Page 1022 - Basic Electrical Engineering

58. Give one practical application of a phototransistor.
59. Write short explanations of the following:

(i) phototransistor; (ii) photo-darlington; (iii) optocoupler, and (iv) solar cell.
60. Explain the formation of the depletion region in an unbiased p–n junction.
61. What are the barrier potentials of silicon diodes and germanium diodes?
62. Explain how a depletion-type MOSFET can work either in an enhancement mode or in a
depletion mode.
63. Name two major differences between a JFET and a MOSFET.

B. Multiple Choice Questions

1. Which of the following is a semiconductor material?

a. Ceramic
b. Silicon
c. Cadmium
d. Rhodium.

2. Which of the following statements is correct?

a. Germanium valence electrons will need a smaller amount of additional energy to
escape from the atom than silicon valence electrons
b. Valence electrons of silicon are in the fourth shell while those of germanium are in
the third shell
c. Silicon is more widely used semiconductor material than germanium
d. Germanium produces less number of electron hole pairs than silicon.

3. Which of the following is not shown in the energy band diagram?

a. Permeable energy band
b. Conduction band
c. Valence band
d. Forbidden gap.

4. Which of the following statements is not true?

a. Semiconductors have negative temperature coefficient of resistance
b. Insulators have positive temperature coefficient of resistance
c. Insulators have negative temperature coefficient of resistance
d. Conductors have positive temperature coefficient of resistance.

5. Which of the following statements is not true?

a. In both silicon and germanium atoms there are four valence electrons
b. Intrinsic semiconductors behave like conductors at low temperatures
c. Intrinsic semiconductors behave like insulators at low temperatures