Practice question

**Meter bridge** uses uniform wire of length 1 m, balance length l gives R_unknown = R_known·l/(100-l). Principle same as Wheatstone, with wire resistances proportional to lengths, allowing unknown resistance determination from length ratio. Balance condition: (R₁/R₂) = (R₃/R₄) . Substitute: (12/24) = (18/R₄) . Solve: 0.5 = (18/R₄) ⇒ R₄ = (18/0.5) = 36 Ω . Applying I = n e A v_d, R = ρ l/A, R_t = R₀[1+αΔT], Kirchhoff's ΣI=0, ΣV=0, R_eq series/parallel, V = ε - I r and P = I²R, evaluation yields 36 Ω,