PhysicsCurrent Electricity

The deflection of galvanometer decreases from 25 divisions to 5 divis…

The deflection of galvanometer decreases from 25 divisions to 5 divisions when a resistor of 20Ω is connected in series. What is galvanometer resistance.

Answer & explanation

Correct answer: option 2

When resistor $20 Ω$ is not connected,
From Ohms law $V = I R,$ we get $V = 25 R_{G} . . . (1)$ where $R_{G} =$ resistance of galvanometer.
When resistor $20 Ω$ is connected,
$V = 5 (20 + R_{G}) . . . (2)$
Using Equation 1 and 2, $25 R_{G} = 5 (20 + R_{G})$
$\Rightarrow 5 R_{G} = 20 + R_{G}$
$\Rightarrow 4 R_{G} = 20$ $\Rightarrow R_{G} = 5 Ω$

The deflection of galvanometer decreases from 25 divisions to 5 divis…

When resistor 20Ω is not connected, From Ohms law V=IR, we get V=25RG​...(1) where RG​= resistance of galvanometer.When resistor 20Ω is connected,V = 5(20+RG​)...(2)Using Equation 1 and 2, 25RG​ = 5(20+RG​)⇒ 5RG ​= 20+RG​⇒ 4RG​ = 20 ⇒ RG​ = 5Ω

The deflection of galvanometer decreases from 25 divisions to 5 divis…

When resistor 20Ω is not connected, From Ohms law V=IR, we get V=25RG​...(1) where RG​= resistance of galvanometer.When resistor 20Ω is connected,V = 5(20+RG​)...(2)Using Equation 1 and 2, 25RG​ = 5(20+RG​)⇒ 5RG ​= 20+RG​⇒ 4RG​ = 20 ⇒ RG​ = 5Ω