Question

The magnetic field due to current carrying circular loop of the radius $12 \, cm$ at its centre is $0.50\times 10^{- 4} \, T$ . The magnetic field due to this loop at a point on the axis at a distance of $5 \, cm$ from the centre is

• A. $3.5\times 10^{- 9 \, }T$
• B. $5.3\times 10^{- 9 \, }T$
• C. $9.3\times 10^{5 \, }T$
• D. $3.9\times 10^{- 5 \, }T$

Answer 1

Answer: (D)

Use $\frac{B_{a x i s}}{B_{c e n t r e}}=\left(\frac{R^{2}}{R^{2} + x^{2}}\right)^{3 / 2}$
$\frac{B_{\mathrm{axis}}}{0.5 \times 10^{-4}}=\left(\frac{12^2}{12^2+5^2}\right)^{3 / 2}$
$B_{\text {axis }}=\left(0.5 \times 10^{-4}\right)\left(\frac{12}{13}\right)^3$
$B_{a x i s}=3.5\times 10^{- 5}T$