UPSC Recruitment Paper 2019 : Joint Assistant Director, Directorate of Coordination Police Wireless

1.Suppose a specimen (metal or semiconductor) carrying a current I is placed in a transverse magnetic field B, an electric field ε is induced in the direction perpendicular to both I and B. Then this phenomenon is known as
(a) Mobility
(b) Super conductivity
(c) Hall effect
(d) Diffusion

2. The rate of change of collector current with respect to the reverse saturation current, keeping β and VBE constant, is called
(a) Stability factor
(b) Fixed bias
(c) Load line
(d) Bias compensation

3. Which one of the following has negative temperature coefficient?
(a) Sensistor
(b) Thermistor
(c) Metal
(d) Heavily doped semiconductor

4. If a conductor of length L, carrying a current of I, is placed in a magnetic field of intensity B, then the force fm acting on this conductor is (assuming that the directions of I and B are perpendicular to each other)
(a) fm = BIL
(b) fm = BI/L
(c) fm = LI/B
(d) fm = 2BI/L

5. In a P-N junction diode, if a forward-bias potential (Vd) is zero, then
(a) The forward-bias current (Id) will be equal to the reverse saturation current (Is)
(b) The forward-bias current (Id) will be equal to the negative of reverse saturation
current (Is)
(c) Id will be zero
(d) Id = 2Is

6. What is the cutoff frequency of the op-amp, if unity gain frequency is 10 MHz and voltage differential gain is 50,000?
(a) 200 Hz
(b) 100 Hz
(c) 1000 Hz
(d) 2000 Hz

7.Which of the following elements are most frequently used for formation of p-type material by doping a pure germanium or silicon crystal with impurity atoms having three valence electrons?
(a) Antimony, Arsenic, Boron
(b) Boron, Gallium, Arsenic
(c) Phosphorus, Boron, Gallium
(d) Boron, Gallium, Indium

8. Consider the following statements for sampling:
1. Flat-top sampling is preferred because of its noise immunity.
2. In natural sampling, the top of each rectangular pulse remains constant and is equal to the instantaneous value of the signal x(t) at the start of sampling.
3. One important reason for intentionally lengthening the duration of each pulse in flattop sampling is to reduce the bandwidth.
Which of the above statements are correct?
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3