An electromagnetic wave in a vacuum has a wavelength of 0.07 m. What is its

frequency?

4.3 x 108 m/s

4.3 x 10' Hz

3.0 x 108 m/s

3.0 x 10' Hz

Answer is B (assuming it's meant to say 4.3 x 10^10 Hz)

Explanation:

Right away you can eliminate A and C because the units are wrong - m/s is units of speed, not frequency (whose units are Hz).

In general the product of an electromagnetic wave's wavelength (λ) and frequency (f) in a vacuum is equal to the speed of light (c):

λf = c

Knowing that c = 3 x 10^8 and λ = 0.07 you get:

0.07f = 3 x 10^8

f = 3 x 10^8 / 0.07

f = 4.3 x 10^10