Question

The earths magnetic induction at a certain point is $7\times {10}^{-5}T$. This field is to be annulled by the magnetic induction at the centre of a circular conducting loop $5.0cm$ in radius. The required current is nearly :

• A. $0.56A$
• B. $5.6A$
• C. $56A$
• D. $2.8A$

Answer 1

The correct option is B $5.6A$

Magnetic field at centre of circular loop is $\frac{{\mu }_{0}I}{2r}=\frac{{\mu }_{0}ni}{2r}=7\times {10}^{-5}$
$⟹\frac{2\pi \times {10}^{-7}\times i}{5\times {10}^{-2}}=7\times {10}^{-5}$
$i=\frac{5\times 7}{2\pi }=5.6A$