Free Electronics and Devices MCQs with Answers

• A. Cooling of the circuit
• B. Impedance matching
• C. Distortionless output
• D. Good frequency response

Explanation: A transformer reflects the load impedance according to the square of its turns ratio, allowing a speaker or other load to appear at the…

• A. Biasing the circuit
• B. Collector efficiency
• C. To keep the transformer cool
• D. None of the above

Explanation: Power amplifiers handle large currents and voltages, so efficient conversion of d.c. supply power into useful a.c.

• A. 5 kO
• B. 20 kO
• C. 100 kO
• D. 10 kO

Explanation: The primary-referred load is Zp = (Np/Ns)^2 Zs. With a 10:1 ratio and a 100-ohm secondary load, Zp = 10^2 × 100 = 10,000 ohms, or 10 kΩ.

• A. Either power or voltage
• B. Only power
• C. Only voltage
• D. None of the above

Explanation: Transformer coupling is useful wherever impedance transformation is needed, including both voltage amplifiers and power amplifiers.

• A. Keep the amplifier cool
• B. Protect from rusting
• C. Prevent induction due to stray magnetic fields
• D. None of the above

Explanation: Low-frequency magnetic fields can induce unwanted voltages in amplifier wiring and transformer circuits.

• A. Gives distorted output
• B. Gives low power output
• C. Requires a transformer
• D. None of the above

Explanation: Impedance matching can introduce waveform distortion, especially when transformer or tuned matching networks have a limited frequency…

• A. RC
• B. Direct
• C. Impedance
• D. Transformer

Explanation: Transformer coupling is generally the most costly because it requires a specially designed transformer, which adds material, manufacturing…

• A. AF amplifiers
• B. Detectors
• C. amplifiers
• D. None of the above

Explanation: A class C stage conducts for less than half of the input cycle, so it is unsuitable for faithful audio amplification but useful as a tuned…

• A. Mixer stage
• B. Power stage
• C. Detector stage
• D. F stage

Explanation: The output stage must deliver substantial current and power to the load, so it is called the power stage.

• A. C
• B. A
• C. B
• D. AB

Explanation: Class C has the highest theoretical collector efficiency because its transistor conducts for less than 180 degrees and a tuned circuit…

• A. 5%
• B. 50%
• C. 30%
• D. 25%

Explanation: For a resistance-loaded class A amplifier, the maximum AC output power is one-quarter of the DC input power, giving a maximum efficiency…

• A. Transformer
• B. RC
• C. direct
• D. Impedance

Explanation: Transformer coupling is commonly used in power amplifiers because the transformer can match the transistor's high output impedance to a…

• A. Small
• B. Very small
• C. Large
• D. None of the above

Explanation: Power amplifiers are designed to deliver large voltage and current, hence substantial power, to the load.

• A. 30%
• B. 50%
• C. 80%
• D. 45%

Explanation: A transformer-coupled class A amplifier can achieve 50% maximum efficiency because the transformer isolates the DC supply from the load…

• A. At cut off point
• B. At the middle
• C. At saturation point
• D. None of the above

Explanation: For class A operation, the transistor conducts throughout the complete input cycle, so the quiescent point is placed near the middle of…

• A. Class A
• B. Class B
• C. Class C
• D. None of the above

Explanation: A 60° conduction angle is less than 180°, so the transistor conducts for only a small part of the input cycle.

• A. Symmetrical
• B. Single-ended
• C. Reciprocating
• D. Differential

Explanation: A class A power amplifier commonly uses one transistor that conducts for the entire cycle, so it is called a single-ended amplifier.

• A. Dual
• B. Push-pull
• C. Symmetrical
• D. Differential

Explanation: In a two-transistor class B stage, the transistors conduct on alternate half-cycles and combine their outputs, forming a push-pull…

• A. Small
• B. Large
• C. Very large
• D. None of the aboveElectricity

Explanation: Power transistors generally have comparatively small current gain β because they are designed to handle large currents and dissipate…

• A. Low forward bias
• B. Less battery consumption
• C. More battery consumption
• D. None of the above

Explanation: Low efficiency means a larger portion of the supplied battery power is wasted as heat instead of being delivered to the load.