JEE Main 2016 · 9 Apr · Shift 1 · Physics Q16

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A 50 Ω resistance is connected to a battery of 5 V. A galvanometer of resistance 100 Ω is to be used as an ammeter to measure current through the resistance, for this a resistance $r_s$ is connected to the galvanometer. Which of the following connections should be employed if the measured current is within 1% of the current without the ammeter in the circuit ?

r_s=0.5

Ω in parallel with the galvanometer

r_s=0.5

Ω in series with the galvanometer

r_s=1

Ω in series with galvanometer

r_s=1

Ω in parallel with galvanometer

Answer and worked solution

Official answer: A

For the reading to be within 1%, the ammeter must add at most 0.5 Ω to the 50 Ω circuit. A 0.5 Ω shunt in parallel gives $\frac{0.5\times100}{100.5}\approx0.4975$ Ω, which qualifies; a 1 Ω shunt gives about 0.99 Ω (2% error).

Topics:Ammeters and voltmeters Moving coil galvanometer

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JEE Main 2016 · 9 Apr · Shift 1, Physics question 16