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Exam Questions Papers - Engineering

Q1:

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.

A Both (A) and (R) are true and (R) is the correct explanation of (A)

B Both (A) and (R) are true but (R) is not the correct explanation of (A)

C (A) is true but (R) is false

D (A) is false but (R) is true

ANS:B - Both (A) and (R) are true but (R) is not the correct explanation of (A)

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.