Electronic Devices and Circuits Questions & Answers - Page 7

31.

In a bipolar transistor, the barrier potential is

A.

0

B.

a total of 0.7 V

C.

0.7 V across each depletion layer

D.

0.35 V

Correct answer is C

Since there are two p-n junctions, there are two depletion layers and 0.7 V across each layer.

32.

A silicon (PN) junction at a temperature of 20°C has a reverse saturation current of 10 pico Ampere. The reverse saturation current at 40°C for the same bias is approximately.

A.

30 pA

B.

40 pA

C.

50 pA

D.

60 pA

Correct answer is B

By increasing the temperature by 10°C, Io becomes double. So by increasing temperature by 20°C, Io becomes 4 times the initial value... and it is 40 PA.

33.

A transistor has two p-n junctions. The batteries should be connected such that

A.

both junctions are forward biased

B.

both junctions are reverse biased

C.

one junction is forward biased and the other is reverse biased

D.

none of the above

Correct answer is C

Emitter-base junction is forward biased and base collector junction is reverse biased.

34.

The number of doped regions in PIN diode is

A.

1

B.

2

C.

3

D.

1 or 2

Correct answer is B

A PIN diode has p and n doped regions separated by intrinsic layer.

35.

An LED has a rating of 2 V and 10 mA. It is used along with 6V battery. The range of series resistance is

A.

0 to 200 Ω

B.

200 - 400 Ω

C.

200 Ω and above

D.

400 Ω and above

Correct answer is D

R = (6-2/10x10-3) = 400Ω.

R must be at least 400Ω so that current in LED does not exceed 10 mA.