Question

The resistance of a wire is $4.2\Omega$ at ${100}^{\circ }C$ and the temperature coefficient of the material is $0.004{/}^{\circ }C$. Its resistance at $0^{\circ }C$ is

• A. $2.5\Omega$
• B. $3\Omega$
• C. $5\Omega$
• D. $6\Omega$

Answer 1

The correct option is B $3\Omega$

The effect of temperature on resistance is,

$R_t=R_0[1+\alpha t]$

Where, $R_0$-is resistance at $0^{\circ }C$

$R_0=\frac{R_t}{1+\alpha t}=\frac{4.2}{1+(0.004\times 100)}$

$\therefore R_0=\frac{4.2}{1.4}=3\Omega$

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}--> Hence, $\left(B\right)$ is the correct answer.