Solenoid - Practice Questions & MCQ

Solenoid -

Solenoid is defined as a cylinderical coil of many tightly wound turns of insulated wire with generally diameter of the coil smaller than its length. 
The solenoid have two ends and one end behaves like the north pole while the opposite end behaves like the south pole. As the length of the solenoid increases, the interior field becomes more uniform and the external field becomes weaker which can be seen from the diagram. 

As the current flows a magnetic field is produced around and within the solenoid. The magnetic field within the solenoid is uniform and parallel to the axis of solenoid. Here we will discuss two cases, one with solenoid having finite length and other when the solenoid is of infinite length. 

(i) Finite length solenoid :

Let n = number of turns per unit length    $\frac{N}{L}$

whrere, N = total number of turns,

              = length of the solenoid

The magnetic field inside the solenoid at point P is given by - 

$
B=\frac{\mu_0}{4 \pi}(2 \pi n i)[\sin \alpha+\sin \beta]
$

(ii) Infinite length solenoid -

If the solenoid is of infinite length and the point is well inside the solenoid. So in this case the angle $\alpha$ and $\beta$ will be $\frac{\pi}{2}$. SO if we put this value in the equation of finite length you will get -

$
B_{\text {in }}=\mu_0 n i
$

Here again, $\mathrm{n}=$ number of turns per unit length.

Note -  Magnetic field outside the solenoid is zero.