CBSE 2026 · Region 2 · Set 1 · Q20 · 2 marks
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 $\displaystyle t_{2}$
$\displaystyle \mathrm{R}_{2}=\mathrm{R}_{1}\left[1+\alpha\left(t_{2}-t_{1}\right)\right]$
$\displaystyle t_{2}-t_{1}=\dfrac{\mathrm{R}_{2}-\mathrm{R}_{1}}{\mathrm{R}_{1} \alpha}$
$\displaystyle t_{2}-27=\dfrac{\left(\dfrac{220}{2.5}-\dfrac{220}{2.9}\right)}{\left(\dfrac{220}{2.9} \times 1.7 \times 10^{-4}\right)}$
$\displaystyle t_{2} \approx 968^{\circ} \mathrm{C}$
Current ElectricityTemperature Dependence of ResistivityApplyvery_short_answermedium
More from Current Electricity
- A steady current flows through a metallic wire whose area of cross-section increases continuously from one…2023 · asked 3×
- (i) Define mobility of electrons. Give its SI units. (ii) A steady current flows through a wire AB, as shown…2023 · asked 3×
- What is the order of magnitude of drift velocity of electrons in a conductor? Deduce the relation between the…2026 · asked 3×
- A student sets up the circuit as shown in the figure to find the value of unknown resistance X and records a…2026 · asked 3×
- What is meant by 'relaxation time' of free electrons in a conductor? Show that the resistance of a conductor…2024 · asked 3×
- Two batteries of emf's 3 V \& 6 V and internal resistances 0.2 Ω & 0.4 Ω are connected in parallel. This…2025 · asked 3×
- Four resistors, each of resistance R and a key K are connected as shown in the figure. The equivalent…2025 · asked 3×
- An electric iron rated 2‧2 kW, 220V is operated at 110 V supply. Find: (i) its resistance, and (ii) heat…2026 · asked 3×
CBSE Class 12 Physics past-paper question from the 2026board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.