#### 37.

(a) What is a solenoid?
(b) Draw a rough sketch of the pattern of the lines due to solenoid carrying current.
(c) Compare the magnetic behavior of a straight solenoid with that of a bar magnet.
(d) On what factors does the strength of a magnetic field produced by a current carrying solenoid depends?

Ans:

1. Solenoid: A long cylindrical coil of insulated copper wire of larger number of circular turns is called a solenoid.
2. When a electric current is passed though a solenoid, it produces a magnetic field around it. Its magnetic field pattern is shown in the figure.
3. When a current is passed through the solenoid, the current in each circular loop has the same direction, their magnetic effects get added up producing a strong magnetic field. Inside the solenoid, the magnetic field is almost uniform and parallel to the axis of the solenoid.
4. The magnetic field produced by a solenoid is very much similar to that of a bar magnet. One end of the solenoid has N-polarity while the other end has S-polarity. The polarity of any end (face) of the coil can be determined by using clock rule. For all practical purposes, the magnetic field of a solenoid and that of a bar magnet can be taken identical.

5. Factors on which the strength of a magnetic filed produced by a current carrying solenoid depends:
1. Number of turns in the solenoid : The larger number of turns in the solenoid, stronger is the magnetic field produced.
2. Strength of current : The larger the current passed through the solenoid, stronger is the magnetic field produced.
3. Nature of the core material : By winding the coil over a soft iron cylinder, called core, the magnetic field can be increased several thousands times.