The magnetic induction at a point $P$ which is distant $4\, cm$ from a long current carrying wire is ${10^{ - 8}}\,Tesla$. The field of induction at a distance $12\, cm $ from the same current would be
AIPMT 1990, Easy
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(a) $B = \frac{{{\mu _0}}}{{4\pi }} \cdot \frac{{2i}}{r}$
$==>$ $\frac{{{B_1}}}{{{B_2}}} = \frac{{{r_2}}}{{{r_1}}}$
$==>$ $\frac{{{{10}^{ - 8}}}}{{{B_2}}} = \frac{{12}}{4}$
$==>$ ${B_2} = 3.33 \times {10^{ - 9}}\,Tesla$
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