JEE Main · 2019 · 09 Apr 2019 · Shift 2 · Current Electricity

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The resistance of a galvanometer is 50 ohm and the maximum current which can be passed through it is 0.002 A. What resistance must be connected to it in order to convert it into an ammeter of range

0 - 0.5 A

(A)0.2 ohm✓ Correct
(B)0.002 ohm
(C)0.02 ohm
(D)0.5 ohm

Answer: (A)

Solution

To read currents up to

0.5

A the galvanometer, which deflects fully at only

0.002

A, must be given a low-resistance shunt in parallel so the extra current bypasses the coil. The coil and shunt share the same voltage, so

I_{g} R_{g} = (I - I_{g}) S

, that is

0.002 \times 50 = (0.5 - 0.002) S

. Then

0.1 = 0.498 S

, giving

S \approx 0.2 Ω

JEE Main · 2019 · 09 Apr 2019 · Shift 2 · Single correct option

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