To measure the internal resistance r₁ of a cell of emf E, a metre bridge of wire resistance R₀ = 50 Ω, a resistance R₀/2, another cell of emf E/2 (internal resistance r) and a galvanometer are connected as shown. If the null point is at ℓ = 72 cm, find r₁ in ohms.

Question

G1 Physics · Accepted Answer

Apply the metre-bridge balance equation to the two sections of the 50 Ω bridge wire, including the R₀/2 branch and source internal resistance. With ℓ=72 cm the equation gives r₁=3 Ω.