# Measurements

### Explanation of question 1

List I contains the three essential features of an analogue indicating instrument. List II contains their function.

List I | List II
A | Deflecting device | 1 | To give a deflection dependent upon the magnitude of the quantity being measured
B | Controlling device | 2 | To convert the quantity being measured into a mechanical force
C | Damping device | 3 | To prevent oscillation of the moving system

The correct match between the two lists is

1. A1, B2, C3
2. A2, B1, C3
3. A2, B3, C1
4. A3, B1, C2

The answer is :- 2 It is easy to confuse A and B in list I. The function of a deflecting device is to convert that quantity to be measured into a mechanical force. The controlling device (normally spring or gravity) is to control the deflection so that its value is dependent upon the size or magnitude of that quantity being measured. The inertia of the moving system and the controlling torque will impart a natural frequency of oscillation to the pointer. The damping device (commonly eddy-current or air) is to suppress oscillation.

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