Question

Two parallel, long wires carry currents i₁ and  i₂ with i₁ > i₂ . When the currents are in the same direction, the magnetic field at a point midway between the wires is 10 μT. If the direction of 2 i is reversed, the field becomes 30 μ T. The ratio  i₁ / i₂ is 

(a) 4 

(b) 3 

(c) 2 

(d) 1

Answer 1

Correct option (c) 2

Explanation

Initially when wires carry currents in the same direction as shown. Magnetic field at mid point O due to wires 1 and 2 are respectively