An ideal diode is reverse biased in series with a 1.0 kΩ resistor across a 10 V battery. What is the potential difference across the resistor?
Correct answer A. Approximately 0 V
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Electronics MCQs
Electronics MCQs cover n-type and p-type semiconductors, the PN junction in forward and reverse bias, diode voltages and half-wave and full-wave rectification with smoothing. They help MDCAT, ECAT and FSc candidates revise the basics of semiconductor devices, and every question on MCQs360 shows its correct answer instantly.
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An ideal full-wave rectifier gives output pulses of peak value 10 V. What is the average (DC) output voltage (Average = 2V₀/π)?
Correct answer A. 6.37 V
An ideal half-wave rectifier gives output pulses of peak value 31.4 V. What is the average (DC) value of the output (Average = V₀/π)?
Correct answer C. 10.0 V
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A 1:10 step-down transformer connected to 230 V rms mains feeds an ideal half-wave rectifier. What is the peak output voltage?
Correct answer B. 32.5 V
Two silicon diodes (0.7 V each) are connected in series, both forward biased, with a 230 Ω resistor across a 3.0 V supply. What is the current?
Correct answer D. 7.0 mA
A full-wave rectifier is fed from a 60 Hz supply. How many output pulses are produced each second?
Correct answer B. 120
In a centre-tapped full-wave rectifier, each half of the secondary winding has a peak voltage of 15 V. What peak inverse voltage must each ideal diode withstand?
Correct answer D. 30 V
A germanium diode (0.3 V drop) and a resistor are connected in series across a 9.0 V battery so that 20 mA flows in forward bias. What is the resistance?
Correct answer D. 435 Ω
A forward-biased silicon diode (0.7 V drop) is connected in series with a 430 Ω resistor across a 5.0 V supply. What current flows?
Correct answer B. 10 mA
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A bridge rectifier uses silicon diodes (0.7 V each) and its transformer secondary gives 12 V rms. What is the approximate peak output voltage across the load?
Correct answer B. 15.6 V
A full-wave rectifier is fed from 50 Hz mains. What is the frequency of the ripple in its output?
Correct answer B. 100 Hz
Which statement correctly compares the resistance of a PN junction diode in its two bias conditions?
Correct answer B. Low in forward bias and very high in reverse bias
A half-wave rectifier is fed from 50 Hz mains. What is the frequency of the ripple in its output?
Correct answer B. 50 Hz
Which is an advantage of full-wave rectification over half-wave rectification?
Correct answer B. It gives a higher average output with less ripple
The depletion region of an unbiased PN junction contains mainly ____
Correct answer A. immobile positive and negative ions
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How does the reverse saturation current of a PN junction change when its temperature rises?
Correct answer B. It increases
Boron added to silicon acts as which kind of impurity?
Correct answer C. An acceptor impurity producing holes
Adding a small amount of phosphorus to pure silicon produces which type of semiconductor?
Correct answer D. n-type
The output of a rectifier without any filter is best described as ____
Correct answer B. pulsating DC
Why is a capacitor connected in parallel with the load of a rectifier?
Correct answer D. To smooth the pulsating output
About Electronics MCQs
Questions start with doping: which impurities produce n-type and p-type material and what the majority charge carriers are. PN junction questions cover the depletion region, potential barrier, forward and reverse bias, the turn-on voltages of silicon and germanium diodes and the effect of temperature on reverse saturation current. Circuit MCQs ask you to find current through forward-biased diodes in series with a resistor. Rectifier questions compare half-wave, centre-tap and bridge circuits, count how many diodes conduct per half-cycle, find peak output voltage after a transformer and explain why a smoothing capacitor is connected across the load.
Key facts to remember
- Adding a pentavalent impurity (such as phosphorus or arsenic) to silicon gives an n-type semiconductor; a trivalent impurity (such as boron or gallium) gives p-type.
- A PN junction is forward biased when the p-side is connected to the positive terminal; it then conducts.
- The forward voltage drop is about 0.7 V for a silicon diode and about 0.3 V for germanium.
- A half-wave rectifier uses one diode; a bridge rectifier uses four, with two conducting in each half-cycle.
- Peak voltage V₀ = √2 × V_rms, and a capacitor in parallel with the load smooths the rectified output.
- Reverse saturation current of a PN junction increases as temperature rises.
Exams that include Electronics MCQs
Pakistan
- MDCAT
- ECAT (UET)
- NUMS
- AKU
- FSc boards
India
- NEET
- JEE Main
Bangladesh
- HSC
- Medical Admission Test
How to prepare for Electronics MCQs
- Memorise the dopant groups: Group 15 elements give n-type, Group 13 elements give p-type.
- In diode circuit calculations, subtract the diode drops from the supply before dividing by the resistance.
- Draw a bridge rectifier and trace the current for each half-cycle to see which pair of diodes conducts.
- When a transformer feeds a rectifier, convert the secondary rms voltage to its peak value with √2.
Frequently asked questions
Which exams ask Electronics MCQs?
Electronics is part of the FSc physics syllabus, so its MCQs appear in MDCAT, ECAT (UET), NUMS and AKU entry tests and in FSc board papers. Students in India meet the same ideas in NEET and JEE Main, and Bangladeshi students in HSC and the medical admission test.
What is the difference between forward and reverse bias?
In forward bias the p-side of a PN junction is connected to the positive terminal, the depletion region narrows and current flows once the barrier voltage is overcome. In reverse bias the p-side is connected to the negative terminal, the depletion region widens and only a tiny leakage current flows.
Last reviewed October 2026