The solenoid is a long coil containing a large number of close turns of insulated copper wire. The magnetic field produced by the current carrying solenoid is similar to the magnetic field produced by a bar magnet. A solenoid is used for making electromagnets.

Differences between a bar magnet and solenoid:

Bar magnet

• It is a permanent magnet.
  
• The strength of a bar magnet cannot be changed.
  
• The polarity (North - South) of a bar magnet cannot be changed.
  

Solenoid

• It is a temporary magnet.
• It acts as a magnet only as long as the current passes through it.
  
• The strength of a solenoid can be changed by changing the number of turns in its coil or by changing the current passing through it.
  
• The polarity of a solenoid can be changed by changing the direction of current in its coil.