Answer: Zero.
- A Very strong
- B Equal to inside
- C Radially outward
- D Zero
Correct answer: D. Zero
Explanation: By Ampere's law, no net current is enclosed by a loop outside the windings, so the magnetic field outside an ideal toroid is zero. The field is confined inside.
The magnetic field around a long straight current-carrying wire forms concentric circles, with direction given by the right-hand rule (point thumb along I, fingers curl in the direction of B).
Concept context
Magnetic force on moving charges and currents, the Biot-Savart law, Ampere's law, and the cyclotron - how electric currents create and respond to magnetic fields.