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•    When a current is passed through a conductor, a magnetic field is produced around it. Hans Christian Oersted was the first one to demonstrate this effect practically.
•    Fleming’s right hand thumb rule or Maxwell’s screw rule is used to determine the direction of produced magnetic field around the conductor. Right hand rule states that if a current-carrying conductor is held in the right hand in such a way that the thumb points along the direction of the current, then the curled fingers give the direction of the magnetic field produced by the current.

                                                             

•    Maxwell’s screw rule states that if a screw placed parallel to a conductor carrying current, such that on turning, it advances in the direction of the current, then the direction in which the thumb rotates, gives the direction of the magnetic lines of force.

                                                       

•    The produced magnetic field lines possess some properties. They are in the form of concentric circles and their plane is at right-angles to the straight conductor. Direction of magnetic lines reverses with reversal of direction of current. Increase in the strength of current in the conductor, increases number of magnetic lines around it. Conductor on a whole is surrounded by magnetic lines.
•    When an electric current is passed through a circular coil, the magnetic field lines close to the coil are almost concentric circles, but moving radially towards the centre of the coil, the magnetic lines of force becomes less and less curved i.e. they tend to straighten and at the centre of the coil, the magnetic field lines become straight and perpendicular to the plane of the coil.

                                       
 

•    When the current through the coil flows in the anticlockwise direction, the direction of magnetic field lines, at the centre of the coil, are directed outwards i.e., towards the observer. When the current through the coil flows in the clockwise direction, the direction of magnetic field lines at the centre of the coil, are directed inwards i.e. away from the observer.
•    The strength of the magnetic field produced in the coil by a current passing through it increases on increasing the current flowing through the coil, increasing the number of turns in the coil, decreasing the radius of the coil.

 

       

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