1. WEDNESDAY(04/15): Intro. to Ch.27 - Quantum Theory. Quantization

of Energy. Models of the Atom. HW: Read and Study pages 723-27, then

solve problems 46, 47, 48, 50, and 51 on pages 742-3.

2. THURSDAY(04/16): The Photoelectric Effect. HW: Read and Study pages

728-32, then solve problems 52, 53, 55, 56, and 57 on page 743.

3. FRIDAY(04/17): Lab experiment on Quantum Thinking. HW: Process lab

data, Lab Report due Tuesday.

4. MONDAY(04/20):  Post-Lab Discussion and Applications. HW: Write Lab

Report, due Tuesday.

5. TUESDAY(04/21): The Compton Effect and Matter Waves. HW: Read and

Study pages 733-37, then solve problems 60, 61, 62, 63, 64, 66, and 68 on

page 743.

6. WEDNESDAY(04/22):  REVIEW I Chapter 27. HW: Study page 741 and

complete Review Handout.

7. THURSDAY(04/23): REVIEW II Chapter 27. HW: Complete Review Handout.

8. FRIDAY(04/24): TEST on Ch.27 - Quantum Theory. HW: Visit the

web-site for notes and plans for Ch.28 - The Atom.

1. Early atomic models were single indivisible particle, "plum pudding" model, and

planetary model.

2. The photoelectric effect involves electrons acquiring energy by absorbing particles

of light (photons). These energetic electrons are then termed "photoelectrons".

3. The "200-Year debate" (Light. What is it? Waves or particles?) was revived when

it was observed that a metal plate emitted electrons when struck with light from

a spark discharge.

4. The photoelectric effect contradicts classical physics, but can be explained

assuming that energy is quantized, or occurs in discrete bundles or units.

5. In the visible range, the frequency of light determines its color. Red light is at

the lower end of the frequency scale, and violet is at the upper.

6. Max Planck (1858-1947), determined the value of h, which came to be known

as Planck's Constant, h = 6.6x10^-34 Js. The energy of a photon, or light quantum,

depends on the frequency of the light, E = hf .

7. Heinrich Hertz (1857-1894) experimented with electromagnetic waves and

confirmed the work of the theoretical physicist, James Clerk Maxwell (1831-1879)

who postulated their existence. The unit of frequency is the Hertz (Hz).

8. The minimum energy required for an electron to escape from a metal depends

on the threshold frequency of the metal. This is known as the work function which

is W_o = hf_o , with f_o, this time, being threshold frequency.

9. The maximum kinetic energy of photoelectrons is then found by using the

equation KE_max = E - W_o = hf - hf_o . Another way to determine is by using a

"stopping potential", KE_max = qV_o .

10. Light now has a dual nature, wave and particle, but each particle has no

mass. We call these mass-less particles, photons.

11. The wave equation for light still applies, v = f·λ which is the velocity of a

wave equals the product of its frequency and wavelength. v = c = 3.0x10⁸ m/s ,

the speed of light.

12. Ernest Rutherford (1871-1937) performed the scattering experiment (Gold-Foil)

revealing that all of atom's positive charge and almost all of the mass is at the

center, or nucleus. Most of the atom is empty space.

13. Robert Millikan (1868-1953) determined the charge on the electron with his

famous "Oil-Drop" Experiment. He found that charge, q, is quantized, or only

occurs in multiples of the elementary unit of charge, 1.6x10^-19 C. His equation

was qE = mg.

14. Sir Joseph J. Thomson (1856-1940) found the mass-to-charge ratio for the

electron by experimenting with the CRT. His equations were Bqv = mv²/r and

qE = Bqv , which produced v = E/B and m/q = Br/v .

15. Since each gas has a unique emission and absorption spectrum, the Danish

Physicist, Niels Bohr (1885-1962) proposed a Quantum-Mechanical Atomic Model

instead of Rutherford's Planetary Model.

16. He proposed that electrons can move from one energy level to another by

absorbing or emitting photons. His equations were r_n = 5.2x10^-11 m x n² , and

E_n = -13.6 eV x 1/n² , with n = 1,2,3,... , the energy level. The electron-volt

(eV) is the energy unit for electrons, 1 eV = 1.6x10^-19 J .

17. Count Louis Victor de Broglie (1892-1987) postulated that, "if waves can

have particle properties, why can't particles have wave properties?". His equation

was λ = h/mv for the wavelength of a matter particle.

18. Albert Einstein (1879-1955) explained this, as well as the photoelectric effect,

to get the Nobel Prize in 1921 for his work in 1905. This is why, 100 years later,

2005 was the "World Year of Physics". His famous equation is E = mc² .

19. Werner Heisenberg (1901-1976) determined that it is not possible to know

the exact position and momentum of the electron, the Uncertainty Principle.

20. Arthur Holly Compton (1892-1962) bombarded a graphite block with X-rays

demonstrating the momentum of photons (The Compton Effect ). The equation

is mv = p = h/λ .

21. James Chadwick (1891-1974) an original member of Rutherford's research

team proved the existence of neutrons in 1932.

22. Light Amplification by Stimulated Emission of Radiation (LASER), which

was explained by Einstein in 1917, was invented in 1960. Laser light is very

directional, powerful, monochromatic, and coherent, making it very useful.

23. And to get full credit for your homework make sure you are following

these steps

(i) read the problem and identify the given variables

(ii) determine what you are asked to solve for

(iii) find the correct formula to use

(iv) use algebra to isolate the unknown

(v) substitute-in the given information and simplify.

Answers to Homework: (Scrambled Format.)