Question

What is the direction of the magnetic field?

(a) Inside the plane

(b) Outside the plane

(c) Upwards

(d) Downwards

I have been asked this question during an internship interview.

My enquiry is from Pair Productions in section Quantum Physics of Engineering Physics I

Answer 1

Right choice is (b) Outside the plane

The best I can explain: Form the figure, we realize that the positron rotates anticlockwise while the electron rotates clockwise. Thus, the magnetic field would cause a positive charge to rotate anticlockwise. Using the Right-hand thumb rule, the direction of the magnetic field is outwards the plane.