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Science · 2023 · 5 marks
CBSE 2023 · Region 6 · Set 2 · Q35
(a) (i) What is meant by resistance of a conductor? Define its SI unit. (ii) List two factors on which the resistance of a rectangular conductor…
(i)
What is meant by resistance of a conductor ? Define its SI unit.
(ii)
List two factors on which the resistance of a rectangular conductor depends.
(iii)
How will the resistance of a wire be affected if its
(1)
length is doubled, and
(2)
radius is also doubled ? Give justification for your answer.
In an electric circuit three bulbs of $\displaystyle 100$ W each are connected in series to a source. In another circuit set of three bulbs of the same wattage are connected in parallel to the same source.
(i)
Will the bulb in the two circuits glow with the same brightness ? Justify your answer.
(ii)
Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit ? Give reason for your answer.
Marking-scheme solution
(a)(i)
The property of conductor to resist the flow of charges through it.
If potential difference across the two ends of a conductor is 1V and the current through it is $\displaystyle 1$ A , then resistance ' R ' of the conductor is \(\displaystyle 1 \Omega\).
Alternate answer
\[1 \Omega=\frac{1 \text { volt }}{1 \text { ampere }} \quad / \quad \frac{\mathrm{lV}}{1 \mathrm{~A}}
\]
(ii)
Length of the conductor
Area of cross-section of the conductor
Nature of the material
Temperature
(iii)(1)
The resistance will become one half of its original value.
\[\begin{gathered}
\mathrm{R}=\rho \frac{1}{\mathrm{~A}}=\rho \frac{1}{\pi \mathrm{r}^{2}} \\
R^{\prime}=\frac{\rho \cdot 2 L}{\pi(2 r)^{2}}
\end{gathered}
\]
(2)
\[R^{\prime}=\frac{\rho . l}{\pi(2 r)^{2}} \cdot \frac{2}{4}=\frac{R}{2}
\]
Resistance will reduce to one half.
(b) (i) No
In series combination overall resistance will increase hence decreasing the current . Potential difference also divides. Therefore power consumption is less by each bulb and glows with less brightness.
In parallel combination each bulb will get the required potential difference hence the required current and will glow with its normal brightness.
(ii) None of the bulb glows in series combination as the circuit gets broken and current stops flowing.
In parallel combination the other two bulbs will glow with same brightness as the same voltage is available to them.
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CBSE Class 10 Science past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.