What is Wavelength and Frequency?

Wavelength -> Simply the length of any wave.

Examples of waves: Ocean waves travelling through water, sound waves travelling through air, light waves etc..

Let us take the case of  ocean wave -  its wavelength is the distance from the top of one wave (called crest) to the top of the next wave. We can also measure the distance from the lowest point between two waves (called trough) to the next trough. We would get the same distance either way.

The wavelengths of ocean waves we see at the beach are usually 10 or so meters (33 feet) or longer. Sound waves that humans can hear have wavelengths between about 2 cm (an inch) and 17 meters (56 feet). Waves of electromagnetic radiation that we see as light have really, really short wavelengths between 400 and 700 nanometers (a nanometer= 1 billionth of a meter).

Frequency -> measure of the number of waves/second

The frequency of a wave depends on:

1. How fast the wave is moving.
2. It also depends on the wavelength of the wave

Imagine two sets of waves that have the same speed. If one set has a longer wavelength, it will have a lower frequency (more time between waves). If the other set has a shorter wavelength, it will have a higher frequency (less time between waves).

Sound waves with a wavelength around 34 cm have a frequency of 1,000 hertz. A hertz is one wave per second. So a thousand sound waves can enter your ear in a second! Sound waves travel much faster than normal water waves. Sound waves move through the air at around 343 meters/second (767 miles/hour).

Light moves even faster and has shorter wavelengths. These combine to give light, extremely high frequencies.

The frequency of the wave determines its color: 4×10¹⁴ Hz is red light, 8×10¹⁴ Hz is violet light, and between these (in the range 4-8×10¹⁴ Hz) are all the other colors of the rainbow. An electromagnetic wave can have a frequency less than 4×10¹⁴ Hz, but it will be invisible to the human eye; and is termed as infrared (IR) radiation.