# Electrical Measurements Questions and Answers – Limitations of Wheatstone Bridge

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Limitations of Wheatstone Bridge”.

1. Wheatstone bridge can’t be used for measurement of _________
a) high resistance
b) medium resistance
c) low resistance
d) accurate resistance

Explanation: Wheatstone bridge can be used for the measurement of medium resistances only. Kelvin bridge is used for the measurement of medium resistances.

2. Cost of maintenance of Wheatstone bridge is _________
a) low
b) high
c) depends on the components
d) depends on the source e.m.f

Explanation: As the resistance must have a tolerance of upto 1%, cost of maintenance of the Wheatstone bridge circuit is expensive. Voltage source does not add to the cost of maintenance of a Wheatstone bridge as it is uniform for all bridge circuits.

3. What is the effect of galvanometer on measurement of high resistance?
a) no effect
b) depends on the e.m.f source
c) galvanometer becomes insensitive to an imbalance
d) depends on the type of galvanometer used

Explanation: If the Wheatstone bridge is used for the measurement of high resistance, the galvanometer becomes insensitive and does not detect any imbalance.

4. What is the effect of heat on the resistances in a Wheatstone bridge?
a) no effect
b) increases the voltage drop across the circuit
c) decreases the current flowing through the circuit
d) causes a permanent change in the resistance values

Explanation: As the current flowing through the Wheatstone bridge circuit increases, the temperature of the resistance increases. As a result the resistance values are changed permanently.

5. Effect of high dc on Wheatstone bridge.
a) no effect
b) not susceptible
c) burns the circuit
d) increases the temperature

Explanation: A Wheatstone bridge is not susceptible to the flow of high dc current. A Wheatstone bridge in simplest form is used for the measurement of resistance with values in the medium resistance range.
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6. A Wheatstone bridge may not give accurate readings if _________
a) it is not balanced
b) it is balanced
c) the voltage drop across the circuit is maximum
d) excessive current flows through the circuit

Explanation: A Wheatstone bridge circuit may give inaccurate measurement of resistance if it is not balanced properly. Current flow through a Wheatstone bridge circuit is fixed as the e.m.f source magnitude is constant.

7. What is the effect of lead wires on the Wheatstone bridge?
a) no effect
b) stabilizes the system
c) desensitizes the system
d) increases the resistance of the circuit

Explanation: The lead wires connecting the resistance arms of a Wheatstone bridge add to the existing values of resistances across the ratio arms. As a result the net value of resistance changes, thus destabilizing the system.

8. Why a Wheatstone bridge can’t be used for signal conditioning?
a) due to the galvanometer
b) due to excessive current flow
c) due to the e.m.f source used
d) due to lead wires

Explanation: Lead wires add to the resistance of the arms of the Wheatstone bridge. As a result the bridge circuit is destabilized and can’t be used for signal conditioning.

9. How to minimize the drift in the value of resistance measured using a Wheatstone bridge?
a) by using a high precision null detector
b) by keeping the lead wire resistances within 0.2 mΩ
c) by using a e.m.f source of minimum value
d) by minimizing the flow of current

Explanation: The drift in the measured value of resistance in a Wheatstone bridge can be minimized by maintaining the lead wire resistances within 0.2 mΩ. As a result, the effect of lead wire resistance gets removed in the output value of the bridge circuit.

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