A wire has a resistance of \( 35 \, \Omega \) at \( 20^\circ \text{C} \) and \( 36.4 \, \Omega \) at \( 60^\circ \text{C
**Resistivity temperature variation** ρ_t = ρ₀[1+α(T-T₀)], α ≈4×10⁻³ /°C for copper, 1.7×10⁻⁴ /°C for nichrome. Given R=60 Ω at 30°C, α=1.7×10⁻⁴ /°C, T=330°C, ΔT=300°C, R_t=60[1+1.7×10⁻⁴×300]=60×1.051=63.06 Ω, modest increase for nichrome due to small α. Use: R_t = R₀ [1 + α (T - T₀)] . Substitute: 36.4 = 35 [1 + α (60 - 20)] . Solve: 36.4 = 35 + 1400α ⇒ 1400α = 1.4 ⇒ α = (1.4/1400) = 1.0 × 10⁻³ °C⁻¹ . 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,
Ref: NCERT > Physics Book > Current Electricity > Temperature Dependence of Resistance and Resistivity