Question

The earth's magnetic field at a certain point is $0.70$ gauss. This field is to be annulled by the magnetic field at the centre of a circular conducting loop $5.0 \, cm$ in radius. The required current is about

• A. $0.66A$
• B. $5.6A$
• C. $0.28A$
• D. $2.8A$

Answer 1

Answer: (B)

The magnetic field at the centre of closed loop is
$ B = \frac{\mu _{0} I ⁡}{2 r ⁡} = \frac{4 \pi \times 1 0^{- 7} \times I ⁡}{2 \times 5 \times 1 0^{- 2}}$
$\text{or} 0 \text{.} 7 0 \times 1 0^{- 4} = \frac{4 \pi \times 1 0^{- 7} \times I }{1 0 \times 1 0^{- 2}}$
$\therefore I = 5 \text{.} 6 \text{A}$