1. ECA1212 Introduction to Electrical & Electronics Engineering Chapter 10: Magnetism by Muhazam Mustapha, December 2011

2. Learning Outcome Be able to utilize and understand the concepts and formula of magnetism Be able to utilize and understand some of the processes and formula of electromechanics Be able to utilize and understand the concepts and formula for transformer By the end of this chapter students are expected to:

3. Chapter Content Units and Formula of Magnetism Units and Formula of Electromechanical Systems Units and Formula of Transformer

4. Magnetism CO1

5. Magnetism Magnetism is a phenomenon that comes alongside electrodynamic phenomenon Moving electrons are known to have spin that is theoretized to cause magnetism The current (opposite of electron) flow causes magnetic field to form circularly according to right hand grip –Current is in thumb direction –Magnetic field direction is the fingers direction CO1

6. Magnetism Right hand grip rule: CO1

7. Magnetism Right hand grip rule: CO1

8. Magnetic Flux Magnetic flux is the imaginary entity that is considered to form magnetism The direction of magnetic flux is the direction of compass aligned with the flux (from magnetic north pole to south pole) Units and symbols: –Magnetic Flux: Ф, Wb (Weber) –Magnetic Flux Density: B, Wb/m 2 or T (Tesla) –Magnetic Flux Intensity: H, A/m CO1

9. Magnetic Flux CO1

10. Magnetic Flux Relationship: If flux density is constant CO1

11. Ampere’s Law Statement: Integral of vector magnetic field intensity H around a closed path is equal to the total current inside the path If the direction of the closed loop is the same as the field direction CO1

12. Ampere’s Law For a single conductor flowing a current of i, this reduces to: Integration along circular path centered at the conductor; same direction as the flux CO1

13. Flux in a Solenoid CO1 B = flux density µ = medium’s permeability N = No. turns on solenoid i = current l = thickness/length of solenoid µ=medium’s permeability µ r = medium’s relative permeability µ 0 =air or free space’s permeability

14. Basic of Electromechanical Energy Conversion CO1

15. Lorenz’s Force Law For motor action: f = il×B If the vectors l and B are perpendicular, f = Bli Right hand rule: Force Current Flux f = mechanical force i = current l = conductor length B = flux density CO1

16. Lorenz’s Force Law For generator action: e = Blv e = voltage v = conductor speed l = conductor length B = flux density CO1

17. Transformer CO1

18. Transformer Transformer is the electric device that changes (either step-up or step-down) the amplitude of its AC input voltage CO1 Input / Primary Output / Secondary Text book Figure 18.34

19. Principle & Symbol Transformer works due to the fact that the magnetic field around the AC current keeps changing The changes in the magnetic field in the primary (input) coil will induce voltage in secondary (output) coil Symbol: CO1 N1N1 N2N2 V2V2 V1V1

20. Voltage Ratio The ratio of the output to input voltages is proportional to the ratio of the no. turns in the output coils to the no. turns in input coils: CO1

21. Efficiency In an ideal transformer, the input power and the output power will be the same In a practical (non-ideal) transformer, the input and output powers are not the same and the ratio is defined as efficiency: CO1

22. Non-Ideal Output Current In a non-ideal transformer, the output and input voltage ratio follows the ratio of output and input coils’ no. turns The output current however will depend on the efficiency: CO1