JEE Main · 2016 · 03 Apr 2016 · Offline · Current Electricity

A galvanometer having a coil resistance of

100Ω

gives a full scale deflection, when a current of 1 mA is passed through it. The value of the resistance, which can convert this galvanometer into ammeter giving a full scale deflection for a current of 10 A is :

(A) $2Ω$
(B) $0.1Ω$
(C) $3Ω$
(D) $0.01Ω$ ✓ Correct

Answer: (D)

Solution

To read large currents a galvanometer is shunted by a small resistance

S

in parallel, chosen so that at full scale the voltage across the coil equals the voltage across the shunt:

i_{g} G = (i - i_{g}) S

. With

G = 100 Ω

i_{g} = 1

mA and full-scale line current

i = 10

S = \frac{i _{g} G}{i - i _{g}} = \frac{1 0 ^{- 3} \times 100}{10 - 1 0 ^{- 3}} \approx \frac{0.1}{10} = 0.01 Ω

JEE Main · 2016 · 03 Apr 2016 · Offline · Single correct option

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