- two coaxial circular loops L1 and L2 OF radii 3cm and 4cm are placed .what should be the magnitude and direction of the current in loop L2 so that the net magnetic field at O be zero?
Magnetic field at a point on the axis of dipole is given by
B = uo I a2 / 2 (a2 + x3 )3/2
here a is the radius of coil, x is the distance of point from the centre of coil
In order that the magnetic field at O to be zero
B(L1) = B(L2)
uo x I1 x (3) 2 / 2 (32 + 42 )3/2 = uo x I2 x (4) 2 / 2 (42 + 32)3/2
I2 / I1 = (3)2 / (4)2 = 9/16
I2 = I1 x 9/16 = 1 x 9/16 = 0.5625 A
The direction of I2 must be opposite to that of I1