Question

The magnetic induction at a point $P$ which is $4cm$ distant from a long current carrying wire is ${10}^{-3}T$. The field of induction at a distance $12$ cm from the same current would be

• A. $3.33\times {10}^{-4}T$
• B. $1.11\times {10}^{-4}T$
• C. $3\times {10}^{-2}T$
• D. $9\times {10}^{-2}T$

Answer 1

Answer: (A)

$3.33\times {10}^{-4}T$

$\frac{B_1}{B_2}=\frac{r_2}{r_1}$
$B_2=B_1\frac{r_1}{r_2}$
$B_2={10}^{-3}\times \frac{4}{12}$
$B_2=3\cdot 33\times {10}^{-4}T$