Discussion :: Exam Questions Paper
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Assertion (A): Conductors do not permit propagation of waves more than a short distance into the conductor at microwave frequencies.
Reason (R): The relaxation time constant for conductors is much small than the period of centimetric EM wave.
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A.
Both (A) and (R) are true and (R) is the correct explanation of (A)
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B.
Both (A) and (R) are true but (R) is not the correct explanation of (A)
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C.
(A) is true but (R) is false
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D.
(A) is false but (R) is true
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Answer : Option B
Explanation :
Depth of penetration = 
, where 
= relaxation time.
δ would be small, if σ is large, which itself depends upon relaxation time.
t for conductors is of the order of 10-14 s, for λ = 3 x 10-2 cm
∴ period of centimetric EM waves
= 
Therefore, even though t is much smaller than period of centimetric waves but it is not the correct reason for the assertion given.
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