Question

What is Solenoid?

Answer 1

Solenoid : A solenoid consists of a long insulating wire closely wound in the form of a helix. Its length is very large as compared to its diameter.

The magnetic field at a point $P$ on the axis of the solenoid having $n$ turns per unit length is

$B=\frac{\mu_0 n I}{2}(\cos \alpha-\cos \beta)$

Special cases :

• If the solenoid is of infinite length and point $P$ lies near the middle of a solenoid, then

$\alpha=0^{\circ}, \beta=180^{\circ} \quad \therefore B=\mu_0 n I$

• If the solenoid is of infinite length and point is near one end, then

  $\alpha=0^{\circ}, \beta=\frac{\pi}{2} \quad \therefore B=\frac{\mu_0 n I}{2}$