Answer: (a) If the right hand is held with the thumb pointing along the current, the curled fingers give the direction of the magnetic field. (b) If the thumb, forefinger and middle finger of the left hand are stretched mutually perpendicular, with the forefinger along the field and the middle finger along the current, the thumb gives the direction of the force.
(a) Right hand thumb rule (Maxwell’s corkscrew rule): hold the current-carrying conductor in the right hand with the thumb pointing in the direction of the current; the direction in which the fingers curl around the wire is the direction of the magnetic field lines.
(b) Fleming’s left hand rule: stretch the thumb, forefinger and middle finger of the left hand at right angles to each other. Point the forefinger along the magnetic field and the middle finger along the current; the thumb then points in the direction of the force (motion) on the conductor.