Current Induced by Another Current Carrying Conductor

Electricity and Magnetism are actually interrelated

Initially, we had no idea about electricity and magnetism and thought that both are different concepts.

But it’s only in the $19^{th}$ century, physicists could understand that electricity and magnetism are interrelated.

This was discovered when physicists noticed that current flowing through a wire can produce a magnetic field.

In a similar way, a changing magnetic field produces an electric current in a wire

The relation between electricity and magnetism gave rise to Electromagnetism.

To understand more about this, let’s do a small experiment

Let’s take two coils A and B and place them close to each other.

Now let’s connect an energy source like battery and other components like a switch and a variable resistor to coil A in series.

We are not going to connect any energy source or switch to coil B. Only a Galvanometer will be connected to coil B.

Since there is a battery in coil A circuit, let’s call coil A a Primary coil. And coil B will be called Secondary coil.

When we switch on the Primary coil circuit, the current will start to flow in the circuit starting from zero to maximum.

During this time, the galvanometer will show deflections indicating that current is induced in the secondary coil.

when the current in the primary coil reaches its maximum steady value, then the deflection in the galvanometer will become zero.

This indicates that when a steady current is flowing in the primary coil, no current is induced in the secondary coil.

Now, if we switch off the circuit of the primary coil, then the current drops from maximum to zero.

This time, again galvanometer starts to deflect indicating that current is induced in the secondary coil again.

Let’s see why this happens

So, when we switch on the circuit, the current increases from zero to its maximum.

And as we know that magnetic field generates around a current-carrying conductor,

That means here the magnetic field also started to increase with the current.

Thus magnetic flux related to secondary also changes. (Magnetic Flux is nothing but Magnetic field lines)

We have already learned that changing magnetic field induces a current in the wire. (In the image an AC source is used to show the Induction in a better manner)

Here we can observe that the same thing is happening. (In the image an AC source is used to show the Induction in a better manner)

Thus as magnetic flux linked to secondary coil changes, a current is induced in secondary coil and galvanometer deflects.

Now, when current reaches its maximum steady value then the magnetic field also becomes steady. Thus magnetic flux associated with a secondary coil is not changing.

So when magnetic flux does not change, then-current won't be induced in the secondary coil.

Thus galvanometer stops deflecting when the current reaches a steady value.

When we switch off the primary coil, then-current decreases from maximum to zero.

This change in current changes in magnetic flux linked to the secondary coil, which will result in the induction of current in secondary coil and galvanometer deflects.

So, this experiment shows us how electricity and magnetism are interrelated.

Let’s do a small change in the experiment

By know, we understood that when current is steady flowing, there is no induced current in the secondary coil, as magnetic flux remains constant.

Here, we can change the magnetic flux by moving the secondary coil rapidly.

So, although the current is steady the magnetic flux associated with a secondary coil is changing. Thus, current will be induced in the secondary coil.

Recap

Through the experiments we understood that flow of current generates a magnetic field around the wire

And a change in the magnetic field or flux will induce a current in the secondary coil.

If the current is steady, then magnetic flux won’t change and current will not be induced.

In that case, rapidly moving the coil will change the magnetic flux which will induce a current in the secondary coil

The End