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Physics · 2026 · 2 marks
CBSE 2026 · Region 5 · Set 1 · Q17
(a) An electric iron rated 2‧2 kW, 220V is operated at 110 V supply. Find: (i) its resistance, and (ii) heat produced by it in 10 minutes.
(a)
An electric iron rated $\displaystyle 2$‧$\displaystyle 2$ kW, 220V is operated at $\displaystyle 110$ V supply. Find :
(i)
its resistance, and
(ii)
heat produced by it in $\displaystyle 10$ minutes.
OR
(b)
A current of $\displaystyle 4$‧$\displaystyle 0$ A flows through a wire of length $\displaystyle 1$ m and cross-sectional area $\displaystyle 1.0 \mathrm{~mm}^{2}$, when potential difference of $\displaystyle 2$ V is applied across its ends. Calculate the resistivity of the material of the wire.
Marking-scheme solution
(i)
$\displaystyle \mathrm{R}=\dfrac{\mathrm{V}^{2}}{\mathrm{P}}$
$\displaystyle =\dfrac{(220)^{2}}{2.2 \times 10^{3}}=22\ \Omega$
(ii)
$\displaystyle \mathrm{H}=\mathrm{I}^{2} \mathrm{R}\, t$
$\displaystyle \mathrm{I}=\dfrac{\mathrm{V}_{\text {applied }}}{\mathrm{R}}=\dfrac{110}{22}=5 \mathrm{~A}$
$\displaystyle =5 \times 5 \times 22 \times 600$
$\displaystyle =3.3 \times 10^{5} \mathrm{~J}$
$\displaystyle \rho=\dfrac{RA}{l}$
$\displaystyle R=\dfrac{V}{I}=\dfrac{2}{4}=\dfrac{1}{2}\ \Omega$
$\displaystyle \rho=\dfrac{1 \times 10^{-6}}{2 \times 1}$
$\displaystyle =5 \times 10^{-7}\ \Omega \mathrm{~m}$
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