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):

• if the wavelength increases -> the frequency will decrease
• if the wavelength decreases -> the frequency will increase

Similarly:

• if the frequency increases -> the wavelength will decrease
• if the frequency decreases -> the wavelength will increase

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

What changes: frequency or wavelength?

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

The frequency doesn’t change.