Transistor as Amplifier CE Configuration - UNSOLVED PRACTICE SET
Chapter: Semiconductor Electronics | Topic: Transistor as Amplifier CE Configuration
TRANSISTOR AS AMPLIFIER CE CONFIGURATION - UNSOLVED PRACTICE SET
Topic: Transistor as Amplifier CE Configuration
Multiple Choice Questions
Q1. In a common-emitter amplifier, the input is applied between:
- Collector and emitter
- Base and emitter
- Collector and base
- Any two terminals
Q2. The voltage gain of a common-emitter amplifier is given by:
- A_V = β × (R_C / R_in)
- A_V = −β × (R_C / r_e)
- A_V = α × (R_C / R_E)
- A_V = R_C / R_E
Q3. The negative sign in the voltage gain expression of a CE amplifier indicates:
- Power loss
- A 180° phase shift between input and output
- Negative feedback
- Reduced gain
Q4. The current gain β of a CE amplifier is defined as:
- ΔI_C / ΔI_E
- ΔI_C / ΔI_B
- ΔI_E / ΔI_B
- ΔI_B / ΔI_C
Q5. The input impedance of a CE amplifier is:
- Very high
- Moderate (typically 1-2 kΩ)
- Moderate (typically 1-2 kΩ)
- Equal to the load resistance
Q6. The output impedance of a CE amplifier is:
- Very low
- Moderate to high (typically equal to R_C)
- Very high
- Equal to the input impedance
Short Answer Questions
Q7. Draw the circuit diagram of a common-emitter amplifier and label all components.
Q8. Why is the common-emitter configuration the most widely used transistor amplifier configuration?
Q9. Explain why there is a 180° phase shift between the input and output voltages in a CE amplifier.
Q10. What is the role of the coupling capacitors in a CE amplifier circuit?
Q11. Why is the Q-point (quiescent point) important in a transistor amplifier? What happens if the Q-point is not properly set?
Q12. Draw the input and output waveforms of a CE amplifier showing the phase relationship.
Long Answer Questions
Q13. Explain the working of a common-emitter amplifier with a circuit diagram. Derive the expression for voltage gain and explain why there is a phase reversal between input and output.
Q14. Describe how the transistor is biased in a CE amplifier to operate in the active region. Explain the concept of the Q-point and discuss how it affects the faithful amplification of the input signal.
Q15. Discuss the frequency response of a CE amplifier. What factors limit the gain at low and high frequencies? Draw a typical frequency response curve.
Numerical & Application-based Problems
Q16. A CE amplifier has the following parameters: R_C = 2 kΩ, R_E = 500 Ω, β = 100, V_CC = 12 V. The input signal has a peak value of 10 mV.
(a) Calculate the AC emitter resistance r_e (assume thermal voltage V_T = 26 mV and I_E ≈ 1 mA).
(b) Calculate the voltage gain of the amplifier.
(c) Calculate the peak output voltage.
(d) Calculate the current gain and power gain.
Q17. A transistor amplifier circuit has V_CC = 15 V, R_C = 3 kΩ, R_B = 300 kΩ, and β = 100.
(a) Calculate the base current I_B.
(b) Calculate the collector current I_C.
(c) Calculate the collector-emitter voltage V_CE.
(d) Determine whether the transistor is in the active region.
(e) Calculate the voltage gain if a load R_L = 3 kΩ is connected.
Q18. In your school electronics club, students are building a simple audio amplifier.
(a) A student uses a CE amplifier with R_C = 1 kΩ and wants a voltage gain of −50. If the transistor has β = 100, calculate the required emitter current and the AC emitter resistance.
(b) The student connects a microphone that produces 5 mV peak signal. Calculate the expected output voltage and explain why this is suitable for driving a small speaker.
(c) She then adds an emitter bypass capacitor across R_E. Explain how this increases the voltage gain and what trade-off it introduces.
(d) A classmate builds the same circuit but forgets the coupling capacitor at the input. Explain what happens to the DC bias when the microphone is connected directly, and why the capacitor is essential.
(e) In India, audio amplifiers are used in public address systems at schools, temples, and events. Explain why CE amplifiers are preferred for the initial stages of these systems and what additional circuits (like power amplifiers) are needed for the final output.