JEE Main 2026 — Jan 24, Shift 2 — Physics solution

JEE Main2026Jan 24, Shift 2Physics

A moving coil galvanometer of resistance $100 Ω$ shows a full scale deflection for a current of $1$ mA. The value of resistance required to convert this galvanometer into an ammeter, showing full scale deflection for a current of $5$ mA, is _____ $Ω$ .

A
25
B
10
C
0.5
D
2.5

Solution

A shunt resistance $r_{s}$ in parallel with the galvanometer carries the excess current. At full deflection, $i_{g} = 1$ mA flows through the galvanometer and $(i - i_{g}) = 4$ mA flows through the shunt at the same voltage drop.

$i_{g} \cdot G = (i - i_{g}) \cdot r_{s} \Rightarrow r_{s} = \frac{G}{( i / i _{g} ) - 1} = \frac{100}{5 - 1} = 25 Ω$ .

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