At a point in São Paulo (a Brazilian city), the earth's magnetic field vector has magnitude \( B_{\small E}=8 \pi \times 10^{–6} \mathrm T \). At this point, a solenoid is placed so that its axis is parallel to the Earth's magnetic field \( {\vec B}_{\small E} \). The length of the solenoid is 0.25 m, and it has 500 turns. Calculate the magnitude of its current so that the magnetic field inside it is zero. Vacuum Magnetic Permeability   \( \mu_0=4\pi \times 10^{-7}\;\mathrm{\frac{T.m}{A}} \).

Solution