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Semiconductor Electronics is almost pure recall. There is very little to calculate and a lot to remember exactly. That is good news, because a student who learns it properly never loses these marks. Ten questions below, with the answer key and a hint for each.
What this chapter carries in NEET(UG)
- Usually 2 to 3 questions every year, which is 8 to 12 marks.
- Most of them come from doping, the p-n junction, diodes, rectifiers and logic gates.
- Nearly every question here is answered from memory, not from a formula.
What the syllabus says
In the syllabus (Unit 19, Electronic Devices): Semiconductors, the semiconductor diode and its I–V characteristics in forward and reverse bias, the diode as a rectifier, I–V characteristics of the LED, the photodiode, the solar cell and the Zener diode, the Zener diode as a voltage regulator, and logic gates — OR, AND, NOT, NAND and NOR.
Taken out in 2024: the junction transistor, transistor action and transistor characteristics; the transistor as an amplifier in common emitter configuration and as an oscillator; the transistor as a switch; energy bands in solids, and the band picture of conductors, insulators and semiconductors.
Taken from the NMC syllabus for NEET (UG) 2026, the latest one published. See the full syllabus, unit by unit.
Formulas you must know by heart
| Pure (intrinsic) semiconductor | ne = nh |
| Doping with a pentavalent atom | gives n-type, electrons are the majority carriers |
| Doping with a trivalent atom | gives p-type, holes are the majority carriers |
| Forward bias | p side to positive, low resistance, current flows |
| Reverse bias | p side to negative, high resistance, almost no current |
| Half-wave rectifier | uses one diode, output for half the cycle |
| Full-wave rectifier | uses two diodes (or four in a bridge), output for the whole cycle |
| Energy gap | conductor ≈ 0, semiconductor ≈ 1 eV, insulator > 3 eV |
| Temperature effect | resistance of a semiconductor falls as temperature rises |
Learn the two doping cases cold. Pentavalent gives n-type, trivalent gives p-type. Most mistakes in this chapter start there.
Ten questions. Give yourself ten minutes.
Write your answers down before you scroll. A question you looked up is a question you have not answered.
Q1. A semiconductor doped with a pentavalent impurity becomes
- (a) p-type
- (b) n-type
- (c) intrinsic
- (d) an insulator
Q2. In a p-type semiconductor, the majority charge carriers are
- (a) electrons
- (b) holes
- (c) protons
- (d) neutrons
Q3. In a pure semiconductor at room temperature, the number of free electrons compared with the number of holes is
- (a) greater
- (b) smaller
- (c) equal
- (d) zero
Q4. A p-n junction diode is forward biased when the p side is connected to the
- (a) positive terminal
- (b) negative terminal
- (c) either terminal
- (d) earth
Q5. The number of diodes needed for a half-wave rectifier is
- (a) one
- (b) two
- (c) three
- (d) four
Q6. A full-wave bridge rectifier uses
- (a) one diode
- (b) two diodes
- (c) three diodes
- (d) four diodes
Q7. As the temperature of a semiconductor is raised, its electrical resistance
- (a) increases
- (b) decreases
- (c) stays the same
- (d) first rises and then falls
Q8. The forbidden energy gap of a typical semiconductor is about
- (a) 0 eV
- (b) 1 eV
- (c) 6 eV
- (d) 100 eV
Q9. The logic gate that gives an output 1 only when both inputs are 1 is
- (a) OR
- (b) AND
- (c) NOT
- (d) NOR
Q10. A reverse-biased p-n junction has
- (a) low resistance and large current
- (b) high resistance and very small current
- (c) zero resistance
- (d) infinite current
Answer key, with a hint for each
| Q1 | (b) | A pentavalent atom brings a spare electron, so the material becomes n-type. |
| Q2 | (b) | In p-type the holes are in the majority. Electrons are the minority there. |
| Q3 | (c) | In an intrinsic semiconductor every free electron leaves a hole behind, so the two numbers match. |
| Q4 | (a) | Forward bias means p to positive and n to negative. |
| Q5 | (a) | One diode is enough. It conducts for one half of each cycle. |
| Q6 | (d) | A bridge uses four diodes. The older centre-tap design uses two. |
| Q7 | (b) | More electrons are freed at higher temperature, so resistance falls. This is the opposite of a metal. |
| Q8 | (b) | About 1 eV. Silicon is roughly 1.1 eV and germanium about 0.7 eV. |
| Q9 | (b) | AND gives 1 only when every input is 1. |
| Q10 | (b) | Reverse bias widens the depletion layer, so resistance is high and only a tiny leakage current flows. |
Now mark yourself honestly
NEET(UG) marks the way it marks. Use the same rule here:
- +4 for a right answer
- −1 for a wrong one
- 0 for a blank
So ten questions here are out of 40. In the real paper, 45 Physics questions are out of 180.
If you scored 32 or more, the basics of this chapter are secure. Move to harder questions, not more of these.
If you scored below 24, do not feel bad about it. You have just found out something useful before the exam did. Go back to the formula table above, learn it properly, and sit these ten again tomorrow.
And if you guessed a few and they landed, count those as wrong. A guess that works once will not work in May.
The full chapter, on a clock
Ten questions tell you a little. Forty-five tell you the truth.
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