CBSE 2025 · Region 3 · Set 1 · Q39 · 4 marks

As shown in the diagram, an electric circuit consisting of an ammeter, a voltmeter, $\displaystyle 4$ cells of $\displaystyle 1 \cdot 5 \mathrm{~V}$ each, a plug key with a gap XY was set up. Voltmeter and ammeter readings were recorded in the observation table for four arrangements as given below : Arrangement No. $\displaystyle 1$ - only resistor $\displaystyle \mathrm{R}_{1}$ in gap XY Arrangement No. $\displaystyle 2$ - only resistor $\displaystyle \mathrm{R}_{2}$ in gap XY Arrangement No. $\displaystyle 3$ - Resistors $\displaystyle \mathrm{R}_{1}$ and $\displaystyle \mathrm{R}_{2}$ in series in gap XY Arrangement No. $\displaystyle 4$ - Resistors $\displaystyle \mathrm{R}_{1}$ and $\displaystyle \mathrm{R}_{2}$ in parallel in gap XY

Based on the observations, four V - I graphs A, B, C and D as shown in figure were drawn. Study these graphs.

(a)

Which one of the graphs represents the series combination of $\displaystyle \mathrm{R}_{1}$ and $\displaystyle \mathrm{R}_{2}$ ?

(b)

Which one of these graphs represents the parallel combination of $\displaystyle \mathrm{R}_{1}$ and $\displaystyle \mathrm{R}_{2}$ ?

(c)

(i)OR(c)

Show an arrangement of three resistors, each of resistance $\displaystyle 10 \Omega$, so that the combination has a resistance of $\displaystyle 15 \Omega$. Give justification for your answer.

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.