Question

A flash light lamp is marked $3.5V$ and $0.28A.$ The filament temperature is ${425}^{0}C.$ The filament resistance at $0^{0}C$ is $4\Omega .$ then$,$ the temperature coefficient resistance of the material of the filament is

• A. $8.5\times {10}^{-3}/K$
• B. $3.5\times {10}^{-3}/K$
• C. $0.5\times {10}^{-3}/K$
• D. $5\times {10}^{-3}/K$

Answer 1

The correct option is D $5\times {10}^{-3}/K$

$\alpha =\frac{R_2-R_1}{R_1{t}_2-R_2{t}_1}=\frac{12.5-4}{4\left(425\right)-12.5\left(0\right)}=5\times {10}^{-3}/k$