Magnetism: Transformers

Magnetism: Transformers


  • A transformer is a device that changes the voltage of an alternating current (AC).
  • It uses the principle of electromagnetic induction to work.
  • A transformer consists of two coils of wire, called the primary and secondary coils, wrapped around a soft iron core.

Structure of Transformers

  • The primary coil is connected to the input voltage (the mains electricity) and the secondary coil is connected to the output voltage (the appliance).
  • The iron core enhances the magnetic field and provides a path for the magnetism to get from the primary coil to the secondary coil.

Working of Transformers: Inducing Current

  • When an AC passes through the primary coil, it generates a changing magnetic field in the iron core.
  • This changing magnetic field induces a current in the secondary coil.

Transformers and Voltage Changes

  • If the secondary coil has more turns of wire than the primary coil, the transformer is a step-up transformer, and the output voltage is higher than the input voltage.
  • If the secondary coil has fewer turns of wire than the primary coil, the transformer is a step-down transformer, with an output voltage lower than the input voltage.
  • Note: While transformers change voltage, an ideal transformer would conserve power, meaning input power equals output power (neglecting minimal power loss in real-world transformers).

Transformers in Everyday Life

  • Transformers are vital for the national grid. Long-distance power transmission is more efficient at high voltage, so step-up transformers are used at power stations to increase the voltage for transmission.
  • Before electricity enters homes, it must be stepped down to a safer level, which is where step-down transformers come in.

Efficiency of Transformers

  • In reality, transformers are not 100% efficient. Some energy is lost as heat due to the resistance of the coils, and minimal amount is lost due to the magnetising and demagnetising of the iron core.
  • Efficiency can be improved by using low-resistance coils, using a laminated iron core to reduce energy losses due to the magnetising/demagnetising process, and using good quality insulation to minimise energy lost as heat.