Albert Teen YOU ARE LEARNING:  Speed of Wave  # Speed of Wave ### Speed of Wave

The speed of a wave is given by wavelength x frequency.

Waves are the transfer of energy. This transfer happens over a distance at a certain speed (v).

How do you calculate speed (v)? The speed of a wave can be calculated with its frequency (f) and wavelength (λ). What is the frequency of a wave? What is the SI unit for measuring the wavelength $(\lambda)$ of a wave? What is the unit for speed (v)? Now let's have a go at deriving the equation for the speed of a wave. We will do this, using wavelength and frequency.

1

We derived the SI unit for frequency from its equation. What is this? Remember Hertz is not the SI unit. 2

What is the SI unit for wavelength? 3

So, we know that the unit for speed is $^m/_s$ . This can also be written as $m\times \frac{1}{s}$ . Notice these are the two units for wavelength and frequency. So which one of these options if the correct formula for speed of a wave?

A: $speed = \frac{wavelength}{frequency}$

B: $speed=wavelength \times frequency$ What is the equation for speed? Given that wavelength (λ) is measured in metres $(m)$ , frequency (f) is measured in Hertz or $\frac{1}{s}$ , and speed (v) is measured in $^m/_s$ . So the speed of a wave is given by $v=f\times\lambda$ where v is speed, f is frequency, and λ is wavelength.

What is the speed of a wave that has a frequency of 20 Hz and a wavelength of 250m? The speed of sound in air is $343m/_s$ What is the wavelength of a sound wave with a frequency of $49Hz$ ? What is the frequency of red light, that has a wavelength of $700 nm$ ? The speed of light is always $300,000,000m/_s$ or $3\times10^8m/_s$ . The speed of a wave depends on the medium the wave is travelling through. We will look at this more closely in later lessons.