Frequency

Frequency tells us how often a wave repeats itself. If a wave pattern keeps passing a point again and again, frequency counts how many complete waves pass in one second. It’s basically the ‘speed of repetition’ of a wave.

I like to think of frequency as the rhythm of the wave — a fast rhythm means a high frequency, and a slow rhythm means a low frequency.

Definition: Frequency is the number of complete wave cycles passing a fixed point in one second.

It is denoted by \( f \) and is measured in hertz (Hz), where:

Regardless of the type of wave, frequency always describes how many complete oscillations the wave performs in one second.

For different waves:

• Transverse waves: number of crests passing a point per second.
• Longitudinal waves: number of compressions passing a point per second.

The patterns are different, but the idea of frequency stays the same.

Frequency is closely related to the time period (T), which is the time for one complete wave.

The relation is:

Frequency also connects to wavelength and wave speed through the formula:

Here are some simple ways to picture frequency in daily life:

• If water waves hit a rock 5 times per second, the frequency is 5 Hz.
• If a guitar string vibrates quickly, it produces a high-frequency (high-pitched) sound.
• If the vibrations are slow, the frequency is lower and the pitch is deeper.
• In light waves, violet light has higher frequency than red light.

Frequency helps explain why different sounds and colours feel different to our senses.

Frequency decides many important properties of waves:

• Pitch of sound.
• Colour of light.
• Energy of electromagnetic waves (higher frequency → more energy).
• How waves interact, interfere, and create patterns.

Once the idea of frequency is clear, understanding wave behaviour becomes much simpler.