Free Electronics and Devices MCQs with Answers

• A. current
• B. voltage
• C. both voltage and current
• D. none of the above

Explanation: A transistor is commonly described as a current-operated device because its output collector current is controlled by the base current.

• A. 10
• B. 1
• C. 01
• D. 15

Explanation: The feedback fraction is β = V_f/V_o = 0.1/10 = 0.01. Thus the feedback voltage is one-hundredth of the output voltage, not 0.1 or 1.

• A. collector
• B. base
• C. emitter
• D. collector-base-junction

Explanation: The collector is made largest because it must dissipate the transistor's heat and withstand a relatively high reverse-bias voltage.

• A. Damped
• B. Undamped
• C. Modulated
• D. None of the above

Explanation: An ideal oscillator produces undamped oscillations of constant amplitude because the energy supplied each cycle exactly compensates for…

• A. High
• B. Audio
• C. Very low
• D. Very high

Explanation: Very low frequencies require impractically large inductance or capacitance values in an LC resonant circuit.

• A. LC tank circuit
• B. Biasing circuit
• C. Transistor
• D. None of the above

Explanation: The transistor is the active device that provides amplification and compensates for losses in the LC tank.

• A. Positive
• B. Negative
• C. Neither positive nor negative
• D. Data insufficient

Explanation: An oscillator uses positive feedback so that a portion of the output reinforces the input and sustains the oscillations.

• A. Two
• B. Three
• C. Four
• D. None of the above

Explanation: A transistor phase-shift oscillator normally uses three RC sections, which together provide 180° phase shift; the transistor supplies the…

• A. Radio receiver
• B. Radio transmitter
• C. AF sweep generator
• D. None of the above

Explanation: Crystal oscillators are commonly used in radio transmitters to generate a highly stable carrier frequency.

• A. 1
• B. 01
• C. 10
• D. 02

Explanation: For sustained oscillation, the Barkhausen magnitude condition is A_vβ = 1, so β = 1/A_v = 1/50 = 0.02.

• A. Phase-shift oscillator
• B. Hartely-oscillator
• C. Colpitt's oscillator
• D. Crystal oscillator

Explanation: A crystal oscillator uses the crystal's sharply defined mechanical resonance, so its frequency is essentially fixed and highly stable.

• A. Its low output
• B. Its high Q
• C. Less availability of quartz crystal
• D. Its high output

Explanation: A crystal oscillator generally produces relatively low output power because the crystal is a resonant element with limited mechanical…

• A. Less than 1
• B. More than 1
• C. Equal to 1
• D. None of the above

Explanation: The feedback fraction β is the fraction of the output voltage returned to the input, normally produced by a passive voltage-divider…

• A. 100
• B. 1000
• C. 50
• D. More than 10,000

Explanation: Quartz crystals have an exceptionally high Q, commonly of the order of tens of thousands or higher.

• A. Is increased
• B. Is reduced
• C. Remains the same
• D. None of the above

Explanation: Negative feedback opposes part of the input signal, reducing the closed-loop voltage gain according to Av = A/(1 + Aβ).

• A. Remains the same
• B. Decreases
• C. Increases
• D. Insufficient data

Explanation: For a balanced Wien bridge, the oscillation frequency is approximately f = 1/(2πRC).

• A. A gain of 1 around the feedback loop
• B. No gain around the feedback loop
• C. The attention of the feedback circuit must be one-third
• D. The feedback circuit must be capacitive

Explanation: The Barkhausen magnitude condition requires the loop gain Aβ to be unity for sustained oscillations, along with zero net phase shift.

• A. Has more gain
• B. Requires no input signal
• C. Requires no d.c. supply
• D. Always has the same input

Explanation: An amplifier needs an external input signal, whereas an oscillator generates its own periodic output from noise and circuit feedback.

• A. A voltage developed because of mechanical stress
• B. A change in resistance because of temperature
• C. A change in frequency because of temperature
• D. None of the above

Explanation: The piezoelectric effect produces an electric voltage when a crystal is mechanically stressed, and the reverse effect produces mechanical…

• A. High
• B. Very high
• C. Almost zero
• D. Low

Explanation: An emitter follower provides voltage-series feedback, which lowers its output impedance while giving a voltage gain close to unity.