Basic Electronics Laboratory Viva Questions 1

1. The efficiency of an LED for generating light is directly proportional to the

1. Temperature
2. Voltage applied
3. Level of doping
4. Current injected

Answer: [D] Current injected

2. A Semiconductor photodiode uses

1. Photoemissive effect
2. Photovoltaic effect
3. Photoconductive effect
4. None of the above

Answer: [C] Photoconductive effect

3. LED gives off visible light from

1. Both P and N regions
2. P region alone
3. N region alone
4. Region of depletion Layer

Answer: [D] Region of depletion Layer

4. The colour of the light emitted by a LED depends on

1. Its forward bias
2. Its reverse bias
3. The amount of forward current
4. The type of semiconductor material used.

Answer: [D] The type of semiconductor material used.

5. In a forward biased photo diode with increase in incident light intensity the diode current

1. Increases
2. Remains constant
3. Decreases
4. Remaining constant,the voltage drop across the diode increases.

Answer: [C] Decreases

6. The BJT transistor is

1. Voltage controlled device
2. Current controlled device
3. Both A and B
4. None of the above

Answer: [B] Current controlled device

7. In a PNP transistor with VEB set to 0 and VCB reverse bias ( P negative w.r.t to N region) there is a current flow. The following four statements refer to this current

1. The current is due to diffusion.
2. It is dependent on VCB
3. It is due to drift in the electric field
4. It is due to thermally generated minority carriers

Of these the true statements are

1. Only 1,2
2. Only 2,3
3. Only 3,4
4. Only 1,4

Answer: [C] Only 3,4

8. The base width in a junction transistor is deliberately chosen small so that

1. The electric field is large
2. The concentration gradient of injected carriers is small
3. To reduce recombination of injected minority carriers
4. The majority carriers easily reach the collector

Answer: [C] To reduce recombination of injected minority carriers

9.In a PNP transistor biased to operate in the active region,the current in the base region consists of

1. Only holes
2. Only electrons
3. Predominantly holes
4. Predominantly electrons

Answer: [C]

10. The (1) region of the transistor is more heavily doped than (2) and (3) regions.

1. Emitter,collector,base
2. Collector,emitter,base
3. Base,collector,emitter
4. Base,emitter,collector

Answer: [A] Emitter,collector,base