solenoid field

Question

Magnetic field inside long solenoid (turns per length n, current I) approximately?

RankGuru · Accepted Answer

1. **Ideal Solenoid**: For a long solenoid with closely wound turns, the field inside is strong and uniform, while the field outside is negligible.
2. **Ampere's Law**: $\oint B \cdot dl = B L = \mu_0 (N I)$.
3. **Simplification**: Since $n = N/L$ (turns per unit length):
   - $B = \mu_0 (N/L) I = \mu_0 n I$.
4. **Result**: The internal field is **$B = \mu_0 n I$**, and it points along the axis of the solenoid.

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solenoid field

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