TRANSFORMER

How does a transformer increase of decrease the voltage?
A transformer is an electrical device that transfer electrical power from one circuit to another. It can raise or lower the voltage in a circuit with a corresponding decrease in the current. It operates on the principle of mutual induction between two coils which are electrical separate but magnetically linked. A simple transformer consist of soft-iron laminated core over which two separate coil are wound called the primary and secondary coils. The coils are insulated from each other and also from the core. The alternating voltage to be transformed is applied toe the primary coil. This causes a varying magnetic flux in the laminated core, most of which is linked with the secondary coil in which mutually induced alternating voltage is produced. If the secondary coil circuit is closed, a current flows in it and thus electric energy is transferred from the primary coil to the secondary coil. The ratio of the secondary voltage(output Voltage) to the primary voltage (input Voltage) can be shown to be equal to the ratio of the number of turns in the secondary to the number of turns in the primary. By selecting this ratio properly, the transformation can be done from any input voltage to any convenient output voltage.
If the secondary has lesser number of turns than the primary, the output voltage is greater than applied voltage and the device is called a step-up transformer. If the secondary has lesser number of turns than the applied voltage and the device is known as a step-down transformer.
For an ideal transformer, power in the primary is equal to that in the secondary. This implies that the current is transformed in the inverse ratio of the voltage. Thus in a step- up transformer, the voltage increases but the current decreases and in a step-down transformer, the voltage decrease but the current increases.

K.Kannan,
Retired professor of physics ,
Erode, Tamil Nadu