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Science · 2026 · 5 marks
CBSE 2026 · Region 1 · Set 1 · Q39
(a) (i) Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why?…
(a)(i)
Due to change in length and area of cross-section of a conductor, resistance of conductor changes while resistivity does not change. Why ?
(ii)
Conductors of electric toasters and electric iron are made of an alloy rather than a pure metal. Why ?
(iii)
Define the S.I. unit of electric current.
OR
(b)(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
(a)(i)
As Resistance, $\displaystyle \mathrm{R}=\rho \frac{l}{\mathrm{~A}}$, it changes with change in length and area of cross section of conductor.
But resistivity of conductor is the characteristic property of material and hence it does not change.
(ii)
The resistivity of an alloy is generally higher than that of its constituent metals. /
Alloys do not oxidise (burn) readily at high temperatures.
(iii)
$\displaystyle 1$ Ampere is constituted by the flow of $\displaystyle 1$ Coulomb of charge per second. /
\[1 \mathrm{~A}=1 \mathrm{C} / 1 \mathrm{~s}
\]
OR
PAG
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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.