CBSE 2025 · Region 5 · Set 1 · Q25 · 2 marks
(A)State two applications of Joule's heating in domestic electric circuit.(B)Establish the relationship between the commercial unit of electric energy and the SI unit of electric energy.Determine the total resistance of the parallel combination of three resistances of $\displaystyle 2 \Omega, 4 \Omega$ and $\displaystyle 6 \Omega$.
(A)
State two applications of Joule's heating in domestic electric circuit.
(B)
Establish the relationship between the commercial unit of electric energy and the SI unit of electric energy.
Determine the total resistance of the parallel combination of three resistances of $\displaystyle 2 \Omega, 4 \Omega$ and $\displaystyle 6 \Omega$.
Marking-scheme solution
(A)
Electric bulb / electric iron / Electric fuse / Electric heater / electric Oven
(a)
$\displaystyle 1$ \(\displaystyle \mathrm{kWh}=1000\) watt \(\displaystyle \times 3600\) second
\[\begin{aligned}
& =3.6 \times 10^{6} \text { watt second } \\
& =3.6 \times 10^{6} \text { Joule }(\mathrm{J})
\end{aligned}
\]
\[\begin{aligned}
& \frac{1}{\mathrm{R}_{\mathrm{p}}}=\frac{1}{\mathrm{R}_{1}}+\frac{1}{\mathrm{R}_{2}}+\frac{1}{\mathrm{R}_{3}} \\
& \frac{1}{\mathrm{R}_{\mathrm{p}}}=\frac{1}{2 \Omega}+\frac{1}{4 \Omega}+\frac{1}{6 \Omega} \\
& \therefore \mathrm{R}_{\mathrm{p}}=\frac{12}{11} \Omega=1 \cdot 09 \Omega
\end{aligned}
\]
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CBSE Class 10 Science past-paper question from the 2025board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.