Magnetic Effects of Electric Current

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Magnetic Effects of Electric Current

Magnetic Field due to Current Carrying Conductor

In 1819, it was discovered by a Danish Physicist, Hans Christian Oersted that an electric current is always accomplished by certain magnetic effect. He observed a electric current carrying conductor when placed near a magnetic needle; the needle deflects to a certain direction. He also observed that when the direction of electric current in the conductor is reversed, the needle deflects in opposite direction. 

That means there is a magnetic field due to electric current carrying conductor. Further investigation shows that, the magnetic field around the conductor consists of a number of concentric closed lines of force. If we pass an electric current through a conductor through a card board as shown in the figure and try to plot the field with the help of a magnetic needle on that card board, we shall get the magnetic lines as shown in figure. These are all closed circles and concentric with the conductor. Now if we reverse the electric current in the conductor and repeat the same experiment as shown in the figure, we shall get the oppositely directed closed circular magnetic lines, concentric with the conductor as shown. 

From the above experiment it is also found that when electric current flows through the conductor in upward direction, the direction of circular magnetic lines are anti clockwise if we observe from the top. On the other hand; if the electric current flows through the conductor in downward direction, the circular magnetic lines are clockwise if we observe from the top.

Properties of magnetic field due to a electric current carrying conductor can be summarized as below,

1. All lines of magnetic field are circular in shape, symmetrical to each other and concentric with the axis of electric current carrying conductor.

2. The radius of the lines of force increases as we go away from the axis of the conductor.

3. The direction of magnetic circular line depends upon the direction of flow of electric current through the conductor.

4. The magnetic flux density of the induced magnetic field around the conductor increases if the electric current flowing through the conductor is increased and it decreases if the electric current is decreased.

Determination of Direction of magnetic field around a Current Carrying Conductor.

There are mainly two popular rules for determining the direction of magnetic field due to a electric current carrying conductor and these are Cork screw rule and Right hand rule.

If the right handed cork screw is held with its axis parallel to the conductor pointing the direction of flow of electric current and the head of the screw is rotated in such a direction that the screw moves in the direction of flow of electric current , then the direction in which the head of screw is rotated, will be the direction of magnetic lines of force.

Right Hand Rule 

If the electric current carrying conductor is held in right hand by the observer so that it is encircled by fingers stretching the thumb at right to the fingers in the direction of flow of electric current then finger tips will point the direction of magnetic lines of force.