Chapter 49 · 450 practice MCQs
MDCAT Electronics MCQs 2026 | Rectification & PN Junction
A diode is a one-way street. Unit 13 in this bank is PMDC 13.1 rectification and 13.2 the PN junction — no transistors, no gates, forty questions on the two outcomes the paper actually names.
·5 min read·Usman Ubaid
What MDCAT 2026 asks in Unit 49 Electronics
PMDC’s electronics unit is wider in some FSc books than in the MDCAT outcome list. Physics Lab follows 13.1 and 13.2 only: the PN junction and rectification. There are no transistors, no logic gates, no amplifiers in this quiz. That is how you revise without leaking into next year’s rumours.
PN join: diffusion of majority carriers, a depletion region, a barrier field from n toward p. Forward bias (p to +) narrows the barrier; reverse widens it. Silicon knee ≈ , germanium ≈ . Bulk p and n are named for the majority carrier, not for net charge — they are still neutral.
Half-wave: one half through, the other gone. Pulse frequency stays f. = Vm/ . Full-wave: both halves, = 2f, = 2Vm/ . Bridge uses four diodes; centre-tap uses two plus a tap. PIV is the peak the diode must survive when it is off. Forty MCQs, forty labs — twice the usual unit.
- PN junction: depletion, barrier n → p, forward narrows, reverse widens.
- Half-wave: = Vm/ = f.
- Full-wave: = 2Vm/ = 2f.
- Bridge: four diodes. Centre-tap: two diodes and a tapped secondary.
- PIV: the reverse peak the off diode must stand.
Often-asked Electronics MCQ patterns
These are the Electronics ideas that keep coming every year with new numbers.
- A transformer that rectifies — it does not. It only changes AC voltage.
- Half-wave doubling frequency.
- Forward bias thickening the barrier.
- Calling bulk p and n ‘charged’.
- Vm/ and 2Vm/ swapped.
- Bridge drawn with two diodes.
Worked Electronics numericals (
Work these on paper first. Then open the Unit 49 quiz — the same numbers are in the questions, with wrong options built from the usual mix-ups.
Same peak Vm. Compare for half-wave and full-wave.
- Half-wave: = Vm/ .
- Full-wave: = 2Vm/ — twice the humps, twice the average.
- is f versus 2f. That is a separate item.
Full-wave has the higher DC output and double the ripple frequency.
p-side connected to the positive of a battery. Barrier?
- This is forward. The battery fights the barrier field.
- Depletion narrows. Current (after the knee) is large.
Barrier thins. Reverse does the opposite — and the current is the tiny reverse saturation.
Electronics traps that steal the mark
A good option is a true sentence about the wrong quantity. If you miss, the quiz names the mix-up on the option you actually picked.
- A transformer that rectifies.
- Half-wave doubling frequency.
- Forward bias thickening the barrier.
- Calling bulk p and n ‘charged’ — they are named for the majority carrier, not net charge.
- Swapping Vm/ with 2Vm/ .
- Putting transistors in a 13.1–13.2 revision list.
Electronics formula sheet for MDCAT 2026
Write these until they are cheaper than thinking. Then open the Electronics quiz and make the picture agree.
- half-wave = Vm/
- full-wave = 2Vm/
How to practise Unit 49 Electronics MCQs
Draw the AC humps. Shade what the diode lets through. Count humps per second — that is . Average the shade — that is .
On PN items, write ‘majority’ and ‘barrier direction n → p’ before you touch bias. Forward is p to +.
This unit is two quizzes of twenty. Junction first, rectifiers second — or the other way around.
Choose topics and a test length up to 180 from the 450-question bank. Tutor Mode explains each selection; Timed Exam reveals explanations on submission. Use the complete review to revise mistakes and download your results.
FAQ
Common questions
Half-wave or full-wave — which has the higher DC output?
Full-wave. Same peak, twice the humps: 2Vm/ against Vm/ . These average-output expressions assume ideal rectification without a smoothing capacitor. For the same input frequency, full-wave rectification also doubles the ripple frequency.
Does a transformer rectify AC?
No. A transformer changes AC voltage. Diodes rectify. Mixing the two is a Unit 11/13 trap. An ordinary transformer needs changing magnetic flux for continuous induction. A diode rectifier converts alternating input into a unidirectional output; these are different circuit functions.
What is PIV in MDCAT electronics?
Peak inverse voltage — the maximum reverse voltage a diode must survive while it is off in the rectifier. The required rating depends on rectifier topology and peak input voltage. Exceeding the reverse-voltage rating can cause diode breakdown, so distinguish PIV from forward voltage drop.
Silicon vs germanium knee voltage?
Si ≈ , Ge ≈ . Forward current is still tiny below the knee. The and values are approximate circuit models, not abrupt physical switches. Actual current depends on voltage, temperature and the particular diode.
How many Electronics MCQs are available on DIFF. MDCAT?
The current Electronics question bank contains 450 practice MCQs across 2 topics. This is the bank size, not the length of one test. Choose your topics and a question count from 1 to 180, limited by the questions available in those topics.
Which topics does the Electronics quiz cover?
The selectable topics are Rectification, PN Junction. Use Select all for a broad chapter drill, Clear to start a focused selection, or choose individual topics. Questions are drawn from your chosen topics, so you can target a weak concept before returning to a wider test.
How do I build a custom Electronics test?
Open the chapter builder, select one or more topics, enter your question count, and choose Tutor Mode or Timed Exam. The available-question total updates with your selection. Start Test generates a shuffled drill; you do not have to follow a fixed Quiz 1 or Quiz 2 sequence.
What is the difference between Tutor Mode and Timed Exam?
Tutor Mode gives feedback and an explanation after you choose an option, and you can change or clear that choice. Timed Exam runs a countdown and keeps explanations hidden until submission. Both modes let you move between questions, use the paper map, and submit for a complete review.
How do I review and download my Electronics quiz?
Select Submit Quiz, then Submit & View Explanations. The review includes every question in your test, all options, your selection, the marked correct answer when a key is available, and the explanation. Download PDF saves a paginated review; Download Review saves an HTML copy you can open in a browser. The review also includes DIFF. MDCAT community links.
How should I use Electronics MCQs to improve?
Start with a short tutor drill on one of these topics: Rectification, PN Junction. Read the explanation for incorrect and uncertain answers, revise the relevant textbook section, and retry before taking a timed drill. Compare your reasoning with the answer key rather than memorising the option letter.
Ready to sit Unit 49 Electronics — 450 MCQs, 450 labs?