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# Chapter 3 Electromagnetism

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### Chapter 3 Electromagnetism

1. 1. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES
2. 2. By the end of lesson, you will able to: State what an electromagnet is. Draw the magnetic field pattern due to a current in a: a) straight wire b) coil c) solenoid Factors affecting the strength of magnetic field of an electromagnet. Describe applications of electromagnets.
3. 3.  An electromagnet is a temporary magnet when current is passed through the wire winding a soft iron core.
4. 4.  The pattern of magnetic field depends on shape of the conductor. The direction of magnetic field depends on direction of the current.
5. 5.  A magnetic field pattern can be represented by field lines that show the shape of the field. Current flow
6. 6.  The right-hand grip rule
7. 7.  At the centre of the coil: The magnetic field is the strongest because magnetic field lines are close together The field patterns is straight at right angle
8. 8. The direction of magnetic fieldinside the solenoid The pattern of the is opposite to the magnetic field of a direction outside solenoid is similar solenoid. to that of a bar magnet.
9. 9.  The thumb points towards north pole of the magnetic field.  Other fingers indicate the direction of the Right hand grip current in therule for solenoid solenoid.
10. 10. Draw a magnetic field pattern and direction N S
11. 11. Electric bell Magnetic relay Telephone Circuit earpiece breaker
12. 12. Soft iron armatureCurrent flow attracted towards the through magnetic iron core and Spring return the solenoid 1 disconnects from the iron armature to itswhen switch contact. original positionis pressed. 3 and circuit closed 6 again.Soft iron core in solenoid become 2 Contact 5) Circuit iselectromagnet 5 open and no . current flows and electromagnet lose it magnetism. 4 Hammer hits the gong very quickly to produce sound.
13. 13.  Use as a switch to turn on high voltage appliances such as air conditioner to prevents direct contact with human.
14. 14. Current flow through high The bottom of spring voltage at 2nd circuit. contact is bent upwards 5 4 Spring contact 3The iron armature attracts towards electromagnet . 2The iron core magnetised to become electromagnet. 1 When 1st switch is closed, current flow in solenoid.
15. 15. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES
16. 16. By the end of lesson, you will able to: Describe what happens to a current-carrying conductor in a magnetic field. Draw the pattern of the combined magnetic field due to a current-carrying conductor in a magnetic field. Describe how a current-carrying conductor in a magnetic field experiences a force. Explain the factors affecting magnitude of force. Describe how a current-carrying coil in a magnetic field experiences a turning force. Describe how a direct current motor works. State factors affect the speed of rotation of an electric motor.
17. 17.  A magnetic force is produced when a current- carrying conductor is in a magnetic field.
18. 18.  The direction of magnetic force, F acting on the wire can be determine by using Fleming’s Left-hand Rule.
19. 19. - N + SBy using Fleming’s Left-hand Rule, determine: Flow of current Direction of magnetic field Direction of magnetic force
20. 20. N Direction of currentDirection of Force S
21. 21. N Direction of Force Direction of currentS
22. 22. S Direction of currentDirection of Force N
23. 23. S N The direction of magnetic field is parallel to the direction of current. The short wire stays at rest.
24. 24.  When current-carrying conductor is in a magnetic field of permanent magnet, the interaction between two magnetic field produce a force on the conductor. The direction of magnetic field, the direction of current and direction of force are perpendicular to each other. Direction of force Direction of magnetic field Direction of current
25. 25. 1. Permanent 2. Current-carrying 3. The two field magnet produced conductor interact to a uniform, parallel produced a produced a magnetic field. circular magnetic resultant field. magnetic field. N S N S
26. 26.  The two field interact to produced a resultant magnetic field known as Catapult Field. Region of weaker magnetic field- 2 fields act in oppositedirection Region of strong The interaction between magnetic field two magnetic field - 2 fields act in the produce a force on the same direction. conductor
27. 27. + Magnetic Magnetic field N S of Current- field ofpermanent carrying magnet conductor Region of weaker magnetic field Region of strongmagnetic field
28. 28. Magnetic Magnetic field field of permanent N S + of Current- carrying magnet conductor Region of Region of stronger weaker magnetic N S magnetic field field - 2 fields- 2 fields act in theact in sameopposite direction.direction Direction of force Catapult field
29. 29.  Magnitude of current• Current can be increased by increasing the e.m.f of power supply // using thicker wire of same length// shorter wire.• The larger the current in conductor, the larger the force acting on it. Strength of magnetic field• Stronger magnetic field can be produced by using more powerful magnets or by placing the magnet closer to each other to narrow the gap between the poles of the magnets.• The stronger the strength of magnetic field, the larger the force acting on it.
