A current through a horizontal power line flows in east to west direction. What will be the direction of magnetic field at a point directly below it when viewed from east end ?

The direction of the magnetic field around a straight current-carrying conductor is determined by the Right-Hand Thumb Rule. According to this rule, if the thumb of the right hand points in the direction of the current, the curled fingers indicate the direction of the magnetic field lines [1]. In this scenario, the current flows from east to west. When viewed from the east end, the current is moving away from the observer. Applying the rule, the magnetic field lines form concentric circles in a plane perpendicular to the wire [2]. For an observer at the east end looking toward the west (direction of current), the fingers curl in a clockwise direction [1]. Therefore, at any point directly below the wire, the field will be part of this clockwise circular path. Options involving parallel planes are incorrect as magnetic fields around straight wires always exist in perpendicular planes [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > Solution > p. 200
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > Activity 12.5 > p. 199