Question

The magnetic field inside a long, straight current carrying solenoid:

• A. is zero
• B. is same at all points
• C. decreases as we move towards its ends
• D. increases as we move towards its ends

Hint:

A long solenoid produces a uniform magnetic field inside it: \( B = \mu_0 n I \), where \( n \) is the number of turns per unit length.

Answer 1

The Correct Option is B

Inside a long, straight current-carrying solenoid, the magnetic field exhibits several important characteristics that make it unique compared to other magnetic field configurations. \smallskip 1.
Uniform Magnetic Field:

The magnetic field inside the solenoid is nearly
uniform throughout the length of the solenoid, except near the ends where edge effects cause slight variations.
This means the magnetic field lines inside are
equally spaced and parallel to each other, indicating a constant magnitude and direction at every point along the interior.
\smallskip 2.
Direction of the Magnetic Field:

The magnetic field inside the solenoid is directed
parallel to the axis of the solenoid. This direction can be determined using the right-hand rule, where if the fingers curl in the direction of current in the coil, the thumb points along the magnetic field inside.
\smallskip 3.
Cause of Uniformity:

The uniform magnetic field results from the
closely spaced, symmetric windings of the solenoid coil. Each turn of the coil produces a magnetic field, and the superposition of fields from all turns leads to a strong, uniform field inside.
Because the coil is long, the magnetic fields at the ends do not significantly affect the field in the central region, leading to a nearly uniform field in the interior.
\smallskip 4.
Practical Importance:

This property of uniform magnetic field inside a solenoid is utilized in many applications, such as electromagnets, inductors, and devices requiring a controlled magnetic environment.
\smallskip In summary, the magnetic field inside a long, straight current-carrying solenoid is uniform in magnitude and direction, aligned parallel to the solenoid’s axis, due to the symmetric and close winding of the coil turns.