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Rural Technology

A static device used for transforming electrical energy form one a.c. circuit to another, without any change in the frequency, is called a transformer. It changes the voltage from high to low or low to high with corresponding increase or decrease in current. If it increases the voltage, then it is termed as step up transformer, & if it decreases the voltage, then it is termed as step down transformer. A transformer does not produce electricity & neither it affects the frequency nor the power.

Working Principle of Transformer -

A current carrying conductor is surrounded by a magnetic field. If a switch is placed in the circuit & it is put to ON & OFF alternately , then the magnetic field around the conductor will start to vary. Now if a second conductor connected with a galvanometer is placed near the first conductor, then it will cut the varying magnetic field of the first conductor. Thus according to Faraday's Law an e. m. f. is induced in the second conductor. Which is verified by the deflection of galvanometer. In other words, the transformer works on the Principle of mutual induction.
A transformer does not work on D.C., Since the magnetic flux must be varied so as to obtain mutually induced e. m. f. It the Coils are used in place of conductors, then the coil connected to the source of supply is called a Primary Coil, while the other coil, from which the output is taken, is called a secondary coil.
If A. C. is supplied to a transformer, then an alternating magnetic field is set up around the primary coil, without making and breaking the circuit by a switch. The Primary and Secondary Coils are wound on laminated cores. The A. C. e. m. f. applied to the Primary Coil produces an alternating magnetic field. The field is cut by the Secondary Coil resulting in an e. m. f. to be induced in it. The secondary voltage depends on the ratio of the secondary turns to the primary turns.

Construction of Transformer -

In this stage we consider about a small transformer which is known as moonlight transformer or bell transformer. It consist of body laminated iron core, bobbin, two windings. Body - It is made up of bakelite. It is used to hold the terminals & protection for windings. The core is made of high grade silicon steel lamination. In this type of transformer E & I types laminations are used. The lamination are used to complete the magnetic path, with minimum losses; A Bobbin is made of presto paper, bakelite or nylon. The winding wire is wound on this bobbin. Bobbin is used to support the windings. In this transformer there are two windings. The windings which is connected to the supply is known as Primary winding & which is connected load is known secondary winding. 6 V, 3 w lamp is connected 230 V, 50 Hz A. C. Supply. Due to mutual induction 6 V a. c. supply is induced in secondary winding.

Transformerphoto.jpg A transformer
The transformer are used to distribute electricity known as distribution transformer which are installed in substation. The power transformers are used in transmission line. The construction of this transformer is basically same as above explained transformer.

In Text Question -

Fill in the blanks-

1. _________ changes the voltage from high to low or low to high with corresponding increase or decrease in current.
2. When Voltage is increased into the transformer is called ________.
3. When voltage is decreased into the transformer is called ________.
4. Transformer works on the _________ principle.
5. A small transformer called ________.

Terminal Questions

1. What do you mean by Transformer?
2. What is Primary Coil?
3. What is Secondary Coil?
4. What is a Construction of Transformer?
5. State the working principle of transformer?

Suggested Activities -

Practical -


Connect a small Transformer & Lamp.


Connector , Electrician Screwdriver. Wire- stripper.

Equipment/ Material-

500 m A, 230 V/ 6 V transformer. Battery holder. 6 V, 5 w, miniature lamp. PVC insulated stranded wires.


1. Remove the insulation of PVC. wire.
2. Connect the wire terminals to battery holder.
3. Put the lamp in battery holder.
4. Connect wires to the primary winding.
5. Connect primary winding to the supply.

What you have learnt -

Transformer used for Transforming electrical energy from one A. C. Circuit another. We also learn the working principle of transformer, its construction.

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Rural Technology