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Theory:

In the previous section, we learned about the pattern of the magnetic field produced by a current-carrying circular coil.
 
In this section, we shall discuss the magnetic field produced by a solenoid.
 
What is a Solenoid?
A coil with number of circular turns of insulated copper wire covered closely in the shape of a cylinder is called a Solenoid.
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Field lines of the magnetic field through and around a current-carrying solenoid
 
The below figure shows the pattern of the magnetic field lines around a current-carrying solenoid.
 
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Pattern of the magnetic field produced by (a) Solenoid (b) Bar magnet
 
Analyse the pattern of the field with the magnetic field around a bar magnet with a solenoid (see the below figure).
 
Do they look similar?

Yes, they are similar.
 
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Magnetic field produced by (a) Solenoid (b) Bar magnet
 
One end of the solenoid functions as a north pole of the magnet, while the other is the south pole.
 
The magnetic field lines inside the solenoid are in the form of parallel straight lines. This shows that the magnetic field is identical at all points inside the solenoid i.e., the magnetic field is uniform inside the solenoid.
 
A strong magnetic field created inside a solenoid can be used to magnetise a piece of magnetic material, like soft iron, when placed inside the coil (see the below figure). The magnet so formed is called an Electromagnet.
 
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Current-carrying solenoid coil is used to magnetise the steel rod inside the coil
  
Increase magnetic field strength in a solenoid by,
  • Increasing the current flowing through it,
  • Increasing the number of turns on the coil per unit length,
  • Inserting a soft iron core into the solenoid.