Electromagnetism

1. Electromagnetism • Syllabus • Lesson 01 – The Motor Effect • Lesson 02 – Induction

2. Syllabus - Single Science IGCSE Magnetism • 6.2 recall that magnets repel and attract other magnets, and attract magnetic substances • 6.3 recall the properties of magnetically hard and soft materials • 6.4 understand the term ‘magnetic field line’ • 6.5 understand that magnetism is induced in some materials when they are placed in a magnetic field • 6.6 sketch and recognise the magnetic field pattern for a permanent bar magnet and that between two bar magnets • 6.7 know how to use two permanent magnets to produce a uniform magnetic field pattern Electromagnetism • 6.8 recall that an electric current in a conductor produces a magnetic field round it • 6.9 describe the construction of electromagnets • 6.10 sketch and recognise magnetic field patterns for a straight wire, a flat circular coil and a solenoid when each is carrying a current • 6.11 appreciate that there is a force on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field • 6.12 recall that a force is exerted on a current-carrying wire in a magnetic field, and, how this effect is applied in simple d.c. electric motors and loudspeakers • 6.13 predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field • 6.14 recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current Electromagnetic induction • 6.15 recall that a voltage is induced in a conductor when it moves through a magnetic field or when a magnetic field changes through a coil; also recall the factors which affect the size of the induced voltage • 6.16 describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also describe the factors which affect the size of the induced voltage • 6.17 recall the structure of a transformer, and understand that a transformer changes the size of an alternating voltage by having different numbers of turns on the input and output sides • 6.18 explain the use of step-up and step-down transformers in the large-scale generation and transmission of electrical energy • 6.19 recall and use the relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer • secondary turns / primary turns = output (secondary) voltage / input (primary) voltage • 6.20 recall and use the relationship • input power = output power VP IP = VS IS for 100% efficiency

3. Syllabus – Double IGCSE Magnetism and electromagnetism understand the term ‘magnetic field line’ (P2.19) recall that an electric current in a conductor produces a magnetic field round it (P2.20) recall that a force is exerted on a current-carrying wire in a magnetic field, and, how this effect is applied in simple d.c. electric motors and loudspeakers (P2.21) predict the direction of the resulting force when a wire carries a current perpendicular to a magnetic field (P2.22) recall that the force on a current-carrying conductor in a magnetic field increases with the strength of the field and with the current (P2.23). Electromagnetic induction recall that a voltage is induced in a conductor when it moves through a magnetic field or when a magnetic field changes through a coil; also recall the factors which affect the size of the induced voltage (P2.24) describe the generation of electricity by the rotation of a magnet within a coil of wire and of a coil of wire within a magnetic field; also describe the factors which affect the size of the induced voltage (P2.25).

4. The Motor Effect06/08/2014 • Aim: • To use Flemming’s Left Hand Rule • To explain how a motor works • To construct a motor

5. Fields Bar Magnets Single Science Only handout

6. Opposite Poles Single Science Only

7. Same Poles Single Science Only

8. Fields due to Current

9. Single Science Only Single Coil of Wire Solenoid

10. Magnetic Field Lines There are magnetic field lines around every Magnet Electrical wire (with current flowing through it) Anything magnetic in the field will experience a force Movie

11. Wire in a magnetic field

12. The Catapult (Motor) Effect

13. Motor Effect If a conductor carrying an electric current moves through magnetic field lines at right angles it will experience a force. A charged particle will experience the same effect

14. Fleming's left hand rule

15. Demo with Motor Effect Apparatus

16. Increasing the Size of the Force

17. The motor effect: true or false?

18. Exam Question Single Science Only

19. Exam Question Single Science Only

20. Coil in a Magnetic Field

21. How does an electric motor work?

22. Demo Motor

23. DC electric motor simulation

24. How do we increase motor strength? Would the same strength motor be used in both of these? How can the strength of an electric motor be increased? • increase the current flowing through the coil • increase the strength of the magnet • increase the number of turns on the coil Worksheet

25. The Motor Effectrecap • Aim: • To use Flemming’s Left Hand Rule • To explain how a motor works • To construct a motor

26. Induction06/08/2014 • Aim: • To observe and define induction • To explain how electricity is generated

27. Exam Question

28. Exam Question

29. Inducing current in a wire

30. What is electromagnetic induction? Current Carrying Wire + Magnetic field = Motion Motion + Magnetic field = Current in Wire Changing Magnetic field = Current in wire If they are at right angles to each other

31. Inducing current in a coil

32. Induction • If a magnet is moved near a coil of wire a current is induced in the wire • Faster motion, bigger current • Stronger magnet, bigger current • More turns, bigger current • Change direction of motion, change direction of current

33. Factors affecting induced current

34. How can motion produce a current?

35. What are Generators? A generator is a device that converts mechanical energy into electrical energy. It is the opposite of an electric motor. Power stations use generators to produce electricity on a large scale. Mechanical energy is provided by rotating turbines that can be powered by: • high-pressure steam – in coal, oil, gas and nuclear power stations • wind – in wind turbines • falling water – in hydroelectric power stations

36. How do AC generators work?

37. AC generator simulation

38. Induction: true or false?

39. What is a transformer? The voltage of an alternating current can be changed using a device called a transformer. iron core A transformer contains two coils that are wound around a soft iron core. The alternating current in the primary (input) coil produces an alternating magnetic field. This alternating magnetic field induces an alternating current in the secondary (output) coil. secondary coil primary coil

40. How does a transformer change voltage? The voltage induced in the secondary (output) coil depends on the number of turns on the primary and secondary coils. A step-up transformer has more turns on the secondary coil and so increases voltage. A step-down transformer has fewer turns on the secondary coil and so decreases voltage.

41. How are transformers used to supply electricity?

42. Transformers • Transformers are used to change the voltage from the Primary (input) to the Secondary (output) • They only work with a.c. (alternating current) • Input (Primary) Voltage = Number of Primary Turns Output (secondary) Voltage Number of Secondary Turns • Example Question: • Input voltage = 230 V • Primary turns = 10000 • Secondary turns = 500 • What is the secondary voltage? Worksheet

43. Exam Question Exam QuestionSeparate Science only

44. Induction06/08/2014 • Aim: • To observe and define induction • To explain how electricity is generated

45. USE ME IN THIS PRESENTATION