First slide

Moving coil Galvanometer

Question

A galvanometer, having a resistance of 50 $Ω$ , gives a full sale deflection for a current of 0.05 A. The length in metre of a resistance wire of area of cross-section 2.97x 10^-6 cm² that can be used to convert the galvanometer into an ammeter which can read a maximum of 5 A current is (specific resistance of the wire = 5 x 10^-7 $Ω$ m)

Moderate

A

8
B

6
C

3
D

1.5

Solution

Here $i = (\frac{G + S}{S}) i_{g}$
or $5 = (\frac{50 + R}{R}) \times 0 \cdot 05$
$∴ R = (50 / 99)$
Now, $R = \frac{ρl}{A} or l = \frac{RA}{ρ}$
$∴ l = \frac{(50 / 99) \times (2 .97 \times 10^{- 6})}{(5 \times 10^{- 7})} = 3 m$

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