The direction of the magnetic field around a current-carrying wire can be found by using:

Correct answer: (d) The right-hand thumb rule

Explanation

By the right-hand thumb rule, hold the wire in the right hand with the thumb pointing along the current: the curled fingers show the direction of the magnetic field lines, which form circles around the wire.

The other rules do other jobs:

• Ohm's law links voltage, current and resistance (V = IR);
• Fleming's left-hand rule gives the direction of the force on a current-carrying conductor in a magnetic field (as in a motor);
• Lenz's law gives the direction of an induced current.