SOUTH Pole

1. NORTH Pole SOUTH Pole N S MAGNET MAGNETIC FIELD

2. N S Needle Paper Thumb Nail Copper Cable

3. MAGNETIC CIRCUIT, ELECTROMAGNETISM AND ELECTROMAGNETIC INDUCTION

4. Understand magnetism • Understand the composite series magnetic circuit • Understand the electrical and magnetic quantities • Understand hysteresis • Understand electromagnetism • Determine the magnetic field direction. • Understand electromagnetic induction The end of lesson, students should be ;

5. MAGNET is the material that have two poles NORTH and SOUTH NORTH Pole SOUTH Pole iNTRoDUctION N S

6. N S MAGNETcan be define as Material that can attract piece of iron or metal Needle iNTRoDUctION Thumb Nail

7. S MATERIAL that ATTRACTED by the MAGNET is known as MAGNETIC SUBSTANCES Needle iNTRoDUctION Thumb Nail

8. S The ABILITY to ATTRACT the MAGNETIC SUBSTANCES is known as MAGNETISM Needle iNTRoDUctION Thumb Nail

9. MAGNETIC FIELD is the force around the MAGNET which can attract any MAGNETIC MATERIAL around it. iNTRoDUctION

10. N S FLUXMAGNET is the line around the MAGNET bar which form MAGNETIC FIELD.

11. There are 2 types of MAGNET • PURE MAGNET • MANUFACTURE MAGNET TYpEs of MAGNET

12. PURE MAGNET Known as MAGNET STONE The stone ORIGINALY have the NATURAL MAGNETIC Basically the stone is found in the form of IRON ORE

13. MANUFACTURE MAGNET There are 2 types of MANUFACTURE MAGNET • PERMANENT MAGNET • TEMPORARY MAGNET

14. PERMANENT MAGNET The ABILITY of the MAGNET to kept its MAGNETISM The basic shape of PERMANENT MAGNET • U shape • horseshoe • ROD • Cylinder • BAR

15. PERMANENT MAGNET Horseshoe Rod U shape Cylinder Bar

16. PERMANENT MAGNET • Permanent magnet can be obtained by: • naturally or magnetic induction ( metal rub against natural magnet) • placing a magnet into the coil and then supplied with a high electrical current.

17. PERMANENT MAGNET Permanent magnet used in small devices such as: compass speakers meter

18. BECOME MAGNET only when there is CURRENT SUPPLY to the metal It has magnetic properties when subjected to magnetic force and it will be lost when power is removed. TEMPORARY MAGNET

19. Example : TEMPORARY MAGNET relay electric bells

20. CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX). • Magnetic flux lines have direction and pole. • The direction of movement outside of the magnetic field lines is from north to south.

21. N S N S S S N N The strongest magnetic field are at the magnetic poles . DIFFERENT POLES ATTRACT each other SAME MAGNETIC POLES will REPEL each other CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).

22. N S • FLUX form a complete loop and never intersect with each other. • FLUX will try to form a loop as small as possible. CHARACTERISTICS OF MAGNETIC FORCE LINES (FLUX).

23. Magnetic Flux • Magnetic flux is the amount of magnetic field produced by a magnetic source. • The symbolfor magnetic flux is . • The unit for magnetic flux is the weber, Wb. MAGNETIC QUANTITY CHARACTERISTICS

24. Magnet Flux density • The symbol for magnetic flux density is B. • The unit is tesla, T • the unit for area A is m2 where 1 T = 1 Wb/m. MAGNETIC QUANTITYCHARACTERISTICS

25. Magnet Flux density • Magnetic flux density is the amount of flux passing through a defined area that is perpendicular to the direction of flux MAGNETIC QUANTITY CHARACTERISTICS

26. Magnetic flux density = Tesla MAGNETIC QUANTITY CHARACTERISTICS

27. MAGNETIC QUANTITY CHARACTERISTICS Example 3 A magnetic pole face has rectangular section having dimensions 200mm by 100mm. If the total flux emerging from the pole is 150Wb, calculate the flux density. Area, A Flux, Φ B?

