Period of a Wave

The period of a wave tells us how long it takes for one complete wave cycle to pass a fixed point. If you watch a wave pattern at a spot, the time between two crests passing you is the period.

I like to think of period as the ‘time for one repeat’ of the wave’s motion.

Definition: The period of a wave is the time taken to complete one full cycle of the wave.

It is represented by the symbol \( T \) and is measured in seconds (s).

The period can be seen clearly when you observe repeating points of a wave:

• In a transverse wave: the time between two crests passing a point.
• In a longitudinal wave: the time between two compressions passing the same point.

Even though the patterns look different, the idea behind the period remains the same — the time between repeating features.

Period and frequency are closely related. Frequency tells how many cycles occur per second, while period tells how long one cycle lasts. They are exact opposites of each other.

The relation is:

So:

• High frequency → short period.
• Low frequency → long period.

The meaning of period does not change depending on the type of wave. In all cases, it is simply the time required for the wave pattern to repeat at a point.

The period influences how a wave interacts with objects and how it carries energy. For example:

• A small period (high frequency) creates rapid vibrations.
• A large period (low frequency) produces slow, gentle repetitions.

Sound with a small period has a high pitch, while sound with a large period has a deep pitch.

You can feel or observe the period of waves in many everyday situations:

• The time gap between two ocean waves hitting the shore.
• The time between two loudspeaker vibrations during a bass note.
• The time between two pulses in a slinky oscillation.
• The flashing rate of a blinking light (each flash cycle has a period).

In each case, the period tells you how long one cycle takes before the pattern repeats.