A current `I = sqrt2` A flows in a circuit having the shape of isosceles trapezium. The ratio of the bases of the trapezium is 2. Find the magnetic induction B at symmetric point O in the plane of the trapezium. The length of the smaller base of the trapezium is `100 mm` and the distance `r=50mm`.

Answer

A, B

Explanation

Magnetic field at `O` due to currents in wires `ab` and `cd` are Zero.

Magnetic field due to current in wire da(say `B_2)` is inwards due to current in wire bc `(say B_1)` is outwards.
`B_1=mu_0/(4pi)i/r_1(sinalpha+sinbeta)`
`B_2=mu_0/(4pi) i/r_2 (sin alpha +sinbeta)`
`B_1gtB_2` as `r_1ler_2`
`:. B_("net") =B_1-B_2` (outwards)