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Science · 2022 · 2 marks
CBSE 2022 · Region 3 · Set 1 · Q4
An electric heater rated $\displaystyle 1100$ W operates at $\displaystyle 220$ V. Calculate(i)its resistance, and (ii) the current drawn by it.Calculate the equivalent resistance of the following electric circuit:
An electric heater rated $\displaystyle 1100$ W operates at $\displaystyle 220$ V. Calculate
(i)
its resistance, and (ii) the current drawn by it.
Calculate the equivalent resistance of the following electric circuit:
Marking-scheme solution
$\displaystyle P($ Power $\displaystyle )=V($ Potential difference $\displaystyle ) \times I($ Current $\displaystyle )$
Here $\displaystyle P=1100 \mathrm{~W}, V=220 \mathrm{~V}, I=?, R=$ ?
\[P=\frac{V^{2}}{R}
\]
(i)
$\displaystyle R=\frac{\mathrm{V}^{2}}{\mathrm{P}}$
\[\begin{array}{l}
=\frac{22 \varnothing \mathrm{~V} \times 22 \varnothing \mathrm{~V}}{11 \varnothing \varnothing \mathrm{~W}} \\
=44 \Omega
\end{array}
\]
(ii)
$\displaystyle I=\frac{V}{R}$
\[I(\text { Current })=\frac{V}{R}=\frac{220 \mathrm{~V}}{44 \Omega}=5 \mathrm{~A}
\]
\[\begin{array}{l}
R_{S}=R_{3}+R_{4}=10+10=20 \Omega \\
\frac{1}{R_{P}}=\frac{1}{R_{2}}+\frac{1}{R_{S}} \\
\quad=\frac{1}{20}+\frac{1}{20}=\frac{1}{10} \Omega \\
R_{P}=10 \Omega
\end{array}
\]
Total equivalent resistance $\displaystyle =R=R_{1}+R_{P}+R_{5}$
\[=R=20+10+10=40 \Omega
\]
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CBSE Class 10 Science past-paper question from the 2022board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.