Free Electronics and Devices MCQs with Answers

• A. Free electrons
• B. Holes
• C. Valence electrons
• D. Bound electrons

Explanation: A pentavalent impurity has five valence electrons; four form covalent bonds and the fifth becomes a loosely bound conduction electron.

• A. Goes up
• B. Goes down
• C. Remains the same
• D. Can't sayHire Civil Engineers

Explanation: Heating a pure semiconductor generates more electron-hole pairs, sharply increasing its conductivity.

• A. 2
• B. 3
• C. 6
• D. 4

Explanation: Common elemental semiconductors such as silicon and germanium have four valence electrons.

• A. Positive
• B. Zero
• C. Negative
• D. None of the aboveCompare Local Schools

Explanation: A semiconductor has a negative temperature coefficient because heating increases the number of charge carriers and therefore increases…

• A. 90 V/µs
• B. 0.67 V/µs
• C. 1.5 V/µs
• D. none of these

Explanation: Slew rate is the maximum rate of output-voltage change: SR = ΔV/Δt = 8/12 = 0.67 V/µs. Thus, option b gives the calculated value.

• A. increases the input and output impedances
• B. increases the input impedance and bandwidth
• C. decreases the output impedance and bandwidth
• D. does not affect impedance or bandwidth

Explanation: For the usual voltage-series negative feedback used in op-amp circuits, input impedance and bandwidth increase, while output impedance…

• A. r'e
• B. r'e/2
• C. 2r'e
• D. RE

Explanation: For a BJT differential amplifier with a single-ended output, the differential gain magnitude is approximately A_d = R_C/(2r′_e).

• A. r'e
• B. 2r'e
• C. r'e/2
• D. 2RE

Explanation: For common-mode operation, both transistor currents change together, so the effective emitter resistance is approximately 2R_E.

• A. smaller than differentail voltage gain
• B. equal to differential voltage gain
• C. greater than differential voltage gain
• D. none of the above

Explanation: A differential amplifier is designed to amplify the difference between inputs while rejecting signals common to both, so its common-mode…

• A. ß
• B. RE
• C. RC
• D. 2ß

Explanation: For a balanced differential pair, the two transistor input resistances appear in series for differential excitation, giving an input…

• A. collector supply voltage
• B. zero
• C. emitter supply voltage
• D. tail current times base resistance

Explanation: With balanced inputs, the common-emitter node remains nearly at virtual ground, so the voltage at the top of the tail resistor is close to…

• A. a.c. signals only
• B. d.c. signals only
• C. both a.c. and d.c. signals
• D. neither d.c. nor a.c. signals

Explanation: An op-amp responds to the voltage difference at its inputs regardless of whether the signal is varying or steady, within its operating…

• A. 100,000
• B. 1000
• C. 101
• D. 100

Explanation: For a non-inverting amplifier, the closed-loop gain is 1 + Rf/Ri. Substituting the values gives 1 + 100 kΩ/1 kΩ = 101.

• A. equal to the input
• B. increased
• C. fed back to the inverting input
• D. fed back to the noninverting input

Explanation: Negative feedback returns a portion of the output to the inverting input, opposing the input signal and stabilising the gain.

• A. very high
• B. very low
• C. always unity
• D. unpredictable

Explanation: Common-mode signals are unwanted signals appearing equally at both inputs, and a differential amplifier is designed to reject them.

• A. opposite polarity signals are applied to the inputs
• B. the gain is one
• C. the outputs are of different amplitudes
• D. only one supply voltage is used

Explanation: Differential-mode operation applies equal signals with opposite polarity to the two inputs, so the amplifier responds to their difference.

• A. very high
• B. very low
• C. dependent on input voltage
• D. about 100

Explanation: An op-amp's differential gain is designed to be very large so even a small voltage difference between its inputs can produce a substantial…

• A. the output is grounded
• B. one input is grounded and signal is applied to the other
• C. both inputs are connected together
• D. the output is not inverted

Explanation: Single-ended operation applies the signal to one input while the other input is grounded or held at a reference potential.

• A. equal to the positive supply voltage
• B. equal to the negative supply voltage
• C. equal to zero
• D. equal to CMRR

Explanation: With equal zero-voltage inputs, the ideal differential input voltage is zero, so the ideal op-amp output is also zero.

• A. both inputs are grounded
• B. the outputs are connected together
• C. an identical signal appears on both the inputs
• D. the output signal are in-phase

Explanation: Common-mode operation means the same voltage signal is applied simultaneously to both inputs.