PHY 102 – Atoms to Galaxies

1. PHY 102 – Atoms to Galaxies PHY 102 – Atoms to Galaxies Our early human ancestors most certainly looked at the night sky, and wondered.

2. Waves Chapter 8: Light & Electromagnetism

6. Wave Not a material object, but a moving pattern: bumps on the surface of water, deformations of music strings, variations in air pressure, oscillations of electromagnetic fields, etc.

7. Two types of waves: 1. Transversal:Waves with propagating direction perpendicularto the oscillation direction. 2. Longitudinal:Waves with propagating direction parallel to the oscillation direction.

10. Two principles: 1.Speed: Waves move at a constant speed that is determined by the medium where they travel, rather than the waves themselves. 2.Superposition: If two or more waves arrive simultaneously at the same place, the resulting effect is simply the sum of the effects of the waves.

11. Speed of soundin various media:

12. wavelength l (m): length of the wave frequency f (/s): number of oscillations over time faudible 20 to 20,000 Hz (humans) faudible < 20 Hz faudible > 20,000 Hz Moving bumps and periodic waves(http://members.aol.com/nicholashl/waves/waves.htm)

13. wavelength l(m) frequency f(1/s) faudible 20 to 20000 Hz wave speed v =l f vsound = 340 m/s vlight = 300 000 000 m/s = 300 000 km/s = 186 450 mi/s If Earth-Sun distance is 92 million miles (150 million km), how long for the light from the Sun to reach the Earth?

16. 17th century physics:planets Many 17th century scientists did not believe in “speed of light.” Galileo … 1670's, the Danish astronomer Ole Roemer discovered that Io didn't always appear where it was supposed to be. c = 300 000 km/s 1888, H. Hertz generated EM waves in his lab.

17. In 1673 reported synchronization between two pendulum clocks hanging on the same wall. Christian Huyghens

18. Superposition: If two or more waves arrive simultaneously at the same place, the resulting effect is simply the sum of the effects of the waves. Interference: Result of different waves traveling through the same medium interacting with one another.

19. When periodic waves arrive at the same place from two synchronized sources, or from the same source but traversing two different paths, they produce aninterference pattern. Interference

20. Interference

23. Process by which waves spread out as a result of passing a narrow aperture, or across an edge, typically accompanied by interference between the wave forms produced beyond the aperture or edge. Difraction:

24. Difraction: Thomas Young, 1803.

25. From the mid-1660s on Newton conducted a series of experiments on the composition of light, and established the modern study of optics. He adopted the corpuscular theory of light according to which light is made of tiny particles emitted in all directions by a source. The theory explained well reflection: a reflecting force would push the light particles away from the surface. Reflection Light: Particle or Wave?

26. Newton discovered that white light is composed of the same system of colors that can be seen in the rainbow. Refraction Light: Particle or Wave?

27. Newton’s corpuscular theory of light had a few difficulties, such as explaining refraction. Light: Particle or Wave?

28. From the diffraction experiment with light there is good evidence that light is a wave. Light: Particle or Wave?

29. Light George McCoy

31. So the concept of light as a wave goes beyond the visible spectrum. Question: If light is a wave, what medium is light traveling through on its way from the Sun to Earth? This and other questions were being asked in the 1800’s. The answer is intrinsically related to electricity and magnetism.

32. Light as a wave: Light is an electromagnetic wave traveling through an electromagnetic field.

33. Electricity Form of energy resulting from the existence of charged particles, such as electrons or proton. (Thesaurus Dictionary) From experiments we know that the charge of the proton (+e) exactly equals the charge of the electron (-e), where e = 1.6 x 10-19 coulomb.

34. Electricity Law of conservation of electric charge: During any process, the net electric charge of an isolated system remains constant (is conserved). Fundamental characteristic of electric charges: Like charges repel and unlike charges attract each other.

35. Electricity Coulomb’s Law: The magnitude of the electrostatic force exerted by one point charge q1 on another point charge q2 is directly proportional to the magnitude of the charges and inversely proportional to the square of the distance r between them: F = k q1q2 / r 2 where k= 9 x 109 N m2/C2.

36. Magnetism Two nearby bar magnets either attract or repel each other. The ends of a bar magnet are called northand southmagnetic poles. Each bar magnet has two poles. “Monopoles” are yet to be found.

37. Magnetism Fundamental characteristic of magnetic poles: Like poles repel and unlike poles attract each other. This attraction (or repelling) force is a new type called magnetic force.

38. Magnetism Experiments show that electrically charged objects that are moving exert and feel an additional force beyond the electric force that exists when they are at rest. This additional force is the magnetic force. All magnetic forces are caused by charges in motion.

39. The Electric Atom The planetary model of the atom depicts the atom as almost entirely empty, divisible and made of many parts. Nucleus (constituted of neutrons and positively charged protons) surrounded by tiny negatively charged electrons.

40. The Electric Atom Order of magnitude: the overall size of an atom is about 10-10 m. The nucleus is about 10,000 times smaller than the atom. A scaled-up model of the atom with a nucleus the size of a soccer ball would have the electrons as dust specks several kilometers away.

41. The Electric Atom Order of magnitude: the overall size of an atom is about 10-10 m. The nucleus is about 10,000 times smaller than the atom. A scaled-up model of the atom with a nucleus the size of a soccer ball would have the electrons as dust specks several kilometers away.

42. Faraday’s Law When a wire loop is placed in the vicinity of a magnet and when the loop or the magnet is moved, an electric current is created within the loop for a long as the motion continues, or, A changing magnetic field creates an electric field.

43. The principle of electric power generation

44. Chapter 9: Electromagnetic Radiation

45. Electromagnetic radiation James C. Maxwell, Scottish, in the 1860s developed a theory that unified electricity and magnetism.

46. Electromagnetic radiation Every vibrating charged object creates a disturbance (wave) in its own electromagnetic field. This disturbance spreads outward through the field at light-speed, 300,000 km/s . Light is just such an electromagnetic wave.

47. Electromagnetic radiation Heinrich Hertz, German, in the 1890s demonstrated experimentally that electromagnetic waves can travel in space and induce oscillations at a distance from where they were generated.

48. Electromagnetic radiation Guglielmo Marconi, Italian, in the late 1890s developed wireless telegraphy which became the basis for the radio and television revolution.

49. The Newtonian clockwork model had no room for new phenomena like light traveling in ‘empty’ space  ether Hypothetical medium for transmitting light and heat (radiation), filling all unoccupied space. all attempts to demonstrate its existence, most notably the Michelson-Morley experiment of 1887, produced negative results Ether

50. The special theory of relativity, proposed by Albert Einstein in 1905 eliminated the need for a light-transmitting medium. Field: a region of space characterized by a physical property, such as gravitational or electromagnetic force or fluid pressure, having a determinable value at every point in the region. Field