Current Electricity

As shown in the figure, the resistance of a galvanometer G can be found by the half-deflection method. Here the resistance R₂ is adjusted such that when the key K is closed the deflection in the galvanometer becomes half of the value as compared to when K is open. Half-deflection is obtained at R₂ = 4 $\Omega$ and thus the galvanometer resistance is found to be 6 $\Omega$. In this half-deflection condition the current (in mA) through the resistor R₁ is :