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Magnetic Field Due to a Current-Carrying Conductor

Hans Christian Oersted, professor of physics at Copenhagen in Sweden was the first to discover the connection between electric current and magnetism. Let us perform the famous experiment he performed in the year 1820. We need only a compass needle, a length of a wire, a battery and a switch (or key). Set us the circuit as shown in Fig. A section AB of the wire is set parallel to the magnetic needle. When the key is not inserted the wire and the needle are both pointing North-South. The moment the key is inserted the magnetic needle swings to a new position as shown in Fig. When the current in the circuit is reversed the needle deflects in the opposite direction.

From the above visual tells us which way the North pole (n) of the compass needle will deflect when the current is passed in the wire lying nearer to the needle.

1. When no current is passed, the needle shows no deflection and points along the NS direction.
2. When the current is reversed, the North pole of the needle is deflected towards East.

3. When a current flows from S to N direction, the North pole n of the needle is deflected towards West.

Magnetic effect of current
Whenever current flows through a conductor, magnetic field is produced around the conductor.

An Important Note
It is important to realize that the deflection of the needle is due to the magnetic field and not due to any electric field. We have learnt that there exists an electric field around a charge. When a current flows, through a wire, there is no net charge on the wire. The electrons move from one end of the wire to the other, and the number of electrons entering at one end is equal to the number of electrons leaving the other end, so that the wire stays electrically neutral as the charges move through it. Hence, there is no net electric field around the wire. The needle is deflected by the magnetic field. Thus, a moving charge, i.e. current, produces a magnetic field. By convention, current in a circuit is shown to flow from the positive terminal of the battery to its negative terminal, although electrons actually move in the opposite direction.



How do you locate a current carrying wire concealed in a wall?


We are able to locate a current carrying wire concealed in a wall by detecting the magnetic field due to wire with the help of a compass. 

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