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Physics · 2026 · 2 marks
CBSE 2026 · Region 2 · Set 1 · Q20
A heating element using nichrome is connected to a 220 V supply. Initially it draws a current of 2.9 A. After some time, the current attains a steady…
A heating element using nichrome is connected to a $\displaystyle 220$ V supply. Initially it draws a current of $\displaystyle 2.9$ A. After some time, the current attains a steady value of $\displaystyle 2.5$ A. Find the steady temperature of the heating element if the room temperature is $\displaystyle 27$ °C. The temperature coefficient of resistance of nichrome is $\displaystyle 1.7 \times 10^{-4}{ }^{\circ} \mathrm{C}^{-1}$.
Marking-scheme solution
$\displaystyle \mathrm{R}_{1}=\dfrac{\mathrm{V}}{\mathrm{I}_{1}}=\dfrac{220}{2.9}\ \Omega$ at temperature $\displaystyle t_{1}$
$\displaystyle \mathrm{R}_{2}=\dfrac{\mathrm{V}}{\mathrm{I}_{2}}=\dfrac{220}{2.5}\ \Omega$ at temperature $\displaystyle t_{2}$
$\displaystyle \mathrm{R}_{2}=\mathrm{R}_{1}\left[1+\alpha\left(t_{2}-t_{1}\right)\right]$
$\displaystyle t_{2}-t_{1}=\dfrac{\mathrm{R}_{2}-\mathrm{R}_{1}}{\mathrm{R}_{1} \alpha}$
$\displaystyle t_{2}-27=\dfrac{\left(\dfrac{220}{2.5}-\dfrac{220}{2.9}\right)}{\left(\dfrac{220}{2.9} \times 1.7 \times 10^{-4}\right)}$
$\displaystyle t_{2} \approx 968^{\circ} \mathrm{C}$
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CBSE Class 12 Physics past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.