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.
K  qV0
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.
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(If you want to know how this is possible talk to me outside of class)
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.
Photoelectric Quiz Review
Mr. Davis Baltimore Poly
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.
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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 4
C. Is reduced by half
D. 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 frequency
B. increasing the frequency
C. increasing the intensity
D. 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?
A.
0
C.
B.
E
0
0
0
D.
E
0
E
0
E
0
0
Answer: C
6. Which of the following correctly identifies the mass and
momentum of a photon?
Mass
Momentum
a)
zero
zero
b)
zero
non-zero
c)
non-zero
zero
d)
non-zero
non-zero
Answer: B
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 called
a)
b)
c)
d)
alpha particles
photoelectrons
protons
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 metal
b) fewer electrons will be ejected from the metal
c) more electrons will be ejected from the metal
d) ejected electrons will have higher kinetic energy
Answer: A