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Science · 2025 · 3 marks
CBSE 2025 · Region 1 · Set 2 · Q27
(a) Define one ampere. (b) The resistance of a wire of 0.01 cm radius is 14 Ω. If the resistivity of the material of the wire is 44 × 10^-8 Ω m, find…
(a)
Define one ampere.
(b)
The resistance of a wire of $\displaystyle 0.01$ cm radius is $\displaystyle 14 \Omega$. If the resistivity of the material of the wire is $\displaystyle 44 \times 10^{-8} \Omega \mathrm{~m}$, find the length of the wire. (Given $\displaystyle \pi=\frac{22}{7}$ )
Marking-scheme solution
(a)
When $\displaystyle 1$ coulomb of charge flows through any cross section of a conductor in $\displaystyle 1$ second, then the electric current flowing through it is $\displaystyle 1$ ampere. / \(\displaystyle 1 \mathrm{~A} = \frac{1 C}{1 s}\)
(b)
Radius of wire \(\displaystyle = 0 \cdot 01 \mathrm{~cm} = 0 \cdot 01 \times 10^{-2} \mathrm{~m}\)
\(\displaystyle \rho = 44 \times 10^{-8} \Omega \mathrm{~m}\)
\(\displaystyle R = 14 \Omega\)
\(\displaystyle R = \rho \frac{l}{A}\)
\[l = \frac{R \times A}{\rho} = \frac{14 \times 22 \times \left(0 \cdot 01 \times 10^{-2}\right)^{2}}{7 \times 44 \times 10^{-8}}
\]
\[= \frac{10^{-8}}{10^{-8}} = 1 \cdot 0 \mathrm{~m}
\]
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CBSE Class 10 Science past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.