Question 3
Electromagnetic waves
of wavelength λ and frequency f travel
at speed c in a vacuum.
What describes the
wavelength and speed of electromagnetic waves of frequency f /
2?
Wavelength Speed in a vacuum
A λ / 2 c / 2
B λ / 2 c
C 2λ c
D 2λ 2c
Reference: Past Exam Paper – June 2013 Paper 13 Q24
Solution:
Answer:
C.
The speed of EM waves in
vacuum is c.
Speed c = f λ
Wavelength λ = c / f
The speed of all EM waves
in vacuum is constant (= c).
If the frequency is now
f/2
Speed in vacuum = c
New wavelength = c / (f/2)
= 2c / f
Since λ = c / f,
New wavelength = 2 λ
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