# What is an example of an electromagnetic radiation practice problem?

Apr 25, 2015

Background: Electromagnetic radiation moves at the speed of light in a vacuum. The speed of light, $c$, to three significant figures, is $3.00 \times {10}^{8} \text{m/s}$. The relationship between wavelength, $\lambda$, and frequency, $f$, is $c = \lambda \cdot f$.

Question: If the wavelength of a photon of red light is $725 \text{nm}$, what is its frequency?

Convert $725 \text{nm}$ to meters. ($1 \text{m"=1xx10^9"nm}$)
$725 \cancel{\text{nm"xx(1 "m")/(1xx10^9 cancel"nm")=7.25xx10^(-7) "m}}$
Rearrange $c = \lambda \cdot f$ to solve for $f$.
f=c/lambda = (3.00xx10^8 cancel("m")/s")/(7.25xx10^(-7) cancel(m)= $4.14 \times {10}^{14} \text{/s"=4.14xx10^14 "Hz}$