# Electronic Devices and Circuits Questions and Answers – The Rectifier Voltmeter

This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “The Rectifier Voltmeter”.

1. _________ diodes are preferred in AC rectifier voltmeter arrangements.
a) Silicon
b) Germanium
c) Gallium
d) Arsenide

Explanation: Silicon diodes are preferred because of their low reverse current and high forward current ratings. A PMMC movement is also used by the rectifier type instruments along with a rectifier arrangement.

2. AC voltmeter consists of_________
a) half wave rectifier
b) full wave rectifier
c) center tap rectifier
d) bridge wave rectifier

Explanation: The bridge rectifier provides a full wave pulsating dc. Due to the inertia of the movable coil, the meter indicates a steady deflection proportional to the average value of the current. The meter scale is usually calibrated to give the RMS value an alternating sine wave input.

3. In reverse bias, rectifier behaves as a___________
a) Resistor
b) Capacitor
c) Inductor
d) Amplifier

Explanation: The rectifier exhibits capacitance properties when reverse biased, and tends to bypass higher frequencies. The meter reading may be in error by as much as 0.5% decrease for every 1 kHz rise in frequency.

4. In a general rectifier voltmeter, the meter has low sensitivity because of ___________ of the diode.
a) low forward resistance
b) high forward resistance
c) low reverse impedance
d) high reverse impedance

Explanation: The diode offers high resistance when forward biased. Thus, offering more resistance to the current flow in the circuit. Thus making the meter less sensitive.

5. Which of the following instruments cannot be applied for ac measurements?
a) Hot wire
b) PMMC
c) Electrostatic
d) Induction type

Explanation: The moving coil instrument can only be used on D.C supply as the reversal of current produces a reversal of torque on the coil. It’s very delicate and sometimes uses AC circuit with a rectifier. It’s costly as compared to moving coil iron instruments.
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6. The resistance of an ideal voltmeter is __________
a) low
b) infinite
c) zero
d) high

Explanation: The internal resistance of an ideal voltmeter is infinity and the internal resistance of an ideal ammeter is zero. Ammeter is connected in series and voltmeter is connected in parallel with the electric appliance. The resistance of an idea voltmeter is infinite so that it draws no current from the circuit under test.

7. Electronic voltmeters can be designed to measure ____________
a) Only very small voltages
b) Only very high voltages
c) Both very small and very high voltages
d) Neither high nor small voltages

Explanation: A voltmeter is an instrument that measures the difference in electrical potential between two points in an electric circuit. An analog voltmeter moves a pointer across a scale in proportion to the circuit’s voltage; a digital voltmeter provides a numerical display. Thus it is suitable for measuring both small and high voltages.

8. In electronic voltmeter, the range of input voltages can be extended by using _______
a) Functional switch
b) Input attenuator
c) Rectifier
d) Balanced bridge dc amplifier

Explanation: The function of the attenuator is that it helps to select a particular range of voltage values. The rectifier is essential in a voltmeter for the conversion of AC voltage into DC voltage.

9. The scale of a voltmeter is uniform. Its type is _________
a) Moving Iron
b) Induction
c) Moving coil permanent magnet
d) Moving coil dynamometer

Explanation: Moving coil permanent magnet instruments have permanent magnets. It is suited for DC measurement because here deflection is proportional to the voltage because resistance is constant for a material of the meter and hence if voltage polarity is reversed, deflection of the pointer will also be reversed so it is used only for DC measurement.

10. Which of the instruments is most accurate?
a) PMMC
b) Moving iron
c) Thermo couple
d) Induction type

Explanation: This torque in PMMC ensures the pointer comes to an equilibrium position i.e. at rest in the scale without oscillating to give an accurate reading. In PMMC as the coil moves in the magnetic field, eddy current sets up in a metal former or core on which the coil is wound or in the circuit of the coil itself which opposes the motion of the coil resulting in the slow swing of a pointer and then come to rest quickly with very little oscillation. It has great accuracy.

Sanfoundry Global Education & Learning Series – Electronic Devices and Circuits.

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