Question

Why is the magnetic field approximately zero outside a long solenoid?

Options

• The fields from adjacent turns are in opposite directions outside and cancel each other

• The current cannot flow outside the solenoid windings

• The permeability of free space is zero outside the solenoid

• The magnetic field lines are absorbed by the enamelled insulation

Answer 1

Outside the solenoid, the magnetic fields produced by adjacent turns are in opposite directions and cancel each other, resulting in a field of approximately zero. In contrast, inside the solenoid, the individual fields of each turn superpose constructively along the axis, giving a strong uniform field.