# Electrical Measurements Questions and Answers – Operation of Strain Gauges

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Operation of Strain Gauges”.

1. Electrical strain gauge works on the principle of __________
a) variation of resistance
b) variation of capacitance
c) variation of inductance
d) variation of area

Explanation: An electrical strain gauge works on the basis of change in resistance as a function of strain. The wire resistance increases with tension and reduces with compression.

2. The strain gauge is not bonded to the specimen.
a) True
b) False

Explanation: The gauge is under the same strain as that the specimen under test. As a result the strain gauge is bonded to the specimen.

3. Bonding element in a strain gauge must have __________
a) zero insulation resistance
b) low insulation resistance
c) high insulation resistance
d) infinite insulation resistance

Explanation: In a strain gauge, the bonding element must have a high value of insulation resistance. It should be immune to effects of moisture and must also have the ability to transmit strain.

4. Dynamic strain measurements use __________
a) brass iron alloy
b) iron aluminium alloy
d) nickel chromium alloy

Explanation: Nickel chromium alloy is also known as a nichrome alloy. It contains 80 % of Nickel and 20 % of Chromium. Platinum is used for the temperature compensation of nickel chromium alloys.

5. Commonly used elements for wire strain gauges are __________
a) nickel and copper
b) nickel and gold
c) gold and brass
d) silver and aluminium

Explanation: Nickel and copper are the most commonly used elements for wire strain gauges. They comprise of 45 % of Nickel and 55 % of Copper. They exhibit a high value of specific resistance.

6. Cement is classified under __________
a) 4 types
b) 2 types
c) 6 types
d) 8 types

Explanation: Cement can be divided into two broad categories. They are as follows:
i) Solvent setting cement
ii) Chemically reacting cement.

7. Proper functioning of a strain gauge depends on __________
a) strain
b) stress
c) bonding
d) length of wire

Explanation: A strain gauge works properly only if the bonding material used is durable and keeps the gauge together to the surface of the material that is being tested.

8. Gauge factor is given by which of the following relation?
a) S = $$\frac{\Delta R/R}{\Delta l}$$
b) S = $$\frac{\Delta R}{\Delta l/l}$$
c) S = $$\frac{R}{\Delta l/l}$$
d) S = $$\frac{\Delta R/R}{\Delta l/l}$$

Explanation: Gauge factor in a strain gauge is given by the relation
S = $$\frac{\Delta R/R}{\Delta l/l}$$
where, S is the gauge factor
R is the gauge wire resistance
∆R is the change in resistance
l is the length of the wire in unstressed condition
∆l is the change in length of the wire.

9. Poisson’s ratio is given by which of the following relation?
a) µ = –$$\frac{\Delta d/d}{\Delta l/l}$$
b) µ = –$$\frac{\Delta d}{\Delta l/l}$$
c) µ = –$$\frac{d}{\Delta l/l}$$
d) µ = –$$\frac{\Delta d/d}{\Delta l}$$

Explanation: Poisson’s ratio is given by the relation
µ = –$$\frac{\Delta d/d}{\Delta l/l}$$
where, d is the diameter of the cross-section of the wire
∆d is the change in the diameter of cross-section of the wire.

10. Proper bonding causes errors in strain gauges.
a) True
b) False