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Question

A 27 mW laser beam has a cross-sectional area of 10 mm2. The magnitude of the maximum electric field in this EM wave is given by [Given permittivity of space ε0=9×1012 F/m, speed of light c=3×108 m/s]

A
2 kV/m
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B
1 kV/m
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C
0.7 kV/m
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D
1.4 kV/m
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Solution

The correct option is D 1.4 kV/m
Given:
P=27 mW, A=10 mm2

ε0=9×1012 F/m, c=3×108 m/s

The intensity of the electromagnetic wave is given by,

I=PA=12ε0E2c

E=2PAEc

Substituting the values,

E=2×27×10310×106×9×1012×3×108

E=2×106=1.4×103 V/m

E=1.4 kV/m

Hence, option (D) is correct correct answer.

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