The solenoid and the toroid are two pieces of equipment which generate magnetic fields. The synchrotron uses a combination of both to generate the high magnetic fields required. In both, solenoid and toroid, we come across a situation of high symmetry where Ampere's law can be conveniently applied. By long solenoid we mean that the solenoid's length is large compared to its radius. It consists of a long wire wound in the form of a helix where the neighbouring turns are closely spaced. So each turn can be regarded as a circular loop. The net magnetic field is the vector sum of the fields due to all the turns. Enamelled wires are used for winding so that turns are insulated from each other. As the solenoid is made longer it appears like a long cylindrical metal sheet. The field outside the solenoid approaches zero. We shall assume that the field outside is zero. The field inside becomes everywhere parallel to the axis. Consider a rectangular Amperían loop abcd. Along cd the field is zero as argued above. Along transverse sections bc and ad, the field component is zero. Thus, these two sections make no contribution. The direction of the field is given by the right-hand rule. The solenoid is commonly used to obtain a uniform magnetic field.
The field outside the solenoid approaches the value of:

Options

A. Zero
B. One
C. Two
D. Three

Answer

A

Explanation

The field outside the solenoid ap proaches zero. We shall assume that the field out side is zero. The field inside becomes everywhere parallel to the axis.