Assume the amplitude of the electric field in a plane electromagnetic wave is E1
ID: 1352327 • Letter: A
Question
Assume the amplitude of the electric field in a plane electromagnetic wave is E1 and the amplitude of the magnetic field is B1. The source of the wave is then adjusted so that the amplitude of the electric field doubles to become 2E1.
(i) What happens to the amplitude of the magnetic field in this process?
It becomes four times larger.
It becomes two times larger.
It can stay constant.
It becomes one-half as large.
It becomes one-fourth as large.
(ii) What happens to the intensity of the wave?
It becomes four times larger.
It becomes two times larger.
It can stay constant.
It becomes one-half as large.
It becomes one-fourth as large.
Explanation / Answer
(1) It becomes two times larger.
Because the amplitudes are always directly proportional.
(2) It becomes four times larger.
Because the intensity of any wave is always proportional to the square of its amplitude.
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