# Electronic Devices and Circuits Questions and Answers – The Hybrid PI CE Transistor Model

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Hybrid PI CE Transistor Model”.

1. What is the value of input resistance in the hybrid-pi CE transistor model?
a) hoe
b) hib
c) hic
d) hie

Explanation: The input resistance of a common emitter (CE) amplifier can be expressed in terms of hybrid parameters in the hybrid-pi CE transistor model. The input resistance is universally expressed as hie . This is also the same for approximate as well as exact hybrid models.

2. How do we calculate the value of IC in the hybrid-pi CE transistor model?
a) IC = hre × IB
b) IC = -hre × IB
c) IC = hfe × IB
d) IC = -hfe × IB

Explanation: The collector current of a common emitter (CE) amplifier can be expressed in terms of hybrid parameters in the hybrid-pi CE transistor model. It is expressed as the product of hfe × IB . This is the same for approximate hybrid models as well.

3. What is the value of current gain in the hybrid-pi CE transistor model?
a) hfe
b) -hfe
c) hre
d) –hre

Explanation:The current gain of a common emitter (CE) amplifier can be expressed in terms of hybrid parameters in the hybrid-pi CE transistor model. The current gain hfe is the forward transfer characteristics and is used to calculate the current gain in common emitter amplifiers.

4. What is the value of voltage gain in the hybrid-pi CE transistor model?
a) hfe × RL / hre
b) –hfe × RL / hre
c) hfe × RL / hie
d) –hfe × RL / hie

Explanation: The voltage gain of a common emitter (CE) amplifier can be expressed in terms of hybrid parameters in the hybrid-pi CE transistor model. The voltage gain is equal to -hfe × RL / hie where, RL is load resistance, hie is input resistance and -hfe is the current gain.

5. What is the magnitude of voltage generated at emitter circuit of a hybrid-pi CE transistor model?
a) hre × hfe / Ib × RL
b) hre × hfe × Ib × RL
c) hre × hfe / IC × RL
d) hre × hfe × IC × RL

Explanation: The magnitude of voltage generated at emitter circuit of a common emitter (CE) amplifier can be expressed in terms of hybrid parameters in the hybrid-pi CE transistor model. The magnitude of voltage generated is equal to hre × hfe × Ib × RL where, RL is load resistance and Ib is the base current.
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6. What is the value of output resistance in the hybrid-pi CE transistor model?
a) ∞
b) 0
c) hic
d) hie

Explanation: The output resistance in a simplified common emitter hybrid model is calculated as the ratio of collector voltage over collector current while VS is equal to zero and RL is omitted. Due to this configuration IC is equal to zero and hence output resistance is infinite.

7. What is the value power gain in the hybrid-pi CE transistor model?
a) AV – AI
b) AV + AI
c) AV × AI
d) AV / AI

Explanation: The power gain in a simplified common emitter hybrid model is calculated as the product of voltage gain and power gain. It is expressed as AV × AI . It can also be further simplified as AI2 × RL / Ri , where RL is load resistance and Ri is input resistance.

8. What is the value of overall current gain in the hybrid-pi CE transistor model while considering RS ?
a) AI × IB / IS
b) AI × IC / IS
c) AI × IS / IC
d) AI × IS / IB

Explanation: The current gain in a simplified common emitter hybrid model while considering RS is calculated as the product of current gain without external parameters and the ratio of base current and external applied current. It is expressed as AI × IB / IS . Where, IS is the external applied current on the amplifier.

9. What is the value of overall voltage gain in the hybrid-pi CE transistor model while considering RS ?
a) VB / VS
b) VC / VS
c) VB × VS
d) VC × VS

Explanation: The overall voltage gain in a simplified common emitter hybrid model while considering RS is calculated as ratio of base voltage over the applied external voltage. It is expressed as VB / VS . Where, VS is the external applied voltage on the amplifier.

10. We use hybrid-pi CE transistor model to obtain approximate values.
a) True
b) False

Explanation: It is more practical to calculate the approximate values of voltage and current gains instead of computing the exact values of a common emitter amplifier circuit. We use a simplified common emitter hybrid model to obtain these approximate values without reducing the accuracy.

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