Electromagnetic induction, fleming's right hand rule

 

                      Electromagnetic induction

 

When a current carrying conductor is placed in a magnetic field in such a manner that the direction of the current is perpendicular to the magnetic field , a force is experienced.

This force causes the conductor to move.

 

 

Now suppose that a conductor is moving inside the magnetic field or magnetic field is changing around a fixed conductor.

This was first studied by English physicist Michael Faraday. And faraday made an important discovery that how a moving magnet can be used to generate electric currents.

 

 

To illustrate , how a moving magnet can be used to generate electric currents.

 

Let us take a coil of wire AB with a large number of turns. And the ends of the coil is connected to the galvanometer

 

  And take a bar magnet. And move its north pole towards the end B of the coil. Then we observed that there is a deflection in the needles of the Galvanometer.

This indicates that there is a presence of the current in the coil AB. The deflection gets zero the moment the motion of the magnet stops.

Now , when the north pole of the magnet is withdrawn and away from the coil. Then we get that the deflection of the galvanometer towards the left , it shows that the direction of the current is set up in the direction of the opposite to the first.

 

Now the magnet is placed stationary at a point near to the coil, and the north pole of the magnet is kept towards the end B of the coil. We see that the needle of the galvanometer gets deflected towards the right , when the coil is moved towards the north pole of the magnet. Similarly, the needle of the Galvanometer moves towards left , when the coil is moved away.

 

But when the  coil is placed stationary with respect with the magnet, the deflection of the needle of the galvanometer becomes to zero.

Thus we concluded that when we move the south pole of the magnet towards the end of the B of the coil, the deflection of the meter of the galvanometer is just opposite to the previous case.

There is no deflection in the meter of the galvanometer , when both the  magnet and the  coil are kept stationary.

 

Thus , it is cleared that , the motion of the magnet with respect to the coil produces an induced potential difference , which setup an induced electric current in the circuit.

 

 

 

 

A moving magnet is replaced by a current carrying coil and the current in the coil can be varied

 

 

 

To illustrate the moving current is replaced by a current carrying coil and the current in the coil can be varied, let us take  two different coils of copper wire with a large number of its turns. Now take a non-conducting cylindrical roll , and the coil is inserted over roll.

Now  the coil-1 with large number of turns  is connected in series combination with a battery and a plug key.

And coil-2 with large number of turns  is connected with galvanometer.

When the circuit is completed, and we observed that there is deflection in the needle of the galvanometer. The needle of the galvanometer instantly jumps to one end and just quickly return back to zero.  And it indicates that a momentary current is in coil-2.

Now coil-1 disconnect from the battery. It observe that needle of the galvanometer moves momentarily, but it is in opposite direction. Itmeans that the current is flowing through the opposite direction in coil-2.

 

With this we observe that as the current in the coil-1 reaches either a steady value or zero , the galvanometer in coil-2 shows no deflection.

 

We concluded that a potential difference is induced in the coil-2 when ever the electric current is passing through the coil-1 changing (starting or stopping).

Coil-1 is called as the primary coil

Coil-2 is called as the secondary coil.

 

When in the first coil, the current changes , magnetic field also changes. Thus in the secondary coil , magnetic filed lines also changes. Hence , the change in magnetic field lines associated with the secondary coil is the cause of the induced electric current in it.

 

The process by which a changing a magnetic field in a conductor induces in another conductor is called  electromagnetic induction.

We can induce a current in a coil either by moving it in a magnetic field or by changing the magnetic field around it.

The induced current is found to be highest when the direction of the motion of the coil is at right angles to the magnetic field. In tis situation , we can use simple rule which is called as fleming’s right hand rule, to know the direction of the induced current.

 

 

Stretch the forefinger , middle finger and thumb of the right hand so that they are perpendicular to each other. If the forefinger indicates the direction the direction of the magnetic and the thumb indicates the direction of the motion of conductor and then the middle finger will show the direction of the induced current. This rule is called as fleming’s right hand rule.