If a runner runs 400 metres in 80 seconds, how would you calculate how fast he was going?


Remember the unit for frequency is Hertz$(Hz)$ which is equal to $^1/_s$ .


Wavelength is a measure of **distance.**



Think about the equation for speed, $speed = \frac{distance}{time}$ . Replace the values with their units.


This would be seconds / metres, or time/distance. Try again!

The equation for frequency is $f=\frac{1}{T}$ . The unit for time period is second so the unit for frequency is $\frac{1}{s}=^1/_s$ , or 'per second'.


Wavelength is a measure of distance, so the SI unit is metres $(m)$ .


If you replace the units in $m \times \frac{1}{s}$ with wavelength and frequency, you get that $speed = wavelength \times frequency$, so **B** is the correct answer. 


Create an equation with the units and then replace them with their values!


If you substitute in the units this would give you$\frac{metres}{\frac{1}{seconds}}=metres \times seconds$ or $ms$.  This is not the unit for speed!


$v=f\times\lambda$

Rearrange $v=\lambda\times f$ to make $\lambda$ the subject.


To rearrange the equation to make f the subject, $v=\lambda\times f$ you must divide both sides by$f$ not, $\lambda$.

Rearrange $v=\lambda\times f$ to make $f$ the subject.Remember to always convert units into their respective **SI units** before performing calculations.

Multiplying speed and wavelength together does not give you frequency. To rearrange the equation $v=\lambda\times f$ to make $f$ the subject, you must divide both sides by $\lambda$ .

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

Speed of Wave

Waves of Information

Transverse and Longitudinal Waves

Amplitude and Wavelength

Wavefront

Period and Frequency

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