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Theory:

In the previous sections, we learned magnetic field lines produced by a current-carrying circular loop.
 
In this section, we will observe the pattern of the magnetic field produced by a current-carrying circular coil.
 
Steps:
  • Take rectangular cardboard which has two holes.
  • Insert a circular coil having a large number of turns through the holes (normal to the cardboard plane).
  • Join the ends of the coil in series with a battery, key, and rheostat (variable resistance), as shown in the below figure.
9.png
Magnetic field produced by a current-carrying circular coil
  • Spray iron filings uniformly on the cardboard. (You may use a salt sprinkler to spray.)
  • Plug the key
  • Tap the cardboard mildly a few times.
  • Observe the pattern of the iron filings that emerges on the cardboard.
10.png
Pattern of the magnetic field produced by a current-carrying circular coil
 
Observations:
The magnitude of the magnetic field produced by a current-carrying circular wire at its centre is:
  • Directly proportional to the current passing through the circular wire.
BIWhere,BMagnitude of the magnetic fieldICurrent
  • Inversely proportional to the radius of the circular wire.
B1rWhere,BMagnitudeofthemagneticfieldrRadius of the circular wire
  • The strength of the magnetic field can be increased by taking a circular coil consisting of a number of turns of insulated copper wire closely wound together.
  • If a circular coil has 'n' turns, the magnetic field produced by this current-carrying circular coil will be 'n' times as large as that produced by a circular loop of a single turn of wire.