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: Understanding the Question:
The question asks about the nature and distribution of the magnetic field inside a long solenoid carrying a constant electrical current.

Step 2: Key Formula or Approach:
For an ideal, long solenoid, the magnetic field (\(B\)) deep inside the solenoid is given by:
\[ B = \mu_0 n I \]
where:
\(\mu_0\) is the permeability of free space,
\(n\) is the number of turns per unit length,
\(I\) is the current.

Step 3: Detailed Explanation:

• A solenoid is a long coil of wire wrapped closely in a helical shape. When current passes through it, the magnetic field of each turn adds up.

• Inside a long solenoid, the magnetic field lines run parallel to the axis of the solenoid.

• These parallel, straight, and equally spaced field lines indicate that the magnetic field is uniform in both magnitude and direction inside the solenoid.

• Therefore, the magnetic field strength is the same at all points deep inside the solenoid.

• (Note: Near the ends of the solenoid, the field lines start to diverge, and the field strength drops to approximately half of its central value, but the core characteristic is considered uniform/same at all points inside).


Step 4: Final Answer:
The magnetic field inside a current-carrying long solenoid is same at all points.