A flash light lamp is marked 3.5 V and 0.28 A .  The filament temperature is 4250C. The filament resistance at 00C is 4Ω . Then, the temperature coefficient of resistance of the material of the filament is

Potential difference V=3.5 V Current i=0.28 A Temperature t=4250 c Resistance at 0o c (R0) =4 Ω Temperature coefficient of resistance α=? Rt=Vi=3.50.28=12.5Ω ∝ =Rt−R0R0t  ⇒12.5−44×425   ⇒8.54×425⇒0.024    ⇒5×10−3/K .