MAGNETIC FIELDS

1. MAGNETIC FIELDS Pre-Class for Wednesday 5-2-12 True or False: Electricity and Magnetism are related. • Begin next chapter: Ch24: Magnetic Fields • Brief history of magnets

2. Some Definitions • Magnetic Force • The interaction when two magnets are brought close together • Can be attraction or repulsion • Magnetic Field • Represents the effect of a magnet on the area around it • Magnetic Poles • Two for every magnet • Strongest field found here • North (out) and South (in)

6. Observing Magnetic Interference Procedures • Clamp a bar magnet vertically to the ring stand. • Tie string around a paper clip. • Anchor the end of the string under a book. Slowly pull the string until the paper clip floats in the air. • Without touching the paper clip, slide various objects between the magnet and paper clip. • Record observations Equipment needed: paper clip, ring stand, clamp, bar magnet, string

7. Pre-class for Thursday 5-3-12 The location of the strongest magnetic field on a magnet is at the _____. • Magnetic force • Magnetic poles • Magnetic domains • Electromagnets

10. Why a magnetic field? • The mantle is on a tectonic plate, which floats on a river of liquid rock/metal • The magma is flowing, just like a river • Friction between the plates and magma cause charges to move, creating a magnetic field

11. F = B I L F force of magnetic field (N) B magnetic field strength (T or gauss) I current in wire (Amp) L length of wire (m) MAGNETIC FORCE DUE TO A CURRENT-CARRYING WIRE

12. B field I #1 Right Hand Rule • Fingers point direction of magnetic field (curved around the wire) • Thumb point direction of current

13. F = q v B F magnetic force (N) q charge (C) v velocity (m/s) B magnetic field (T or gauss) MAGNETIC FORCE DUE TO A CHARGED PARTICLE IN A MAGNETIC FIELD

14. #2 Right Hand Rule • Fingers point direction of magnetic field • Thumb point direction of motion for the particle • Force on charge due to magnetic field comes out of the palm Works for positive charges only!!!(use left hand for negative)

15. P+ F X e- F B field What direction will the force be?

16. P+ X X X X X X X X X X X X X X X X X X X X F e- F B field What direction will the force be?

17. Pre-class for Monday 5+7=12 Objects that keep their magnetic properties for a long time are called _____. • Permanent magnets • Electromagnets • Magnetic domains • Temporary magnets

18. 59. move left or spin 63. 0.04 T 65. ccw 66. into page; out of page 74. 2.4 N 78. 3000 Amps 84. .742 T; 2.66x1016 m/s2 92. 2.1x10-12 N, upward 60. 0.5 T 61. 0.89 Volts 73. 0.13 Volts; 0.13 Amps; cw; opposite 75. 1,800 Volts; 30 Amps; 3,600 Watts 76. 36 turns; 9.4 mAmps 77. 2:1; 5 Amps 80. 3600 Volts, 90 Amps; 1.1x104 Watts CH 24 HW CH 25 HW

19. Electromagnetic Induction Chapter 25 The process of producing a current in a wire using magnetism

20. Electromagnet • A magnet produced by current electricity • No current, no magnet • Wire must be wrapped to combine the magnetic field produced • A metal (Iron, etc.) core can help, but is not necessary • How magnets are made

21. Materials Wire Battery 10 paper clips Nail or bolt Christmas light Procedures Make an electromagnet Do not complete the circuit until you are ready! Battery will get hot! Fill out the chart with the proper number of turns and paper clips. Objective Construct an electromagnet and pick-up paper clips. Making Your Own Electromagnet

22. Electromotive Force • The voltage produced by a battery to move energy around a wire • It is not a force—it was named this because it was originally thought charges were being “forced” to move around a wire • Units: Volts EMF = B l v sinq

23. Pre-class for Tuesday 5-8-12 Find the direction of the magnetic field on the inside and outside of the solenoid shown.

24. 2 TYPES OF CURRENT • Alternating (AC) Current • Current changes direction • Current flows both ways • Direct (DC) Current • Current flows one direction only • Defined by Ohm’s Law

27. But, not these Transformers!!!

28. TRANSFORMERS • A device used to increase or decrease the voltage in an AC circuit • 2 basic types • Step-up: increase voltage • Step-down: decrease voltage • Used to change the voltage sent from the power company to your house

30. 59. move left or spin 63. 0.04 T 65. ccw 66. into page; out of page 74. 2.4 N 78. 3000 Amps 84. .742 T; 2.66x1016 m/s2 92. 2.1x10-12 N, upward 60. 0.5 T 61. 0.89 Volts 73. 0.13 Volts; 0.13 Amps; ccw; opposite 75. 1,800 Volts; 30 Amps; 3,600 Watts 76. 36 turns; 9.4 mAmps 77. 2:1; 5 Amps 80. 3600 Volts, 90 Amps; 10800 Watts for both CH 24 HW CH 25 HW

31. Pre-class for Wednesday 5-9-12 The function of an electric motor is to _____. • Change electrical energy to chemical energy • Change chemical energy to electrical energy • Change mechanical energy to electrical energy • Change electrical energy to mechanical energy

32. Materials Battery Hand crank generator Light bulbs Switch Objective To make an electric motor and generator Questions Which part models an electric motor? Explain. Which part models an electric generator? Explain. What would happen if a battery with a larger voltage was used? Where is the magnetic field the strongest? Explain. Procedures Connect the hand generator, light bulb, and switch in series. Turn the hand crank and record the light bulb brightness. Remove hand generator and connect battery instead. Record light bulb brightness. Connect battery to hand generator and switch. Close switch. Record observations. Electric Motor or Generator