Question

which is the correct formula for finding the frequency of an electromagnetic wave?
$f = c - \lambda$
$f = \frac{\lambda}{c}$
$f = \lambda + c$
$f = \frac{c}{\lambda}$

Explanation:

Step1: Recall the wave - speed formula

The speed of a wave \( v = f\lambda \), where \( v \) is the speed of the wave, \( f \) is the frequency, and \( \lambda \) is the wavelength.

Step2: For electromagnetic waves

The speed of electromagnetic waves in vacuum \( c = f\lambda \) (where \( c\approx3\times 10^{8}\ m/s\)).

Step3: Solve for frequency \( f \)

From \( c = f\lambda \), we can rearrange the formula to get \( f=\frac{c}{\lambda} \).

Answer:

\( f=\frac{c}{\lambda} \) (the fourth option)