30. 30.  If a current carrying coil is placed in a magnetic field, a pair of forces will be produced on the coil. This is due to the interaction of the magnetic field of the permanent magnet and the magnetic field of the current carrying coil.
31. 31. carrying coil.
32. 32.  Carbon brush: To contact with the commutator so the current from the battery enters the coil. Spring: Push the brush so it will always contact with the commutator. Split ring commutator: To ensure that the forces on the coil turn the coil in one direction only.
33. 33.  The direct current motor uses the turning effect on a current- carrying coil in a magnetic field. Electric motor converts electrical energy to kinetic energy.
34. 34.  Magnitude of current The higher the magnitude of current, the higher the speed of rotation of electric motor. Number of turns of the coil The higher the number of turns of coil, the higher the speed of rotation of electric motor. Strength of the magnetic field The higher the strength of magnetic field, the higher the speed of rotation of electric motor.
35. 35. SUCCESS IS DIRECTLY PROPORTIONAL TO NOBLE VALUES
36. 36. Electromagnetic induction is the production of an electric current by a changing magnetic field. Induced current only produced when there is relative motion between the conductor and the magnetic field lines.
37. 37. o Moving a straight wire • Moving a permanent quickly across a magnet towards one end magnetic field of a solenoid. between two permanent magnets.
38. 38. a)Direction of induced current in a straight wire can be determine by using Fleming’s right hand rule.
39. 39. Determine the direction of current.
40. 40. a)Direction of induced current in a solenoid can be determine by using Lenz’s law. Lenz’s Law:  States that the direction of the induced current in a solenoid is such that its magnetic effect always oppose the change producing it.
41. 41.  Lenz’s law is an example of the Principle of Conservation of Energy. When the magnet or solenoid is moved against the opposing force, work is done. Therefore mechanical energy is converted to electrical energy.
42. 42. The magnitude of the induced e.m.f is directly proportional to the rate at which the conductor cuts through the magnetic field lines.The size of the induced e.m.f. and thus the inducedcurrent can be increased by:•moving the magnet or the solenoid at a higher speed.• increasing the number of turns on the solenoid.• increasing the strength of the magnetic field throughthe use of a stronger magnet.
43. 43.  A generator is essentially the opposite of a motor which converts mechanical energy to electrical energy.
44. 44.  The two ends of the coil are connected to two slip rings which rotate with the coil.
45. 45.  Coil AB move downwards and coil CD move upwards. Induced current flows from D to C and from B to A. In external circuit, current flows from P to Q. The galvanometer deflected to the right.  Side AB and CD are moving parallel to the magnetic field and thus no induced current is produced.  The galvanometer returns to zero.
46. 46.  Coil CD move downwards and coil AB move upwards. Induced current flows from A to B and from C to D. In external circuit, current flows from Q to P. The galvanometer deflected to the left.  Side AB and CD are moving parallel to the magnetic field and thus no induced current is produced.  The galvanometer returns to zero.
47. 47. Angle of rotation/ 0900 1800 2700 3600
48. 48. Direct current (d.c) Alternate current (a.c)A direct current is a current that flows An alternating current is a currentin one direction only in a circuit. which flows to and fro in two opposite directions in a circuit.The magnitude of a direct current It changes its direction periodically.may be:(a) constant(b) changes with time