**Bar Magnet as an Equivalent Solenoid:**

Magnetic field lines for a bar magnet and a current carrying solenoid Re resemble very closely. Therefore a bar magnet can be thought as a large number of circulating currents in analogy with a solenoid.

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Let i be the current passing through a solenoid, a be the radius of the solenoid, 2l be the length of the solenoid and n be the number of turns per unit length of the solenoid.

Let P be the point at a distance r from the centre at which magnetic field is to be calculated.

The magnetic field magnitude at point P due to the circular element is given by

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