THE TOPIC OF TRANSFORMER. PHYSICS SLIDES NOTES FOR FORM 4

The summarised slides notes of the topic of Transformer

1. TRANSFORMER Email; [email protected]

2. Transformer The device that changes voltage from one level to another level. The change can be from higher voltage to lower voltage or lower voltage to higher voltage.

3. How does transformer work

4. How does transformer work If a.c. flows through the primary coil, a.c magnetic field is produced. This alternating current magnetic fields cuts the secondary coil.

5. How does transformer work If a.c. flows through the primary coil, alternating magnetic field is produced. This alternating magnetic fields cuts the secondary coil and induces emf in the secondary.

6. How does transformer work This process of inducing e.m.f in the coil of wire by changing current is called mutual inductance.

7. Types of Transformers There are two main types of transformers and these are; step-up transformer Step-down transformer

8. a. S tep-up transformer This changes low voltage to higher voltage or steps up voltage. The secondary coil has more number of turns than primary coil.

9. a. S tep-up transformer

10. b . Step-down transformer This changes high voltage to lower voltage or steps up voltage. The secondary coil has less number of turns than primary coil.

11. b . Step-down transformer

12. Formula in transformers

13. Formula of Transformer.

14. Formula of Transformer.

15. Example An alternating e.m.f of 240V alternating current power supply. The primary coil has 1000 turns and 4000 turns on its secondary coil . The secondary coil is 0.2A

16. Example Calculate; Secondary e.m.f Primary current Power input

17. Example c. Efficiency d. Comment on the answer to (d)

18. a. Secondary e.m.f

19. b. Primary current

20. c . Power input

21. c . Power input

22. d. Efficiency

23. e. Comment on answer of d This is an ideal transformer

24. Exercise 1. Transformer has 66 turns in primary coil and 660turns in secondary coil. The voltage in the primary circuit is 240V. Calculate secondary coil voltage?

25. Exercise The current in the primary coil of a transformer is 5A and the voltage in primary coil is 220V. The voltage on the secondary coil is 10V.

26. Power Losses In Transformer Resistance of windings Eddy currents Self demagnetised Leakage of field lines

27. a . Resistance of windings As current flows in the coils, wires heat up and energy is lost inform of heat. The heat production in the transformer is due to higher resistance.

28. b. Eddy Currents The magnetic field in the transformer changes inducing eddy currents. This heats up the core and energy is lost inform of heat in a transformer .

29. c. Hysteresis losses The magnetization and demagnetization of the core requires energy. This energy heats up the core and is lost as heat energy.

30. d. Magnetic Leakage/Flux Not all magnetic field lines from the primary coil may reach the secondary coil. The lost magnetic field lines leads to lost of power in a transformer

31. Minimize Power Losses Resistance of windings Eddy currents Hysteresis losses Magnetic Leakage/Flux

32. a. Resistance of windings To minimize this loss of energy thick copper wires of low resistance are used. The thick copper wires have low resistance hence minimizing heat loss .

33. b. Eddy Currents To minimize the heat loss the core is laminated and insulated. This reduces the eddy currents induced between laminations.

34. b . Hysteresis losses To minimize this, the core is made up soft magnetic material(soft iron). This is easy to magnetize and demagnetize, reducing heat losses.

35. d. Magnetic Leakage/Flux To minimize this the core is designed in such way that all the magnetic field lines from the primary coil should reach the secondary coil.

36. Notes To completely reduce heat losses in a transformer is impossible. The large transformer uses oil to absorb heat, heat reducing overheating.