Great Ideas in Science: Lecture 4 Electricity and Magnetism

1. Great Ideas in Science:Lecture 4Electricity and Magnetism Professor Robert Hazen UNIV 301 Great Idea: Electricity and magnetism are two different aspects of one Force — the electromagnetic force.

2. Electricity and magnetism are two aspects of the same force. All magnets have both north and south poles Static electricity is manifest as a force between charged objects Electricity produces magnetic effects Moving magnets produce electricity

3. Tonight’s Outline • Nature’s Other Forces • Magnetism • Static Electricity • Batteries and Electric Circuits • Magnetic Effects from Electricity • Electrical Effects from Magnetism • Electromagnetic Radiation

4. Magnetism • Magnetic Force • Natural magnetic minerals • Earth is a giant magnet • Used in navigation • William Gilbert • All magnets are dipoles • Like repels, unlike attracts • Earth is a dipole magnet • Magnetic Field

5. Magnetism at Different Scales • Northern Lights • Magnetic Bacteria

6. Static Electricity • Newton’s First Law • Greeks’ Observations • Electrical charge • Electricity • Static electricity • Two kinds of charge • Opposites attract • Like repels

7. Benjamin Franklin, ca.1750 • Benjamin Franklin – single electrical fluid • Transfer of electrons • Positive and negative charges • Atomic structure

8. Lightning Lightning occurs when the negatively-charged clouds interact with the positive charged ground

9. Lightning Lightning occurs when the negatively-charged clouds interact with the positive charged ground

10. The Lightning Rod Electrons are conducted harmlessly from clouds into the ground

11. Coulomb’s Law, ca.1785

12. Coulomb’s Law, ca.1785 • Charles Coulomb • Experiments • Coulomb’s Law: • Force is related to charge and distance • 1 Coulomb = 6.3 x 1018 electrons

13. Force of Electricity vs. Gravity Coulomb’s Law: Fe = ke(q1 X q2)/d2 Gravitational Force: Fg = kg(m1 X m2)/d2

14. The Electrical Field • The force felt by a charge located at a particular point • Differs from the magnetic dipole field

15. Frogs and Animal Electricityca. 1790

16. Frogs and Animal Electricityca. 1790

17. Alessandro Volta’s Response (ca.1800)

18. Alessandro Volta’s Response (ca.1800)

19. The Battery

20. The Battery

21. Three Parts of an Electric Circuits • Source of electrical energy • Closed path • Device to use electrical energy

22. Electric Circuits

23. Electric Circuits

24. Two Kinds of Electric Circuits Series circuit vs. parallel circuit

25. Ohm’s Law • Flow of Electricity • Current (amps) • 1 amp=1 coulomb/sec • Voltage (volts) • Amount of power in circuit • Electrical Resistance (ohms) • Ohm’s Law • Current is directly proportional to voltage and inversely proportional to resistance • Equation: • Load • Equation:

26. Hans Christian Oersted, 1820

27. The Electromagnet

28. Magnetic Effects from Electricity

29. Magnetic Effects from Electricity

30. The Electric Motor North and South poles flip during rotary motion.

31. The Electric Motor North and South poles flip during rotary motion.

32. Michael Faraday, 1831Electrical Effects from Magnetism

33. Michael Faraday, 1831Electrical Effects from Magnetism • Electromagnetic induction • Electrical fields and currents can be produced by changing magnetic fields

34. Electric Generators • Move a coil of wires next to magnets to create electricity • Car alternator • Turbines (power plants) • Wind • Water • Steam - Coal/Nuclear power plants

35. James Clark Maxwell, 1855

36. Maxwell’s Laws, 1855 Four equations describe the behaviors of electricity and magnetism 1. Coulomb’s Law of static electricity 2. All magnets have both north and south poles 3. Electricity produces magnetic effects 4. Moving magnets produce electricity These equations lead to prediction of waves: 1. Waves travel 186,000 miles per second 2. Light is a consequence of electricity and magnetism switching back and forth

37. The Electromagnetic Spectrum • Maxwell’s equations predict more waves • Hertz discovers radio waves