Two cells of emf \( 3 \, \text{V} \) and \( 6 \, \text{V} \) with internal resistances \( 1 \, \Omega \) and \( 2 \, \Om
**Conductivity** σ=1/ρ decreases with temperature for metals, σ = n e² τ/m, τ ∝1/T due to lattice vibrations. For semiconductors, n increases exponentially with T, so σ increases, opposite to metals, explaining why metallic resistance rises with temperature. For series: εₑq = ε₁ + ε₂ = 3 + 6 = 9 V . 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 9.0 V,
Ref: NCERT > Physics Book > Current Electricity > Temperature Dependence of Resistance and Resistivity
