Free Electronics and Devices MCQs with Answers

• A. Is relatively inexpensive
• B. Does not require moving contacts
• C. Combines control with power amplification
• D. None of the above

Explanation: A relay lets a low-power control circuit operate a separate higher-power load, providing switching gain and often electrical isolation.

• A. Monostable
• B. Astable
• C. Bistable
• D. None of the above

Explanation: An astable multivibrator repeatedly switches between its two states without external triggering, producing a continuous square wave.

• A. VCC
• B. 0
• C. VCC/2
• D. 2VCC

Explanation: In a common-emitter transistor switch, saturation drives the collector-emitter voltage close to zero, so the output is ideally 0 V.

• A. Electronic
• B. Mechanical
• C. Electromechanical
• D. None of the above

Explanation: Electronic switches, such as transistor switches, are generally the least expensive because they have no moving parts and can be…

• A. One state
• B. Two states
• C. Three states
• D. None of the above

Explanation: A switch has two stable operating states: open, which interrupts current, and closed, which permits current to flow.

• A. 104
• B. 10
• C. 1000
• D. 109

Explanation: Electronic switches can operate at extremely high speeds because they have no mechanical inertia, with practical maximum rates reaching…

• A. Is operated mechanically
• B. Is costly
• C. Has high inertia
• D. None of the above

Explanation: A mechanical switch contains moving parts, so its inertia limits switching speed and causes contact bounce and wear.

• A. Electronic
• B. Mechanical
• C. Electromechanical
• D. None of the above

Explanation: An electronic switch operates without moving contacts, allowing it to switch much faster than mechanical or electromechanical types.

• A. 10 O
• B. 50 O
• C. 25 O
• D. 40 O

Explanation: The two zeners require 30 V total, leaving 45 - 30 = 15 V across the resistor. At the 300 mA maximum current, R = 15/0.3 = 50 ohms.

• A. Zero
• B. Minimum
• C. Maximum
• D. None of the above

Explanation: With zero load current, the source current flows almost entirely through the zener, so the zener current is maximum.

• A. 10 O
• B. 20 O
• C. 15 O
• D. 40 O

Explanation: At the maximum rated current, the smallest permissible resistance is given by Ohm’s law: R = V/I = 20/0.5 = 40 Ω.

• A. Increases the ripple
• B. Decreases the ripple
• C. Neither increases nor decreases the ripple
• D. Data insufficient

Explanation: A Zener regulator holds the output voltage nearly constant, so variations in the rectifier output appear less at the load as ripple.

• A. Load current is maximum
• B. Load current is minimum
• C. Load current is zero
• D. None of the above

Explanation: The Zener current is approximately the series current minus the load current, so it becomes minimum when the load draws its maximum…

• A. 15 V
• B. 5 V
• C. 30 V
• D. 45 V

Explanation: For similar Zener diodes in series, their breakdown voltages add: 15 V + 15 V = 30 V.

• A. 10%
• B. 20%
• C. 15%
• D. 5%

Explanation: For an ordinary unregulated supply, the DC output changes approximately in proportion to the input, so a 5% input increase gives about a…

• A. Forward biased
• B. Unbiased
• C. Reverse biased
• D. Operating in the breakdown region

Explanation: A Zener diode provides voltage regulation when reverse biased in its breakdown region, where large current changes cause only a small…

• A. Increases
• B. Decreases
• C. Stays the same
• D. None of the above

Explanation: Increasing the load current increases the voltage drop across the supply’s internal resistance and transformer or filter resistance.

• A. Series current
• B. Zener current
• C. Load current
• D. None of the above

Explanation: The series current splits into load and Zener currents, so I_S = I_L + I_Z.

• A. It is a diode
• B. It is a constant current device
• C. It is a constant-voltage device
• D. It works in the forward region

Explanation: A Zener diode is chiefly used in reverse breakdown, where its voltage remains nearly constant over a useful current range.

• A. Decreases
• B. Stays the same
• C. Increases
• D. None of the above

Explanation: When load resistance decreases, load current increases; with the series current approximately fixed, less current remains for the Zener.