Electromagnetism

1. Electromagnetism

2. Imagine a world without • Talking on a telephone • Watching TV • Listening to a radio or CD • Not being able to use anything that plugs into a socket

3. Hans Christian Oersted • In 1820 he was doing a demonstration using electric current. • As he passed current through a wire, a compass needle deflected. • He discovered that magnetism is related to electricity.

4. Electricity and Magnetism • Charge at rest  electric field • Charge in motion  magnetic field

5. Electromagnetism Lab

6. Right hand rule # 1 • If straight wire is grasped with the right hand, with the thumb pointing in the direction of current, fingers will purl in direction of magnetic field.

7. Vertical Conductors Out of the page Into the page X

8. Solenoid • Linear coil of conducting wire

9. Right hand rule #2 • When a solenoid is grasped with the right hand, so that the finger curl in the direction of the current, the outstretched thumb will point toward the north pole of the magnetic field.

10. Electromagnet • Solenoid with a soft iron core

11. Demo • How can you make an electromagnet stronger? • How is an electromagnet different than a permanent magnet?

12. Relationship Between Electricity & Magnetism • Electricity can create magnetism • Moving charges create a magnetic field around the wire carrying that current • Can a magnetic field be used to make charges move?

13. Michael Faraday and Joseph Henry • In 1822,faraday wrote a goal in his notebook: “Convert magnetism into electricity” • 10 years later, he and Joseph Henry, another smart high school teacher, independently made the big discovery that changed the world. • They discovered Electromagnetic Induction

14. Electromagnetic Induction • Process of generating a current in a circuit by changing a magnetic field. • Magnetic field lines must be cut perpendicular by relative motion of magnet and conductor. • Either the magnet can move or the wire can move.

15. Factors affecting magnitude of Induced Current • Amount of conductor or coils of wire • Strength of the magnetic field • Speed of motion

16. Right Hand Rule 3 • When the fingers point in the direction of the magnetic field, (toward the south pole of the magnet) and the thumb points in the direction of the motion of the wire, the palm pushes in the direction of the induced current.

17. Electric generator • Invented by Faraday • Converts mechanical energy to electricity • Wire loop (armature) rotates in a strong magnetic field to induce a current

18. What happens when current flows through a wire? • Demo: Lenz’s Law

19. Lenz’s Law • Induced current opposes the motion that induces it • Work must be done to overcome the magnetic repulsion

20. Electric Motor • Has same parts as generator • Converts electric energy to mechanical energy • Current moves through the armature inside a magnetic field, making armature turn.

21. Demo Simple Motor

22. Generators and Motors • Phone has both generator and motor • Mouthpiece has generator to convert motion of voice into electrical impulse • Earpiece has motor to convert electrical energy into mechanical motion of the speaker. • Both contain magnets and electromagnetic devices.