the sine or cosine function. For example, a simple wave may be written as:

Here, \( A \) tells how large the oscillations are.

Here are some everyday situations where amplitude plays a clear role:

• Turning up the volume of a speaker increases the amplitude of sound waves.
• Dropping a stone from a greater height creates larger water wave amplitude.
• Striking a drum harder increases the amplitude of vibrations and produces a louder beat.

In each case, the strength of the wave increases because amplitude increases.