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Physics · 2023 · 3 marks
CBSE 2023 · Region 4 · Set 2 · Q29
Two infinitely long parallel conductors A and B, separated by 2 cm, carry 6 A and 2 A currents in opposite directions respectively. Find: (a) the net…
Two infinitely long parallel conductors A and B , separated by $\displaystyle 2$ cm , carry $\displaystyle 6$ A and $\displaystyle 2$ A currents in opposite directions respectively. Find :
(a)
the net magnetic field at a point midway between A and B .
(b)
the force acting per unit length on $\displaystyle \mathrm{B}$.
Marking-scheme solution
(b) Force per unit length
$\displaystyle 1$
\[\text { (a) } \begin{aligned}
\mathrm{B}_{1} & =\frac{\mu_{0} I_{1}}{2 \pi r}=\frac{2 \times 10^{-7} \times 6}{1 \times 10^{-2}} \\
& =1.2 \times 10^{-4} \mathrm{~T} \quad \text { into the page }
\end{aligned}
\]
\[\begin{aligned}
\mathrm{B}_{2} & =\frac{\mu_{0} I_{2}}{2 \pi r}=\frac{2 \times 10^{-7} \times 2}{1 \times 10^{-2}} \\
& =0.4 \times 10^{-4} \mathrm{~T} \quad \text { into the page }
\end{aligned}
\] \(\displaystyle \because \mathrm{B}_{1}\) and \(\displaystyle \mathrm{B}_{2}\) are in same direction.
\[\begin{aligned}
\mathrm{B}_{n e t} & =\mathrm{B}_{1}+\mathrm{B}_{2} \\
& =1.2 \times 10^{-4} \mathrm{~T}+0.4 \times 10^{-4} \mathrm{~T}
\end{aligned}
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