Free PN Junction MCQs with Answers

• A. n type, with electrons as the majority carriers
• B. p type, with holes as the majority carriers
• C. an insulator
• D. a conductor with no charge carriers

Explanation: A pentavalent atom has five valence electrons but only four are needed for bonding, so the fifth is loosely bound and becomes a free…

• A. electrons
• B. holes
• C. protons
• D. neutrons

Explanation: Trivalent dopants create vacancies in the bonding structure, and these holes behave as mobile positive charges as neighbouring electrons…

• A. contains a very high concentration of free carriers
• B. has been swept clear of mobile charge carriers, leaving fixed ions and a potential barrier
• C. conducts better than the rest of the crystal
• D. consists only of electrons

Explanation: Electrons diffusing across the junction recombine with holes, leaving exposed fixed ions on both sides and a region with almost no mobile…

• A. the p side is connected to the positive terminal and the n side to the negative
• B. the n side is connected to the positive terminal
• C. both sides are connected to the same terminal
• D. no voltage is applied

Explanation: Connecting positive to p repels holes and negative to n repels electrons, driving both towards the junction, so the depletion layer…

• A. large
• B. the same as in forward bias
• C. almost zero, apart from a small leakage current
• D. infinite

Explanation: The widened depletion region blocks the majority carriers, leaving only the thermally generated minority carriers to cross, which gives a…

• A. 0.3 V
• B. 0.7 V
• C. 5 V
• D. 12 V

Explanation: Silicon has a barrier of roughly 0.7 V, while germanium's is about 0.3 V, which is why a silicon diode needs about 0.7 V across it before…

• A. in forward bias as a rectifier
• B. in reverse bias at its breakdown voltage, as a voltage regulator
• C. with no bias at all
• D. only at very high frequency

Explanation: Beyond the breakdown voltage a Zener conducts heavily while the voltage across it stays almost constant, which makes it a simple and…

• A. it is reverse biased and breaks down
• B. it is forward biased and electrons recombine with holes, releasing energy as photons
• C. it is heated
• D. current passes through a filament inside it

Explanation: Each recombination across the junction releases an energy equal to the band gap of the semiconductor, and in materials such as gallium…

• A. heat the junction
• B. create extra electron hole pairs, increasing the reverse current
• C. reduce the leakage current to zero
• D. change the doping of the material

Explanation: Photons with enough energy free electrons across the band gap in the depletion region, so the reverse current rises in proportion to the…

• A. far fewer free charge carriers, and a conductivity that rises with temperature
• B. more free carriers
• C. the same number of carriers
• D. no carriers at any temperature

Explanation: A pure semiconductor has a small energy gap, so only a few electrons have enough thermal energy to cross it at room temperature, but…

• A. a conductor
• B. a semiconductor
• C. an insulator
• D. all three equally

Explanation: An insulator has a gap of several electron volts, far more than thermal energy can supply, so almost no electrons reach the conduction…

• A. electrons
• B. holes
• C. protons
• D. positive ions

Explanation: Doping supplies a large number of electrons, but thermal generation still creates a small population of holes, and these minority carriers…

• A. has a lower barrier potential
• B. tolerates higher temperatures and has a much smaller leakage current
• C. is a better conductor
• D. requires no doping

Explanation: Silicon's larger band gap means far fewer thermally generated carriers, so leakage is low and devices work reliably at higher…

• A. no change in the collector current
• B. a much larger change in the collector current
• C. a smaller change in the collector current
• D. a change only in the emitter voltage

Explanation: The current gain of a common emitter transistor is typically between 50 and 300, so a weak input signal at the base controls a much larger…

• A. forward biased and reverse biased
• B. both forward biased
• C. both reverse biased
• D. reverse biased and forward biased

Explanation: Forward bias on the emitter base junction injects carriers into the thin lightly doped base, and the reverse biased collector base…

• A. Diode
• B. Resistor
• C. Photodiode
• D. Capacitor

Explanation: An LED is a p-n junction that emits light when forward biased, while a photodiode is designed to detect light and is commonly operated in…

• A. The light emitting diodes
• B. Photo diodes
• C. Photo voltaic cell
• D. Solar cells.

Explanation: A photodiode is a semiconductor diode designed to respond rapidly to incident light, so it can convert light pulses into electrical pulses…

• A. n-carriers only
• B. p-carriers only
• C. p-carriers and n-carriers respectively
• D. n-carriers and p-carriers respectively

Explanation: A trivalent acceptor impurity creates holes, which are p-type carriers, while a pentavalent donor impurity contributes extra electrons…

• A. Logic gates
• B. Boolean algebra
• C. Amplifier gain
• D. Logic functions

Explanation: Logic gates are electronic circuits designed to perform Boolean operations such as AND, OR, and NOT on binary signals.

• A. Increases
• B. Decreases
• C. Remains same
• D. No effect

Explanation: Forward bias opposes the built-in electric field of a p-n junction, reducing the depletion-layer width and lowering the potential barrier.