DRDO 2009 solved answers Part-1

The students appeared in DRDO (Defence Research and Development Organisation) SET-2009 ( 6th september) can get some of the answers here for verification. Please let me know your comments.

1. At room temperature, which one of the following band gap energy corresponds to that of a semiconductor?

a. Eg = 0ev b. Eg = 1.2ev c. Eg = 5ev d. Eg = 9ev

Ans: 1.2ev

2. The diffusion constant and mobility for electrons in a semiconductor material at a given temperature are 20 cm2/s and 1600 cm2/V-s, respectively. The thermal voltage VT for a diode made of this material at the same temperature is

a. 125mv b. 32mv c.12.5mv d. 3.2mv

Ans: Given: diffusion constant = 20 cm2/s and mobility for electrons=1600 cm2/V-s

we know that, diffusion constant/mobility for electrons=VT

So 12.5mv is the answer

3. If Cd and Cs represent the depletion and diffusion capacitances of a diode respectively, which one of the following statements is NOT correct?

a. Cd varies inversely with the depletion width.

b. Cs varied directly with the rate of change of diode current with respect to diode voltage.

c. Cd varies directly with the Transit time.

d. Effective junction capacitance is the parallel combination of Cd and Cs.

Ans: c

4. The correct match between the following two columns is

P. Tunnel diode i. Microwave amplification

Q. Zener diode ii. Voltage Regulation

R. PIN diode iii. Photo detection

S. Schottky diode iv. High Speed switching

a. P-iii;Q-iv;R-ii;S-I b. P-i;Q-iii;R-ii;S-iv c. P-iv;Q-ii;R-i;S-iii d. P-i;Q-ii,R-iii;S-iv

Ans: d

5. The I-V characteristics of devices can be divided into quadrants as shown in fig below

Photo diodes and solar cells are normally operated in quadrants

a. Q3 and Q4, respectively b.Q1 and Q1, respectively c.Q1 and Q3, respectively

d. Q2 and Q3, respectively

Ans: a

6. Adding a degeneration resistor Re to a CE BJT amplifier will mainly reduce

a. the voltage gain

b. the input impedance

c. the amplifier bandwidth

d. the output impedance

Ans: a

7. A BJT Darlington pair has

a. high input impedance and high beta

b. high input impedance and low beta

c. low input impedance and high beta

d. low input impedance and low beta

Ans: a

8. In the logic equation A(A+B’C’+C)+B’(C’+A’+BC)(A+B’C+AC’)=1. If C=A’ then

a. A+B=1 b. A’+B=1 c. A+B’=1 d. A=1

Ans: c

9. A gate having two inputs (A,B) and one output (Y) is implemented using 4:1 mux as shown below. A1(MSB) and A0 are the control bits and I0 – I3 are the inputs to the Mux. The gate is:

a. NAND b. NOR c. XOR d. OR

Ans: d

10. A 4-bit serial in parallel out shift register is used with a feedback as shown below. The shifting sequence is Qa->Qb->Qc->Qd

If the output is 0000 initially, the output repeats after

a. 4 clock pulses b. 6 clock pulses c. 15 clock pulses d. 16 clock pulses

Ans: b

11. In a super heterodyne receiver, if the intermediate frequency is 10.7MHz and the carrier frequency is 89.6MHz, the image frequency is

a. 78.9MHz b. 100.3MHz c. 111MHz d. 121MHz

Ans: 111Mhz Image frequency = 2IF+Carrier Frequency

The remaining question solution will be given after 2days.