Question

The magnetic field inside a solenoid is:
(A) Infinite
(B) Zero
(C) Uniform
(D) Non-uniform

Answer 1

Hint
Study the formation of magnetic fields due to a current carrying element. Try to understand the concept of ampere’s circuital law as an alternative to Biot-Savart law and try applying the right hand thumb rule to find the magnetic field from the direction of current flow.

Complete step by step solution
Solenoid can be defined as an electromagnet which is formed by tightly packed of a long wire in the form of a helix. Since the coil is tightly packed each turn can be regarded as a circular loop.
If the solenoid is carrying a current there will be a magnetic field. The direction of the magnetic field can be given by the right-hand thumb rule. Right hand thumb rule can be defined as if we curl up our fingers around a circular wire in the direction of the magnetic field. The magnetic field will form a closed loop. Inside a solenoid the magnetic field lines will be straight lines and the field will be strong. Outside the solenoid the magnetic field will be weak and the field lines will curl up to form closed loops.

Hence, the magnetic field inside a solenoid will be uniform.

The correct option is (C).

Additional information
The magnetic field can be given by Ampere’s circuital law. It will be
$B = \mathop \mu \nolimits_ \circ nI$
$B$ is the magnetic field.
$\mathop \mu \nolimits_ \circ $ is the permeability of the free space,
$n$ is the number of turns,
$I$ is the current flowing through the solenoid.

Note
The right-hand thumb rule can be applied directly in different situations. If the current is flowing through a straight wire the magnetic field can be given as when we point our thumb in the direction of the current flow the direction of the magnetic field will be given by direction of the curled fingers.