Measurement of Angle of Deflection

There are two methods to determine the angle of deflection of coil.

i) Lamp & Scale Arrangement

In a sensitive galvanometer, the angle of deflection is observed/measured by means of small mirror attached/connected to the coil along with lamp, as shown in diagram/figure. A beam of light from the lamp falls/drop on mirror of galvanometer. After reflection from mirror it produces/bring out a spot on a transparent scale placed at a distance of one meter (1m) from the galvanometer. When the coil rotates, the mirror attached to the coil also rotates (turn round) and spot of light moves (proceed) along the scale. The displacement of the spot of light on the scale is proportional to the angle of deflection (diverganca) (Spot of light ∝ angle of deflection), provided the angle of deflection is small.

ii) Pivoted Galvanometer

In this, the coil is pivoted among (b/w) two jewelled bearings. The restoring torque is provided (given) by two hair springs which also act (provide a role) as current leads. An aluminium pointer is joined/attached to the coil which moves over a scale, as shown in diagram. Such galvanometer is called Western-type Galvanometer.

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