Which right-hand rule helps determine the direction of the force on a current-carrying wire in a magnetic field?

• A. First right hand rule
• B. Third right hand rule
• C. Second right hand rule
• D. Fleming's left-hand rule

Answer: (B)

The force on a current-carrying wire in a magnetic field comes from the cross product of the current direction and the magnetic field. To find its direction with the right-hand rule, point your index finger along the current, point your middle finger along the magnetic field, and your thumb will point in the direction of the force on the wire (for positive charges). Some people describe it as the direction the palm pushes. This is the third right-hand rule used for F = I L × B. For a quick check: if the current is to the right and the field goes into the page, the thumb points upward, giving an upward force. Fleming's left-hand rule is a different rule (for motors) and uses the left hand.