The deflection in moving coil Galvanometer is reduced to half when it is shunted with a \(40 \Omega\) coil. The resistance of the Galvanometer is (c) \(40 \Omega\) (a) \(60 \Omega\) (b) \(\overline{10 \Omega}\) (d) \(20 \Omega\)

Short Answer

Expert verified
The resistance of the galvanometer is \(20\Omega\). The correct answer is (d) \(20\Omega\).

Step by step solution

01

Understand the concept of shunt resistance and total resistance

A shunt is a low resistance connected in parallel with a high resistance. In this case, the 40Ω coil is the shunt resistance, and it is connected in parallel with the galvanometer resistance (which we need to find). The total resistance for two resistances in parallel is given by the formula: \[ \frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2} \]
02

Apply current division formula to find the proportion of current

It is given that the deflection in the moving coil galvanometer is reduced to half when it is shunted with a 40Ω coil, which means the current, when the galvanometer is shunted, is half of the original current. For two resistances in parallel, the current is divided inversely proportionally to the resistance values: \[ \frac{I_1}{I_2} = \frac{R_2}{R_1} \] Since the deflection in the galvanometer is reduced to half, we can write the equation as: \[ \frac{I}{\frac{1}{2}I} = \frac{R_{shunt}}{R_{galv}} \] Where \(R_{shunt} = 40\Omega\) is the shunt resistance and \(R_{galv}\) is the resistance of the galvanometer.
03

Solve for the resistance of the galvanometer

Simplify the proportion equation to find the value of \(R_{galv}\) \[\frac{1}{\frac{1}{2}} = \frac{40\Omega}{R_{galv}}\] \[2 = \frac{40\Omega}{R_{galv}}\] Now, we can solve for \(R_{galv}\): \[ R_{galv} = \frac{40\Omega}{2} \] \[ R_{galv} = 20\Omega \] The resistance of the galvanometer is \(20\Omega\). The correct answer is (d) \(20\Omega\).

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