Amplitude & frequency

Learning objectives:

• Periodic phenomena have both an amplitude and a frequency.
• The amplitude describes the maximum intensity.
• The frequency describes how often it happens.

A spring

The distance this spring moves is its amplitude.

The number of times it moves up and down over a given time period is its frequency. In this case, the spring moves up and down 13 times a minute.

A pendulum

The distance this pendulum moves back and forth is its amplitude.

The number of times that it swings back and forth in a given time is its frequency. This pendulum swings at a frequency of 22 times per minute.

Sine wave

Many phenomena can be described with a sine wave, including the movement of a spring or pendulum, as well as sound and light waves.

In the image above, the blue wave has a larger amplitude that the red wave. They both have the same frequency.

In the image above, the blue wave has a higher frequency than the red wave. They both have the same amplitude.

Examples of amplitude

• The distance a spring or pendulum moves
• The height a frog jumps
• The loudness of a sound
• The brightness of a light
• The strength of a heart beat
• The voltage of an electrical current

Examples of frequency

• The number of times a spring or pendulum moves up and down in 1 minute
• The number of times a frog jumps in 1 minute
• The pitch of a musical note
• The color of light
• A heart rate
• The frequency of an electrical current

Units of frequency

Frequency is often measured in cycles per second. This unit has a special name, Hertz, which is abbreviated Hz. 

Typical examples of frequency

Phenomenon	Frequency
Heart beat	60 beats per minute (1 Hz)
Alternating electrical current	60 cycles per second (60 Hz)
Lowest pitch a person can hear	20 Hz
Highest pitch a person can hear	20,000 Hz
Red light	1,000,000,000,000 Hz
Xrays	1,000,000,000,000,000,000 Hz