CBT Electronic & Electrical Fundamentals 3 — Questions and Answers
Question 1: In a common-emitter BJT amplifier, what is the phase relationship between input and output signals?
- In phase (0°)
- 90° phase shift
- 180° phase shift (Correct answer)
- 270° phase shift
Correct answer: 180° phase shift
A common-emitter amplifier inverts the signal, producing a 180° phase shift between input and output.
Question 2: What is the time constant of a circuit with a 10kΩ resistor and a 100μF capacitor?
- 0.1 seconds
- 1 second (Correct answer)
- 10 seconds
- 0.01 seconds
Correct answer: 1 second
The RC time constant τ = R × C = 10,000Ω × 0.0001F = 1 second.
Question 3: What does the term 'dBm' represent in RF and broadcast engineering?
- Decibels relative to 1 milliwatt (Correct answer)
- Decibels relative to 1 millivolt
- Decibels of modulation
- Decibels per meter
Correct answer: Decibels relative to 1 milliwatt
dBm is a unit of power expressed in decibels relative to a reference of 1 milliwatt.
Question 4: In a full-wave rectifier with a center-tapped transformer, how many diodes are required?
- One
- Two (Correct answer)
- Three
- Four
Correct answer: Two
A center-tapped full-wave rectifier uses two diodes, one for each half of the AC cycle from the center-tapped secondary.
Question 5: What is the voltage gain of an op-amp inverting amplifier with a feedback resistor of 100kΩ and an input resistor of 10kΩ?
- +10
- -10 (Correct answer)
- +0.1
- -0.1
Correct answer: -10
The gain of an inverting op-amp amplifier is -Rf/Rin = -100kΩ/10kΩ = -10.
Question 6: Which type of capacitor is commonly used in high-frequency RF circuits due to its low parasitic inductance?
- Electrolytic capacitor
- Tantalum capacitor
- Surface-mount ceramic chip capacitor (Correct answer)
- Mylar film capacitor
Correct answer: Surface-mount ceramic chip capacitor
Surface-mount ceramic chip capacitors have extremely low parasitic inductance and are ideal for high-frequency RF bypass and decoupling applications.
Question 7: What is the Q factor of an inductor primarily a measure of?
- The inductor's maximum current rating
- The ratio of energy stored to energy dissipated per cycle (Correct answer)
- The inductor's resonant frequency
- The number of turns in the winding
Correct answer: The ratio of energy stored to energy dissipated per cycle
Q factor (quality factor) measures the ratio of reactive power stored to real power dissipated, indicating how 'ideal' the inductor is.
CBT Electronic & Electrical Fundamentals 3
In a common-emitter BJT amplifier, what is the phase relationship between input and output signals?