Everything Science Grade 12

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.