Moving Charges and Magnetism - Result Question 53
54. The magnetic induction at a point $P$ which is at a distance of $4 cm$ from a long current carrying wire is $10^{-3} T$. The field of induction at a distance $12 cm$ from the current will be
(a) $3.33 \times 10^{-4} T$
(b) $1.11 \times 10^{-4} T$
(c) $3 \times 10^{-3} T$
(d) $9 \times 10^{-3} T$
[1990]
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Answer:
Correct Answer: 54. (a)
Solution:
(a) $B=\frac{\mu_0 I}{2 \pi r} \Rightarrow B \propto \frac{1}{r}$
As the distance is increased to three times, the magnetic induction reduces to one third. Hence,
$B=\frac{1}{3} \times 10^{-3}$ tesla $=3.33 \times 10^{-4}$ tesla
