# Electronic Devices and Circuits Questions and Answers – The CE Short Circuit Gain Obtained with the Hybrid PI Model

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The CE Short Circuit Gain Obtained with the Hybrid PI Model”.

1. Why do we need CE short circuit gain obtained with hybrid pi model?
a) To provide a non – linear output
b) To maintain transistor in active region
c) To maintain transistor in saturation region
d) To maintain transistor in cut – off region

Explanation: We use a CE short circuit gain obtained with hybrid pi model to collect negative feedback and to maintain the transistor in an active region. To maintain stability in active region, the DC base biased voltage is resultant from the collector voltage VC .

2. What is the function of RE in the CE short circuit gain obtained with hybrid pi model?
a) To improve stability and decrease positive feedback
b) To improve stability and increase positive feedback
c) To improve stability and decrease negative feedback
d) To improve stability and increase negative feedback

Explanation: In a CE short circuit gain obtained with hybrid pi model circuit, the emitter resistor provides additional stability along with increasing the negative feedback sent to the collector. The addition of the emitter resistance enables the transistor’s emitter to no longer be grounded to zero – volt potential.

3. In the circuit given below, assume VCC = 5V, VBE = 0.7V, RE = 10kΩ, RB = 20kΩ and β = 50. How much is the current IE ?

a) 0.561mA
b) 0.335mA
c) 0.413mA
d) 0.513mA

Explanation: To find the value of IE, we substitute the values in the below equation. Given values are VCC = 5V, VBE = 0.7V, RE = 10kΩ, RB = 20kΩ and β = 50.
IE = (VCC – VBE) / (RE + (RB / β))
IE = (5 – 0.7) / (10 + (20 / 50))
IE = 4.3 / (10 + 0.4) = 0.413mA.

4. What happens if collector current increases in a CE short circuit gain obtained with hybrid pi model?
a) Emitter voltage increases therefore base voltage increases
b) Emitter voltage decreases therefore base voltage decreases
c) Emitter voltage increases therefore base voltage decreases
d) Emitter voltage decreases therefore base voltage increases

Explanation: If the collector current IC is increased, the corresponding emitter current also increases. Which in turn causes the voltage across RE to increase. This in turn causes a proportional rise in the base voltage since VB = VE + VBE .

5. Why is CE short circuit gain obtained with hybrid pi model better for linear circuits?
a) Independent of β
b) Dependent on β
c) Highly predictable
d) Not stable

Explanation: CE short circuit gain obtained with hybrid pi model is better for linear circuits as compared to self – bias circuits as it is dependent on β. Voltage divider bias circuits are highly predictable whereas self – bias circuits are independent of β. Therefore, for a CE short circuit gain obtained with hybrid pi model linear circuits are preferred.
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6. How does emitter resistor RE provide stability in CE short circuit gain obtained with hybrid pi model?
a) Consumes less power
b) Has an easier circuit design
c) Automatically biases the circuit
d) It does not provide stability

Explanation: In a CE short circuit gain obtained with hybrid pi model, the emitter resistor provides stability by automatically biasing the circuit using negative feedback. The negative feedback negates any change due to the collector current with an opposing change provided by the base bias voltage and thus helps maintain circuit stability.

7. In the circuit given below, assume VCC = 12V, VBE = 0.7V, RB = 330kΩ, RC = 3.3kΩ, RE = 2.7kΩ and β = 50. What is the base current IB?

a) 16.432µA
b) 17.856µA
c) 20.542µA
d) 17.936µA

Explanation: To find the value of IB, we substitute the values in the below equation. Given values are VCC = 12V, VBE = 0.7V, RB = 330kΩ, RC = 3.3kΩ, RE = 2.7kΩ and β = 50.
IB = (VCC – VBE) / (RB + β × (RC + RE))
IB = (12 – 0.7 / (330 + 50 × (2.7 + 3.3)) = 11.3 / (330 + 50 × 6) = 11.3 / 630 = 17.936µA.

8. How do you calculate the value of VCE in CE short circuit gain obtained with hybrid pi model?
a) VCE = VCC + IC (RC + RE)
b) VCE = VCC – IC (RC + RE)
c) VCE = VCC – IC (RB + RE)
d) VCE = VCC + IC (RB + RE)

Explanation: The value of VCE can be calculated using this equation: VCE = VCC – IC (RC + RE). It is the voltage between the collector and emitter terminal of the transistor and is measured as the output of the transistor.

9. How does the negative feedback help a CE short circuit gain obtained with hybrid pi model circuit?
a) Helps make it more predictable
b) Provides opposing change in base voltage
c) Helps make it more predictable, provides opposing change in base voltage
d) It doesn’t affect

Explanation: The negative feedback in a CE short circuit gain obtained with hybrid pi model circuit provides a negative feedback which in turn helps make the circuit more predictable as it provides opposing change in the base voltage which cancels out any change in the collector current.

10. What are the disadvantages of CE short circuit gain obtained with hybrid pi model circuits?
a) Requires few resistors
b) Provides a lot of stability
c) Provides negative feedback
d) Provides positive feedback

Explanation: A collector emitter bias circuit provides negative feedback as well as requires multiples resistors for a small change. The negative feedback limits the frequency range it will work in. Higher frequencies will provide poor performance. It also requires a greater number of resistors just to provide a stability against a small parameter.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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