Question

Can a transformer work when it is connected to dc source ?

Answer 1

Hint:To obtain the solution of this question, we need to understand the working principle, and construction of a transformer. Basically, in a transformer, an AC current produces a magnetic field in one coil which affects the other coil. By principle of electromagnetic induction, the magnetic field will generate current in the other coil. Hence, here we need to find out if all the above conditions can be satisfied by a DC current or not.

Complete answer:
Let us start by understanding the working principle and necessity of a transformer.A transformer is mainly used to either increase the output voltage or decrease the output voltage without loss of power. The transformer used to increase the output voltage is known as step-up transformer and the transformer used to decrease the output voltage is known as step-down transformer.

In a transformer, two coils of conducting wire are closely wound on an iron core having high permeability such that they are all isolated from each other. Out of the coils, one of them is called the primary coil and the other is known as the secondary coil. The primary coil will be connected to an input source and the secondary coil is connected to the output.

Now, let us understand the working of the transformer with an AC source. The primary coil will be connected to the AC source, and an AC current will flow in the primary coil which will periodically change with time. Hence, due to the current a magnetic field and magnetic flux is generated around the primary coil.

As the secondary coil is close to the primary coil, the induced magnetic flux will be linked to the secondary coil. As the magnetic flux is from an AC source, it will be changing periodically with time. From Faraday’s Law, we can say the negative of the time rate of change of magnitude of flux is equal to the induced emf. Hence, an emf will be generated in the secondary coil as per the number of turns in the coil.

Now, if the AC source is replaced by a DC source, the current in the primary coil will be constant. Hence, the induced magnetic field and magnetic flux around it will also be constant. Now, when this constant magnetic flux is linked with the secondary coil, we can understand from Faraday’ Law, which requires a varying magnetic flux to induce emf, for a constant magnetic flux from a DC source, no emf will be induced in the secondary coil.

Hence, a transformer cannot work with a DC source.

Note:We can understand that there is no induced emf in the secondary coil when a transformer is connected to a DC source. As a result of this phenomenon, the net voltage in the primary voltage will increase, due to which more current will be drawn in the primary coil, and there might be chances of burning of the primary coil.