A power line carries a current from west to east. What is the direction of the magnetic field due to this current at a point 1 m above the line?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → North to south
The magnetic field lines of a long straight current are circles around the wire. These circles lie in planes at right angles to the wire, and their sense is given by the right-hand rule.
Hold the line with the right thumb pointing east, along the current. Above the line, the curled fingers point towards the south.
Option (1) North to south — Correct. At a point above the line, the field points from north towards south.
Option (2) South to north — Incorrect. This is the direction of the field at a point below the line. There the circle runs the other way.
Option (3) East to west — Incorrect. The field of a straight wire is at right angles to the wire at every point. It has no part along the east-west direction of the line.
Option (4) West to east — Incorrect. This is the direction of the current itself. The field around the wire is perpendicular to it.
NCERT (2026-27):
Ampere’s Circuital Law – “… Grasp the wire in your right hand with your extended thumb pointing in the direction of the current. Your fingers will curl around in the direction of the magnetic field.”