# Potentiometers MCQ || Measurement and Instrumentation Potentiometer Questions and Answers

1. The Potentiometer is generally used to measure _______

1. Velocity
2. Speed
3. Displacement
4. Power

Explanation:

A potentiometer is a resistive type transducer. It is generally used to measure linear or angular displacement. The resistive transducer is those in which the resistance change due to a change in some physical phenomenon.

The change in the value of resistance with a change in the length of the conductor can be used to measure displacement.

To measure displacement, a potentiometer is typically wired as a ‘voltage divider’ so that the output voltage is proportional to the distance traveled by the wiper.

2. What should be the size of the slide wire of the potentiometer to make it achieve high accuracy?

1. As long as possible
2. As short as possible
3. 1 meter
4. Neither too thin nor too thick

Explanation:

potentiometer is defined as a 3 terminal variable resistor in which the resistance is manually varied to control the flow of electric current.

• A potentiometer acts as an adjustable voltage divider
• A potentiometer is a passive electronic component
• Potentiometers work by varying the position of a sliding contact across a uniform resistance

The slide wire of the potentiometer to make it achieve high accuracy should be as long as possible.

3. Standardization of potentiometer is used for _________

1. Accuracy
2. Precision in measurement
3. Use of low voltage sources
4. None of the mentioned

Explanation:

Standardization of a potentiometer is a process of adjusting the working current supplied by the supply battery such that the voltage drop across a portion of sliding wire matches with the Standard reference source.

The purpose of standardization is to develop a known potential difference across the unit length of the potentiometer wire. This is achieved by balancing the known e.m.f. of a standard cell across the known length of the potentiometer wire.

In order to get this condition, we adjust the current flowing in the potentiometer wire with the help of the rheostat connected to the circuit.

Standardization of potentiometer is done in order that they become accurate and give a direct reading.

4. Basically a potentiometer is a device for

1. Comparing two voltages
2. Measuring a current
3. Comparing two currents
4. Measuring a voltage

Explanation:

• The instrument that is designed to measure the unknown voltage by comparing it with the known voltage is called a potentiometer.
• In the potentiometer, for comparison, the known voltage is used by a standard cell or any other known voltage reference source by using wire.
• It makes use of a balance or null condition, no current flows, and hence no power loss is consumed in the circuit
• Measurements by such comparison methods give results of a high degree of accuracy because the result obtained does not depend upon the actual deflection of the pointer.

5. Which of the following device is used for calibration of a potentiometer?

1. Variable dc source
2. Galvanometer
3. Electrochemical cell
4. All of the mentioned

Explanation:

• The instrument that is designed to measure the unknown voltage by comparing it with the known voltage is called a potentiometer.
• In the potentiometer, for comparison, the known voltage is used by a standard cell or any other known voltage reference source by using wire.
• A standard electrochemical cell is used of known emf.
• The supply voltage is adjusted until the galvanometer indicates zero reading, then the voltage is measured across the resistor which is equal to the standard cell voltage.

6. A potentiometer work on

1. Heating effect
2. Magnetic effect
3. Electromagnetic induction
4. Fall of potential

Explanation:

The basic working principle of the Potentiometer is based on the fact that the fall of the potential across any portion of the wire is directly proportional to the length of the wire, provided the wire has a uniform cross-sectional area and the constant current flowing through it.

The working of the potentiometer is the same as that of a variable resistor. The construction is also the same. A rheostat is also a variable resistor and is a 2-terminal device. It is commonly used for handling higher currents and voltages.

7. Which of the following can be measured using a potentiometer?

1. DC voltage
2. Temperature
3. Displacement
4. All of the above

Explanation:

The potentiometer can measure different quantities like DC voltage, resistance, and temperature.

Resistance Measurement: Potentiometers are especially suited for comparing a low resistance with a standard resistance of the same order. The ratio of unknown resistance to the resistance of the standard is the same as the ratio of the voltage drop across the two resistances as measured by the potentiometer.

Temperature Measurement: For the measurement of temperature using the potentiometer thermocouples are used. In thermocouples, two different metals are placed in contact and there exists a potential difference between them.

Self Reactance Measurement: An a.c potentiometer can be used for the measurement of self-reactance of a coil by connecting a standard resistance in series with the coil.

Displacement Measurement: A potentiometer is a resistive type transducer. It is generally used to measure linear or angular displacement. The change in the value of resistance with a change in the length of the conductor can be used to measure displacement.

8. A simple slide wire potentiometer is used for the measurement of current in a circuit. The voltage drop across a standard resistor of 0.1 Ω is balanced at 75 cm. Find the magnitude of current if the standard cell emf 1.45 volt is balanced at 50 cm.

1. 40 A
2. 35 A
3. 15.5 A
4. 21.75 A

Explanation:

The standard cell emf 1.45 volt is balanced at 50 cm

The voltage drop per unit length = 1.45/50 = 29 mV/cm

The voltage drop across a standard resistor of 0.1 Ω is balanced at 75 cm

The voltage drop across 75 cm length = 29 × 10-3 × 75 = 2.175 V

The resistance of 75 cm length wire = 0.1 Ω

Current through the circuit = 2.175/0.1 = 21.75 A

9. Which of the following devices is used in the potentiometer as calibrating device?

1. Wattmeter
2. Ammeter
3. Voltmeter
4. All of the above

Explanation:

The potentiometer method is the basis for calibration of all voltmeters, ammeters, and wattmeters.

The ammeter to be calibrated is connected in series with a shunt of suitable resistance value and current-carrying capacity and the voltage drop across the shunt is measured by the potentiometer. The accuracy of current measurement in this method is very high since both the resistance of the shunt and the voltage drop across it can be determined very accurately.

10. A DC potentiometer uses a slide wire of 800 mm. A standard cell of emf 1.18 V obtains balance at 600 mm. A test cell is seen to obtain balance at 660 mm. The emf of the test cell is

1. 1.00 V
2. 1.30 V
3. 1.50 V
4. 1.70 V

Explanation:

Given-

E1 = 1.18 V

1 = 600 mm

L= 660 mm

In a potentiometer

L  R

Where,

E = emf of test cell

L = Balancing length of slide wire

R = Slide wire resistance

∴ E1/E2 = L1/L2

1.18/E2 = 600/660

E2 = 1.30 V

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