Speed of electromagnetic wave

The speed of any electromagnetic (or EM) wave is around 3.00\times10^8ms^{-1} in a vacuum.

Wavelength and frequency changes

Because of our equation linking wavelength (\lambda), frequency (f) and velocity (v):

v=f\lambda

We can re-arrange it to find the frequency, f:

f=\frac v{\lambda}

Or, to find the wavelength, \lambda:

\lambda=\frac vf

From this, we can tell that (if velocity remains constant):

Similarly:

Again, this only works if velocity remains constant. With an EM wave, the velocity is always constant for any type of electromagnetic wave!

If The speed of an EM wave changes, then the [[wavelength]] changes.

The frequency doesn’t change.

Question	Answer
What is the speed of an electromagnetic wave in a vacuum?	3.00 \times 10^8 \text{ ms}^{-1}
What equation links wavelength (\lambda), frequency (f), and velocity (v) of a wave?	v = f \lambda
How do you rearrange v = f \lambda to find frequency?	f = \frac{v}{\lambda}
How do you rearrange v = f \lambda to find wavelength?	\lambda = \frac{v}{f}
If the velocity of an EM wave is constant and the wavelength increases, what happens to frequency?	The frequency decreases.
If the velocity is constant and the wavelength decreases, what happens to frequency?	The frequency increases.
If the frequency of an EM wave increases while velocity is constant, what happens to wavelength?	The wavelength decreases.
If the frequency of an EM wave decreases while velocity is constant, what happens to wavelength?	The wavelength increases.
If the speed of an EM wave changes, which property (wavelength or frequency) changes?	Wavelength.
If the speed of an EM wave changes, which property (wavelength or frequency) stays constant?	The frequency does not change.