28. Solution 3 Magnetic flux,  = 150 Wb = 150 x 10-6 Wb Cross sectional area, A = 200mm x 100mm = 20 000 x 10-6 m2 Flux density, = 7.5 mT MAGNETIC QUANTITY CHARACTERISTICS

29. MAGNETOMOTIVE FORCE (MMF) The force which creates the magnetic flux in a magnetic circuit is called magnetomotive force (mmf) - The mmf is produced when a current passes through a coil of wire. The mmf is the product of the number of turns(N) and current (I) through the coil. Unit = Ampere Turns (A.T) Formula , Fm = N x I

30. Defined as magnetomotive force, Fm per metre length of measurement being ampere-turn per metre. number of turns Current magnetomotive force MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE) average length of magnetic circuit

31. MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE) Example 1 A current of 500mA is passed through a 600 turn coil wound of a toroid of mean diameter 10cm. Calculate the magnetic field strength. Current, I Turn, N Diameter, d H?

32. Solution 1 I = 0.5A N = 600 l =  x 10 x 10-2m MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)

33. MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE) Example 2 An iron ring has a cross-sectional area of 400 mm2. The coil resistance is 474 Ω and the supply voltage is 240 V and a mean diameter of 25 cm. it is wound with 500 turns. Calculate the magnetic field strength, H

34. Solution 2 I = V/ R = 240 / 474 = 0.506 A l = π D = π (25 x10-2) = 0.7854 m H= H= H= 322.13 AT/m MAGNETIC FIELD STRENGTH,H (MAGNETISING FORCE)

35. PERMEABILITY • For air, or any other non-magnetic medium, the ratio of magnetic flux density to magnetic field strength is constant , • This constant is called the permeability of free space and is equal to 4 x 10-7 H/m. µ0

36. For any other non-magnetic medium, the ratio • For all media other than free space PERMEABILITY

37. r is the relative permeability and is defined as r varies with the type of magnetic material. PERMEABILITY

38. r for a vacuum is 1 is called the absolute permeability. The approximate range of values of relative permeability r for some common magnetic materials are : • Cast iron r = 100 – 250 • Mild steel r = 200 – 800 • Cast steel r = 300 – 900 PERMEABILITY

39. PERMEABILITY Flux density, B Example 4 A flux density of 1.2 T is produced in a piece of cast steel by a magnetizing force of 1250 A/m. Find the relative permeability of the steel under these conditions. H µr?

40. Solution 4 PERMEABILITY

41. Reluctance,S is the magnetic resistance of a magnetic circuit to presence of magnetic flux. Reluctance, The unit for reluctance is 1/H or H-1 or A-T/Wb RELUCTANCE

42. Example 5 Determine the reluctance of a piece of metal of length 150mm and cross sectional area is 1800mm2when the relative permeability is 4 000. Find also the absolute permeability of the metal. S? Length, l µr µ? RELUCTANCE

43. Solution 5 Reluctance, = = 16 579 H-1 Absolute permeability, = RELUCTANCE = 5.027 x 10-3 H/m

44. Is a magnetic iron core produced when the current flowing through the coil. • Thus, the magnetic field can be produced when there is a current flow through a conductor. ELECTROMAGNET

45. The direction of the magnetic field can be determined using the method: 1. Right Hand Grip Rules 2. Maxwell's screw Law. 3. Compass Three rules may be used to indicate the direction of the current and the flux produced by current carrying conductor.

46. is a physics principle applied to electric current passing through a solenoid, resulting in a magnetic field. Right Hand Grip Rule

47. When you wrap your right hand around the solenoid your thumb points in the direction of the magnetic north pole your fingers in the direction of the conventional current Right Hand Grip Rule

48. It can also be applied to electricity passing through a straight wire the thumb points in the direction of the conventional current (from +ve to -ve) Right Hand Grip Rule the fingers point in the direction of the magnetic lines of flux.

49. MAXWELL’S SCREW LAW • Another way to determine the direction of the flux and current in a conductor is to use Maxwell's screw rule.

50. MAXWELL’S SCREW LAW • a right-handed screw is turned so that it moves forward in the same direction as the current, its direction of rotation will give the direction of the magnetic field.