Question

Magnetic field inside a current-carrying long solenoid

• A. is zero.
• B. decreases towards end.
• C. increases towards end.
• D. is same at all points.

Hint:

Parallel and equidistant magnetic field lines always indicate a uniform magnetic field.
Inside a solenoid, the field lines are straight and parallel, meaning the field is uniform (constant) throughout the interior.

Answer 1

The Correct Option is D

Step 1: Picture the solenoid as many loops stacked together.
A solenoid is just a tightly wound coil of many circular turns, and the field of each turn adds to the fields of its neighbours.
Step 2: See what happens deep inside a long solenoid.
Far from the two open ends, the fields from all the surrounding turns overlap so evenly that the resulting field lines run straight and parallel to the axis, all packed at the same spacing.
Step 3: Translate that geometry into physics.
Field lines that are straight, parallel, and equally spaced everywhere inside mean the field \[ B = \mu_0 n I \] has the same magnitude and direction at every interior point, it does not weaken or strengthen as you move from one interior point to another.
\[ \boxed{\text{Same at all points}} \]