# Frequency of a wave

The frequency of a wave is the number of vibrations in a given time.

The unit of time that we use to see how often a particle vibrates is the second.

If a particle vibrates 100 times every second, the frequency is 100 vibrations or 100 cycles per second.

### Unit of frequency

The unit of frequency is the Hertz and the symbol is Hz. It is named after Heinrich Rudolf Hertz who demonstrated radio waves in 1886.

1 cycle per second is equal to 1 Hertz.

5 cycles per second is 5 Hertz

For higher frequency, the kilohertz, the megahertz, or the gigahertz are used.

1 kilohertz  = 1000 Hertz = 1000 cycles per second

The frequency of AM radio waves is measured in kilohertz.

If the frequency at a specific station is 15 kilohertz, this means that the electrons in the antenna of the radio station are forced to vibrate 15000 times every second.

1 megahertz = 1 million Hertz = 1000000 Hertz = 1000000 cycles per second

The frequency of FM radio is measured in megahertz

1 gigahertz = 1 billion Hertz = 1000000000 Hertz = 1000000000 cycles per second.

The frequency of a radar or a microwave is measured in gigahertz

#### Frequency of a wave and the period

The pediod of a wave is the time it takes to complete just 1 vibration or 1 cycle.

If the frequency of a wave is 5 Hertz, we know that this means 5 cycles every second.

If 5 cycles are completed every second, then 1 cycle is completed every 1/5 second. The period is 1/5.

Generally speaking, the period is the inverse of the frequency.

Period  =  1 / frequency

By the same token, the frequency is the inverse of the period.

Frequency = 1 / period

Below, we show you a frequency of 1 cycle every 2 second.

Notice that 1 cycle is when you start at a maximum displacement of 10 cm and then reaches that maximum displacement of 10 cm again.

In other words, it takes 2 second to see another crest.

For a pendulum, the first crest on the left is the maximum displacement you pull it before releasing it. Then, it will take 2 seconds to go back to that same maximum displacement.

## Recent lesson

1. ### Law of Reflection

Mar 16, 17 03:15 PM

Great lesson about the law of reflection. Crystal clear explanation