15.4 CHAPTER 15. EM RADIATION
Example 1: EM spectrum I
QUESTION
Calculate the frequencyof red light with a wavelength of 4 , 2 × 10 −^7 m
SOLUTION
We use the formula: c = fλ to calculate frequency.The speed of light is a
constant 3 × 108 m/s.
c = fλ
3 × 108 = f× 4 , 2 × 10 −^7
f = 7, 14 × 1014 Hz
Example 2: EM spectrum II
QUESTION
Ultraviolet radiation hasa wavelength of 200 nm. What is the frequencyof the
radiation?
SOLUTION
Step 1 : To calculate the frequency we need to identify the wavelength
and the velocity of theradiation.
Recall that all radiation travels at the speed of light (c) in vacuum.
Since the question doesnot specify through what type of material
the Ultraviolet radiationis travelling, one can assume that it is
travelling through a vacuum. We can identifytwo properties of
the radiation - wavelength (200 nm) and speed (c).
Step 2 : We can use the equation c = fλ to find the frequency since the
wavelength is given.