Question

State right hand thumb rule. 

A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?

Answer 1

Right hand thumb rule: 

It states that if thumb of the right-hand points along direction of current, then the remaining curled fingers of same hand gives the direction of the magnetic field due to the current. 

⇒Applying right hand thumb rule, we get that the direction of the magnetic field at a point below the wire is from north to south. The direction of the magnetic field at a point directly above the wire is from south to north.