# Electrical Measurements Questions and Answers – Sensitivity of Wheatstone Bridge

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

1. When the bridge is balanced, what is the current flowing through the galvanometer?
a) 0
b) depends on the ratio arms R1 and R2
c) varies by a factor of 2
d) depends on the type of null detector used

Explanation: Under bridge balance condition, no current flows through the galvanometer. Current flow is independent of the values of ratio arms R1 and R2.

2. Amount of deflection of the galvanometer depends on _________
a) resistance of the ratio arms
b) sensitivity
c) current flowing through the bridge
d) emf across the circuit

Explanation: The amount of deflection of the galvanometer depends upon its sensitivity. Resistance of the ratio arms does not affect the amount of deflection of the galvanometer.

3. Sensitivity is defined as _________
a) amount of voltage per unit current
b) amount of power per unit voltage
c) amount of resistance per unit voltage
d) amount of deflection per unit current

Explanation: Sensitivity is expressed as

Thus sensitivity is defined as the amount of deflection per unit current.

4. Sensitivity is expressed in _________
a) cm/A
b) m/mA
c) mm/µA
d) inch/nA

Explanation:

where, deflection is in mm and current is in µA.
So the unit of sensitivity is mm/ µA.

5. What is the relation between the sensitivity and deflection for a galvanometer?
a) directly proportional
b) inversely proportional
c) independant of each other
d) depends on the type of galvanometer used

Explanation:

Thus we see that sensitivity is directly proportional to the deflection.
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6. The voltage sensitivity of a galvanometer is given by _________
a) Sv = eθ
b) Sv = θe
c) Sv = 1e
d) Sv = 1θ

Explanation:

Voltage sensitivity is defined as the amount of deflection per unit voltage and is given by the relation
Sv = θe.

7. Unit of voltage sensitivity is _________
a) volts per degrees
b) amps per ohms
c) degrees per volts
d) watts per amps

Explanation:

So the unit of voltage sensitivity is degrees per volts as deflection is measured in degrees and voltage is in volts.

8. Bridge sensitivity is defined as _________
a) $$S_B=\frac{\theta}{R}$$
b) $$S_B=\frac{\theta}{\Delta R}$$
c) $$S_B=\frac{1}{\frac{\Delta R}{R}}$$
d) $$S_B=\frac{\theta}{\frac{\Delta R}{R}}$$

Explanation: The bridge sensitivity is defined as the amount of deflection of the galvanometer per unit fractional change in the unknown resistance.
$$S_B=\frac{\theta}{\frac{\Delta R}{R}}$$
Here ∆R/R denotes the fractional change in the unknown resistance.

9. Maximum sensitivity occurs when?
a) R3R4 = 1
b) R2R4 = 1
c) R1R2 = 1
d) R3R2 = 1

Explanation: Under a small unbalance condition, the bridge sensitivity equation becomes

Here E is the emf of the circuit. For maximum bridge sensitivity, we get R3=R4.

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