1. An long straight wire lies along the z direction. At time , a constant current is switched on. Calculate the vector potential and the electric and the magnetic fields.

1. An long straight wire lies along the z direction. At time , a constant current is switched on. Calculate the vector potential and the electric and the magnetic fields.

2. A conducting wire is bent into a loop of two semicircles, one of radius and the other connected by straight segments. The loop carries a current , which is directed anticlockwise on the shorter semicircle and clockwise on the other one.. Calculate the vector potential at the centre of the loop. Calculate the electric field at the centre. Can you calculate the magnetic field from the expression of the vector potential?