Result
Field inside a solenoid
(E8.4.1) E8.4 · Solenoids and Toroids →Statement
The magnetic field deep inside a long solenoid with n turns per unit length carrying current I.
Symbols and units
| field inside the solenoid | T | |
| turns per unit length | m⁻¹ | |
| current | A | |
| permeability of free space | 4π×10⁻⁷ T·m/A |
When it applies
Deep inside a long, tightly wound solenoid, far from its ends.
Don't use when
Valid deep inside a long, tightly wound solenoid — the field is weaker and non-uniform near the ends, and essentially zero outside.
Derivation
Apply Ampère's law to a rectangular loop straddling the windings, with one side deep inside the solenoid and one side far outside where B ≈ 0:
Watch out for
Valid deep inside a long, tightly wound solenoid — the field is weaker and non-uniform near the ends, and essentially zero outside.
Connects to