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.
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