CBSE 2025 · Region 1 · Set 1 · Q25 · 2 marks
A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.Define electric power. When do we say that the power consumed in an electric circuit is $\displaystyle 1$ watt ?
A wire of resistance R is cut into three equal parts. If these three parts are then joined in parallel, calculate the total resistance of the combination so formed.
Define electric power. When do we say that the power consumed in an electric circuit is $\displaystyle 1$ watt ?
Marking-scheme solution
(a) \[\begin{aligned}
& \text { Resistance of each part }=\frac{R}{3} \\
& \qquad \begin{array}{c}
\frac{1}{R_{p}}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}} \\
\frac{1}{R_{p}}=\frac{1}{R / 3}+\frac{1}{R / 3}+\frac{1}{\mathrm{R} / 3} \\
\frac{1}{R_{p}}=\frac{3}{R}+\frac{3}{R}+\frac{3}{R}=\frac{9}{R} \\
\Rightarrow \mathrm{R}_{\mathrm{p}}=\frac{R}{9}
\end{array}
\end{aligned}
\] OR
(b)
Electric power is the rate at which electrical energy is
consumed or dissipated in an electrical circuit. / Electric power is electrical energy consumed per unit time.
When 1A current at 1V potential difference flows in a circuit. / Power consumed is 1W when 1J electrical energy is consumed in $\displaystyle 1$ s.
ElectricityResistors in Series and in ParallelApplyvery_short_answermedium
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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.