Electronic Devices : Practice Questions and Answers

The correct answer is C: 4.

A bridge rectifier is a full-wave rectifier that converts AC input to DC output using four diodes arranged in a bridge configuration.

Working Principle:

• Positive half-cycle: Diodes D1 and D2 conduct; D3 and D4 are in reverse bias.
• Negative half-cycle: Diodes D3 and D4 conduct; D1 and D2 are in reverse bias.
• Current always flows in the same direction through the load, producing unidirectional DC output.

Advantages:

• Utilizes both halves of the AC waveform (full-wave rectification).
• Higher output voltage and power than half-wave rectifiers.
• Lower ripple frequency, easier to filter.

Disadvantages:

• Two diodes always in the conducting path cause a voltage drop of ~1.4V (2 × 0.7V).
• Requires four diodes vs. one in a half-wave rectifier.

Applications: Power supply circuits, battery chargers, and AC-to-DC conversion in electronic equipment.

The correct answer is B: Emitter.

In the common emitter (CE) configuration, the emitter terminal is common to both the input and output circuits — hence the name.

• Input: Applied between the base and emitter terminals.
• Output: Taken between the collector and emitter terminals.
• A small base current controls a much larger collector-to-emitter current, enabling amplification.

Advantages of Common Emitter Configuration:

• High voltage gain — suitable for amplification applications.
• High current gain — efficient control of output current with small input current.
• Inverts the input signal (180° phase shift).

Disadvantages:

• Lower input impedance compared to common base or common collector configurations.
• Relatively high output impedance.

Applications:

• Audio and radio frequency amplifiers.
• Digital switching circuits.

The correct answer is C.

Concept: The energy released or absorbed during a phase change is given by E = mL, where m is the mass of the substance and L is the latent heat.

Derivation:

• Energy required to convert ice to water: mL = 1000 g × 80 cal/g = 80,000 cal
• Total energy delivered by the photon source in time T: E = nT × hν
• Setting them equal: nThν = mL
• Therefore: T = mL / (nhν)

From this expression:

• T ∝ 1/n when ν is constant — so T decreases as n increases (Option 1 is incorrect).
• T ∝ 1/ν when n is constant — so T decreases as ν increases (Option 2 is incorrect).
• If nν = constant, then T = mL / (h × nν) = constant — T remains unchanged (Option 3 is correct).
• If nν increases, T decreases, not increases (Option 4 is incorrect).