These MCQs are based on previous year questions (PYQs) of SSC JE Electrical. Perfect for quick revision and test practice.
✅ 1. Which device is commonly used as a controlled switch in power electronics?
A. BJT
B. SCR
C. MOSFET
D. UJT
Answer: ✅ B. SCR
Explanation: SCR (Silicon Controlled Rectifier) is widely used in power control applications due to its controllability and high voltage handling.
✅ 2. A single-phase full-wave bridge rectifier uses how many diodes?
A. 2
B. 4
C. 3
D. 6
Answer: ✅ B. 4
Explanation: A full-wave bridge rectifier uses four diodes arranged in a bridge configuration.
✅ 3. In a chopper circuit, output voltage can be controlled by:
A. Input frequency
B. Output frequency
C. Duty cycle
D. Load resistance
Answer: ✅ C. Duty cycle
Explanation: By varying the duty cycle (ON/OFF time ratio), the average output voltage of a chopper can be controlled.
✅ 4. The input power factor of a fully-controlled rectifier is:
A. Unity
B. Leading
C. Lagging
D. Depends on firing angle
Answer: ✅ D. Depends on firing angle
Explanation: As the firing angle increases, the power factor decreases due to the delay in current conduction.
✅ 5. Which of the following is used for speed control of DC motors?
A. Rectifier
B. Inverter
C. Chopper
D. Cycloconverter
Answer: ✅ C. Chopper
Explanation: Choppers control the voltage applied to a DC motor, hence regulating its speed.
✅ 6. Inverters convert:
A. DC to AC
B. AC to DC
C. AC to AC
D. DC to DC
Answer: ✅ A. DC to AC
Explanation: Inverters are used to convert DC supply into AC output.
✅ 7. What is the main function of a snubber circuit across SCRs?
A. Speed control
B. Harmonic reduction
C. Protection from overvoltage
D. Provide triggering pulse
Answer: ✅ C. Protection from overvoltage
Explanation: Snubber circuits protect SCRs from dv/dt triggered false turn-on and voltage spikes.
✅ 8. Which motor is most suitable for variable frequency drive (VFD) control?
A. Synchronous motor
B. DC shunt motor
C. Induction motor
D. Stepper motor
Answer: ✅ C. Induction motor
Explanation: Induction motors are robust, inexpensive, and compatible with VFD control.
✅ 9. Cycloconverter is a device that converts:
A. DC to AC
B. AC to DC
C. AC to AC (lower frequency)
D. DC to DC
Answer: ✅ C. AC to AC (lower frequency)
Explanation: Cycloconverters directly convert AC at one frequency to AC at a lower frequency.
✅ 10. Which characteristic is not typical of IGBT compared to MOSFET?
A. High input impedance
B. High switching speed
C. Voltage-controlled device
D. Low conduction loss
Answer: ✅ B. High switching speed
Explanation: IGBTs have lower switching speed than MOSFETs but better conduction efficiency in high-power applications.
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