Electromagnetism

For zero galvanometer deflection, the bridge must be balanced. This is a Wheatstone bridge arrangement.

The condition for a balanced Wheatstone bridge is:

Where R₁, R₂, R₃, and R₄ represent the resistance in each arm of the Wheatstone bridge. Here, R₁ and R₂ are the resistances of the wire segments AJ and JB respectively, and R₃ = 8 Ω and R₄ = 12 Ω.

The length of AB is 40 cm, thus,

3x = 80 − 2x 5x = 80 x = 16 cm

Distance of J from B = 40 cm − 16 cm = 24 cm