Question

A certain part of the electromagnetic spectrum ranges from 200 nm to 400 nm. what is the lowest frequency associated with this portion of the spectrum? (c 3.00 108 m/s)

Answer 1

The lowest and highest wavelengths of this part of the electromagnetic spectrum are:
$\lambda_1 = 200 nm=200 \cdot 10^{-9} m$
$\lambda_2 = 400 nm = 400 \cdot 10^{-9} m$

We can calculate the corresponding frequencies by using:
$f= \frac{c}{\lambda}$
where c is the speed of light. If we use this equation, we find:
$f_1 = \frac{c}{\lambda_1}= \frac{3 \cdot 10^8 m/s}{200 \cdot 10^9 m} =1.5 \cdot 10^{15}Hz$
$f_2 = \frac{c}{\lambda_2}= \frac{3 \cdot 10^8 m/s}{400 \cdot 10^9 m} =7.5 \cdot 10^{14}Hz$
Therefore, the lowest frequency associated with this portion of the spectrum is 
$f_2 = 7.5 \cdot 10^{14} Hz$