Do Now (3/4/14) (6 minutes)

Pass in last-week’s Do Now and your HW.

Describe in your own words each of the following concepts.

Photoelectric effect Work Function Ephoton

Threshold frequency

Stopping Potential

The voltage V0 that just stops the emission of electrons.

0qVK

K : Maximum Kinetic Energy of the Electron q : the charge of the electron (include the negative sign)

V0 : stopping potential in V or J/C

Current

If electrons are emitted than a current is produced.

The amount of current produced is directly proportional to the intensity of the incident light.

Photons  Act in strange ways:

Often interact with objects as particles Travel as mass-less waves

Photons have no mass but we can calculate their momentum.

(If you want to know how this is possible talk to me outside of class)

Photoelectric Quiz Review

Mr. Davis Baltimore Poly

Online Multiple Choice Quiz review is extra credit.(I have hard copies, IF you can’t access it at home.)

Due on the day of the quiz.

Write an explanation for why each of your answers is correct.

Tomorrow’s Review

Each table will be assigned problems from the review sheet.

You need to be prepared to teach the class how to solve the problems. You will be given poster paper

tomorrow.

Presentations I will randomly call on two group members

to go to the board and solve one of your problems.

Your grade will depend on how well your entire group presents. Make sure everyone knows both problems.

Everyone in the class will be up at the board at sometime. You don’t have to talk but you have to be involved in someway.

Tomorrow’s Review

You will be graded upon:- Conveying Content   - Enthusiasm - Comprehension - Preparedness -

Time-Limit

A bonus will be given to groups with exceptional presentations. (Engaging and informative)

Review

Spend the rest of class finishing up your solutions to your two problems.

Answer sheet is up front.

Tomorrow you will have ten minutes to prepare your poster. Come to class ready to make your poster.

1. The photoelectric effect involves the emission of electrons from

A. the surface of a metal when the metal is heated.

B. the surface of a metal when it is illuminated with electromagnetic radiation.

C. an atom of a material when the material is negatively charged.

D. an atom of a material when the material is heated.

Answer: B

2. The threshold frequency has a value of X. If the frequency of the incident light decreases from 4x to 2x, then the resulting current of photoelectrons

A. Is doubled.B. Is increased by a factor of 4C. Is reduced by halfD. Remains the same

Answer: C

3. A scientist is trying to eject electrons from a metal by

shining a light on it, but none are coming out. To

eject electrons, she should change the light by:A. decreasing the frequencyB. increasing the frequencyC. increasing the intensityD. increasing the wavelength

Answer: B

4. The photoelectric effect is _____a) A relativistic effect

b) The production of current by silicon solar cells when exposed to sunlight

c) The total reflection of light by metals giving them their typical luster

d) The darkening of photographic film when exposed to an electric field

e) The ejection of electrons by a metal when struck with light of sufficient energy

Answer: E

5. Which of the following graphs best shows how photon energy E varies with the wavelength λ of the light?

Answer: C

E

E

E

E

0

0

0

0

0

0

0

0

A .

C .

B .

D .

6. Which of the following correctly identifies the mass and momentum of a photon?

Answer: B

Mass Momentum

a) zero zero

b) zero non-zero

c) non-zero zero

d) non-zero non-zero

7. Concerning the photoelectric effect, which of the following is not true?

A) For most metals, ultraviolet light is needed for the photoelectric effect to occur.

B) Because a faint light contains very little energy, it take as few minutes before electrons are emitted from the metal it is shining upon.

C) A bright light causes more electrons to be emitted than a faint light.

D) Higher frequency light emits electrons with higher kinetic energies. Answer: B

8. According to the quantum theory of light, the energy of light is carried in discrete units calleda)   alpha particlesb)   photoelectronsc)   protonsd)  photons

Answer: D

9. What will likely to happen if a light whose frequency is below the threshold frequency hits a clean metal surface?a) no electron will be ejected from the metalb) fewer electrons will be ejected from the metalc) more electrons will be ejected from the metald) ejected electrons will have higher kinetic

energy

Answer: A