A transformer works on the principle of Faraday’s Law of Electromagnetic Induction. Let us understand how this phenomenon helps us increase and decrease the voltage in circuits using a transformer. 

This law is at the crux of the link between electricity and magnetism. It defines how current flows through a conductor because of a magnetic field and vice versa.

Faraday’s Laws of Electromagnetic Induction

Faraday’s first Law states that when a conductor is placed in a varying magnetic field, an electromotive force is induced. A closed conductor circuit induces a current. This the induced current. The magnetic field can be variable due to various reasons such as- 

• The conductor moves in and out of the magnetic field
• The magnetic field is not static, it keeps changing in direction and intensity, called magnetic flux. 

Faraday’s first law. Source- the electrical guy

Faraday’s second law states that the induced emf in a coil is equal to the rate of change of flux linkage. Mathematically, it is shown as,

where, 

is the induced electromotive force (EMF).

N is the number of turns in the coil.

is the magnetic flux linked with the coil.

is the rate of change of magnetic flux.

Transformer Works on the Principle of Electromagnetic Induction

A transformer works on the principle of Faraday’s Law of Electromagnetic Induction. When alternating current flows through a conductor or wire, the magnetic field generated constantly changes in intensity and direction. The magnetic field magnifies when the wire forms a coil. A second coil placed near the first coil becomes magnetized by the first coil, generating an EMF (electromotive force) in the second coil. This occurs because the magnetic field interacts with the electrons in the second coil, inducing a current.

Part of the generated magnetic field does not reach the secondary coil, resulting in wasted energy. To address this a ferromagnetic material like steel core is used. The primary coil (on the input side) and the secondary coil (on the output side) wind around this core. The magnetized iron core effectively guides the magnetic field to the secondary coil, reducing waste and increasing efficiency.

Primary and secondary coils. Source- ResearchGate

Basic construction of a transformer. Source- omgfreestudy

Why is AC current used in a Transformer?

The change in the direction of the current allows the magnetic field to continuously change polarity and intensity. If this did not happen, the magnetic field would remain constant. Faraday’s Second Law dictates that a constant magnetic field would result in zero rate of change in magnetic flux. Hence, no EMF would be generated. Therefore, only alternating current (AC) is used in transformers. Direct current (DC) would generate a fixed magnetic field that cannot induce an EMF in the secondary coil.

Eddy currents

Some current swirls within the iron core, creating eddy currents. These currents lead to energy loss. To minimize this wastage, engineers laminate the iron core, which significantly reduces the eddy currents and improves overall efficiency.

Eddy currents in the core. Source- CircuitGlobe

Working principle of types of transformers

Why do we need transformers in the first place?

Imagine this: the supply voltage in our homes is 220V, but we use it to power everything from microwaves to cell phones. The devices would get damaged. They require much lower voltages to function safely. For example, a microwave needs only a few thousand volts. The transformer reduces the supply voltage to a lower level. This ensures these devices operate safely.

In other cases, such as in power plants where supply lines begin, the voltage required is much higher to minimize energy loss during transmission. Here, generator transformers increase the output voltage for efficient power transmission over long distances.

Principle used by transformers to increase and decrease the supply voltage

Transformer works on the principle of electromagnetic induction. By changing the number of turns in the primary and secondary coils, we can change the final output voltage. The relationship is governed by the formula given below:

where;

is the voltage across the primary coil

is the voltage across the secondary coil

are the number of turns in the primary coil

are the number of turns in the secondary coil

When the number of turns in the secondary coil is greater than in the primary coil the voltage is increased, creating a step-up transformer. 

The reverse occurs when the secondary coil has fewer turns than the primary coil or then, the output voltage is lower than the input voltage, resulting in a step-down transformer.

Transformer Demonstration Model

This model helps you visualize the working principle of a transformer.

Step-down transformer model by Labkafe

This is a step-down transformer which changes the voltage from the mains supply of 220V to around 12V, which you can measure using a multimeter. The model is demountable, therefore easy to store, transport and demonstrate almost anywhere in a school. 

While planning a visit to a power plant or dismantling a device to demonstrate the function of the transformer might not be easy, this model will do the same for you, if not more. 

Contact our lab experts to book the model for your school today!