A current-carrying wire is known to produce magnetic lines of force around the conducting straight wire. The direction of the lines of force may be described by

1. left-hand thumb rule for up-current and right-hand thumb rule for down current
2. right-hand thumb rule for both up and down currents
3. right-hand thumb rule for up-current and left-hand thumb rule for down current
4. left-hand thumb rule for both up and down currents

Answer

Using your right-hand, point your index finger in the direction of the charge's velocity, v. Point your middle finger in the direction of the magnetic field, B. Your thumb now points in the direction of the magnetic force.

The correct option is B.