Free Electronics 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. direct current to alternating current
• B. alternating current to direct current
• C. low voltage to high voltage
• D. current to voltage

Explanation: A diode conducts in one direction only, so it can strip out one half of the alternating cycle and leave a unidirectional output.

• A. uses both halves of the input cycle
• B. consists of one half cycle only, with the other half missing
• C. is a steady direct voltage
• D. is zero

Explanation: The single diode conducts only while its anode is positive, so alternate half cycles are blocked and the output is a series of pulses with…

• A. one diode
• B. two diodes
• C. four diodes
• D. no diodes

Explanation: Four diodes arranged in a bridge route both halves of the cycle through the load in the same direction, so the output has twice the pulse…

• A. an amplifier
• B. a smoothing element, charging at the peaks and discharging between them to reduce ripple
• C. a switch
• D. an oscillator

Explanation: The capacitor stores charge while the rectified voltage rises and releases it while the voltage falls, filling in the troughs so the…

• 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. 25 Hz
• B. 50 Hz
• C. 100 Hz
• D. 200 Hz

Explanation: Both halves of each cycle produce an output pulse, so there are two pulses per input cycle and the ripple appears at twice the supply…

• 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…