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Science · 2025 · 2 marks
CBSE 2025 · Region 1 · Set 2 · Q22
(a) Consider the following circuits: (iii) In which circuit will the power dissipated in the circuit be (I) minimum (II) maximum? Justify your answer.
Consider the following circuits :
(i)
(ii)
(iii)
In which circuit will the power dissipated in the circuit be
(I)
minimum (II) maximum ? Justify your answer.
Two lamps, rated $\displaystyle 100$ W; $\displaystyle 220$ V and $\displaystyle 60$ W; $\displaystyle 220$ V are connected in parallel to electric main supply of $\displaystyle 220$ V . Find the current drawn by the two lamps from the supply.
Marking-scheme solution
(a) Power dissipated will be:
(I) minimum in circuit (ii) and
(II) maximum in circuit (iii)
Justification : Power dissipated \(\displaystyle =\frac{V^{2}}{R}\)
Since voltage is same in three cases, the power dissipation
will be inversely proportional to the resistance of the
circuit.
OR
(b) Voltage \(\displaystyle \mathrm{V}=220 \mathrm{~V}\)
\(\displaystyle \mathrm{P}=\mathrm{V} \times \mathrm{I}\)
Power \(\displaystyle \mathrm{P}_{1}=100 \mathrm{~W} \mathrm{P}_{2}=60 \mathrm{~W}\)
\(\displaystyle \therefore \mathrm{I}_{1}=\frac{P_{1}}{V}=\frac{100 \mathrm{~W}}{220 \mathrm{~V}}=0.45 \mathrm{~A}\)
\(\displaystyle \therefore \mathrm{I}_{2}=\frac{P_{2}}{V}=\frac{60 W}{220 V}=0.27 \mathrm{~A}\)
∴ Total current drawn \(\displaystyle \mathrm{I}=\mathrm{I}_{1}+\mathrm{I}_{2}=0 \cdot 45+0 \cdot 27=0 \cdot 72 \mathrm{~A}\)
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