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Science · 2026 · 5 marks
CBSE 2026 · Region 1 · Set 1 · Q39 (b)
(i) How many bulbs of resistance 8 Ω each should be connected in parallel combination to draw a current of 2 A from a battery of 4 V? (ii) Name the…
(i)
How many bulbs of resistance $\displaystyle 8\ \Omega$ each should be connected in parallel combination to draw a current of $\displaystyle 2$ A from a battery of $\displaystyle 4$ V ?
(ii)
Name the device used for measuring electric current. How is it connected in a circuit ?
(iii)
State Joule's law of heating.
Marking-scheme solution
(i)
$\displaystyle \mathrm{V}=4 \mathrm{~V}, \mathrm{I}=2 \mathrm{~A}$
Resistance of circuit $\displaystyle \mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}}$
$\displaystyle \mathrm{R}=\frac{4}{2}$
$\displaystyle \mathrm{R}=2 \Omega$
Let 'n' be the number of bulbs
$\displaystyle \frac{1}{\mathrm{R}}=\frac{1}{8}+\frac{1}{8}+\frac{1}{8}+\frac{1}{8}+\cdots \mathrm{n}$
$\displaystyle \frac{1}{\mathrm{R}}=\frac{\mathrm{n}}{8}$
$\displaystyle \frac{1}{2}=\frac{\mathrm{n}}{8}$
$\displaystyle \mathrm{n}=4$
Therefore, $\displaystyle 4$ bulbs of resistance $\displaystyle 8 \Omega$ should be connected in parallel.
(ii)
Ammeter
In series
(iii)
Heat generated through a current carrying conductor is directly proportional to square of current, resistance of conductor and time for which current flows in conductor. /
$\displaystyle \mathrm{H}=\mathrm{I}^{2} \mathrm{Rt}$
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CBSE Class 10 Science past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.