CSIR Physical Sciences: Questions 251 - 252 of 401

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Question number: 251

» Electronics and Experimental Methods » Device Structure

Appeared in Year: 2013

MCQ▾

Question

A sample of Si has electron and hole motilities of 0.13 and 0.05m2Vs respectively at 300K . It is doped with P and Al with doping densities of 1.5×1021m3 and 2.5×1021m3 respectively. The conductivity of the doped Si sample at 300 K is – (Dec– 2013)

Choices

Choice (4) Response

a.

20.8Ω1m1

b.

8Ω1m1

c.

32Ω1m1

d.

51.20Ω1m1

Question number: 252

» Electronics and Experimental Methods » Filtering and Noise Reduction

Appeared in Year: 2013

MCQ▾

Question

The input to a lock – in amplifier has the from Vi(t)=Visin(ωt+θi) where Vi,ω,θi are the amplitude, frequency and phase of the input signal respectively. This signal is multiplied by a reference signal of the same frequency ω , amplitude Vr and phase θr . If the multiplied signal is fed to a low pass filter of cut – off frequency ω , then the final output signal is –

(June)

Choices

Choice (4) Response

a.

ViVr[cos(θiθr)cos(12ωt+θ1+θr)]

b.

ViVr[cos(θiθr)+cos(12ωt+θi+θr)]

c.

ViVrsin(θiθr)

d.

12ViVrcos(θiθr)

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