Which statement about electromagnetic radiation is correct?

 Question 26

Which statement about electromagnetic radiation is correct?

A Waves of wavelength 5 × 10^-9 m are high-energy gamma rays.

B Waves of wavelength 3 × 10^-8 m are ultra-violet waves.

C Waves of wavelength 5 × 10^-7 m are infra-red waves.

D Waves of wavelength 9 × 10^-7 m are light waves.

 

 

 

Reference: Past Exam Paper – November 2014 Paper 11 & 12 Q22

 

 

 

Solution:

Answer: B.

Estimates for the different components of the electromagnetic spectrum should be known at A-Level.

 

All EM waves travel at the same speed of 3.0×10⁸ m s^-1.

Gamma rays have the highest frequencies, followed by X-rays and UV.

 

v = fλ

 

For the given wavelength of UV waves,

f = v / λ = 3.0×10⁸ / 3.0×10^-8 = 1×10¹⁶ Hz

 

This is a correct estimate for the frequency of UV waves.