Author
Bruce Dalzell
Title
Photoelectric Effect
Grade Level
12
Subject Area
Physics
Overview of
unit/lessons/activities
(assumptions of prior
knowledge/learning)
Unit 7: Waves and Modern Physics
Chapter 18: Early Quantum Theory
Topic: 18.1 The Particle Nature of Light: The Photoelectric Effect
Overview
Students begin to examine the differences, similarities, and interactions between particles
and waves.
The photoelectric effect was a significant early demonstration of the quantum nature of
light. The concept of threshold frequency and work function for metals will be examined as
well as the effects of changing the battery voltage difference and the frequency and
intensity of light on the electron velocity and resulting current.
Activities
1. A set of five mini labs using the Photoelectric Effect Simulation - PhET

Large / Small Group Practice / Discovery Learning (using Photoelectric Effect
Simulation - PhET) -

Individual Data Collection and Mathematical / Graphical Analysis of Results (PhET /
DataStudio – work function, threshold frequency)

Reinforcement Activity (PhET – work function)

Individual Concluding Activity (PhET – unknown metal)
2. Teacher-centered instruction and large group discussion of results
Assumptions / Prior Learning

In Physics 11, students have studied particle and wave behaviour having completed
Unit 4: Waves.

The Waves unit included the Universal Wave Equation (c = f λ) and Planck’s
equation (E = hf ) and kinetic energy (EK= ½mv2)

Most Physics 12 students have successfully completed Chemistry 11 and
understand the atomic theory and ionization energy.
Correlations to ICT and
curriculum outcomes
ICT OUTCOMES TEN TO TWELVE
BOC 12.1
use a wide variety of technology, demonstrate a clear understanding of
technological applications, and consistently apply appropriate technology to solve
curriculum problems
BOC 12.2
demonstrate an ability to assess the application of technology to solve
problems, particularly to evaluate significant effects which estimations, program
flaws and human error have on a given solution
PTS 12.5
create electronic charts, tables and graphs; and design, create and
manipulate spreadsheets and databases, as part of the process of collecting,
analyzing, and displaying data independently
CT 12.3 design and create electronic documents to accomplish curricular tasks
RPSD 12.1
select appropriate devices and software to collect data, solve problems and
note patterns; to make logical decisions and draw conclusions; and to present
results, with general supervision
PHYSICS 12 OUTCOMES
115-7
explain how scientific knowledge evolves as new evidence comes to light and as
laws and theories are tested and subsequently
restricted, revised, or replaced
115-3
explain how a photon momentum revolutionized thinking in the scientific
community
213-6
use library and electronic research tools to collect information on a given topic
327-9
describe how the quantum energy concept explains blackbody radiation and the
photoelectric effect
327-10 explain qualitatively and apply the formula for the photoelectric effect
Projected timeline for
preparation and for
carrying out activities
1. Teacher-centered instruction (TCI): Background Concepts and Introduction of the
Photoelectric Effect
Large Group Practice / Discovery Learning: Relating Frequency and Intensity to Current
(Photoelectric Effect Simulation - PhET)
2. TCI: The Effects of Light Intensity and Frequency and The Experimental Work of Lenard
and the Concept of Stopping Potential
3. Small Group Practice / Discovery Learning: Determining Stopping Potential (using
Photoelectric Effect Simulation - PhET)
4. TCI: Einstein, Millikan, Work Function and Threshold Frequency
5. Individual Data Collection and Mathematical and Graphical Analysis of Results:
Determination of Work Function and Threshold
Frequency for a Specific Metal (using Photoelectric Effect Simulation - PhET)
6. Reinforcement Activity : Verification of the Work Function of a Metal from Simulation
Data
7. Individual Concluding Activity: Identification of an Unknown Metal by from its Work
Function and Threshold Frequency (using Photoelectric Effect Simulation - PhET)
Equipment
Requirements:
Data projector and screen – for teacher demonstration of how to use simulation software
(computers, software,
etc)
Computer Lab / COW (internet access) – for pairs of students to play/experiment, collect,
store, and email data between home and school
Web Site: http://phet.colorado.edu/new/simulations/sims.php?sim=Photoelectric_Effect
Software: Data Studio (for graphical analysis)
Teaching materials
provided (Blacklines,
worksheets, templates,
teacher materials)
Text:
Physics (2003). Chapter 18 Early Quantum Theory: The photoelectric effect. McGraw-Hill
Ryerson: Toronto. pp. 843-853.
Files:
SIMULATION EXPERIMENTS
MiniLab 1: Relating Frequency and Intensity to Current
MiniLab 2: Determining Stopping Potential
Figure 1: Graph of Stopping Potential versus Frequency for Sodium Metal
MiniLab 3: Determination of Work Function and Threshold Frequency for a Specific Metal
Lab 4: Verification of the Work Function of a Metal from Simulation Data
Lab 5: Identification of an Unknown Metal by from its Work Function and Threshold
Frequency
NOTES
Introduction of the Photoelectric Effect
The Effects of Light Intensity and Frequency
The Experimental Work of Lenard and the Concept of Stopping Potential
Einstein, Millikan, Work Function and Threshold Frequency
Resources available
for teacher/student use
(websites, references,
etc)
SIMULATION SITE
Photoelectric Effect Simulation - PhET
http://phet.colorado.edu/new/simulations/sims.php?sim=Photoelectric_Effect
ADDITIONAL LESSON PLANS FROM PHET
Intro to Photoelectric Effect Interactive Lecture
S. McKagan Demo
Photoelectric effect
J. Bourne Lab
Photoelectric Effect
C. Miller
Lab
Photoelectric Effect Activity
D. Collins Lab
The Photoelectric Effect
A. Sokolowski
Lab
Understanding the Photoelectric Effect
S. McKagan HW
RELATED WEB SITES
Physics 24/7: Physics Tutorial: Photoelectric Effect and Garage Door Sensors
http://www.physics247.com/physics-tutorial/photoelectric-effect.shtml
Robert B. Friedman & Rick Kessler - The Photoelectric Effect & Its Applications
http://cfcpwork.uchicago.edu/kicp-projects/nsta/2007/pdf/nsta_2007-photoeleclab.pdf
STEAMING VIDEO
A Photoelectric Effect Experiment (Windows Media Audio/Video file)
Detailed instructions
for each activity or
lesson (teacher
notes, activity
information, learning
strategies, teacher
role, student roles)
Unit 7 – Waves and Modern Physics
Chapter 18
Early Quantum Theory
Photoelectric Effect
1. CLASS ONE
A. TEACHER-CENTERED INSTRUCTION
18.1 THE PARTICLE NATURE OF LIGHT AND EARLY QUANTUM THEORY
 Classical physics, Maxwell, electromagnetic radiation, universal wave equation
 Universal Wave Equation (c = f λ) and Planck’s equation (E = hf ) and kinetic energy
(EK= ½mv2)
 Atomic theory and ionization energy
2. CLASS TWO
A. TEACHER-CENTERED INSTRUCTION
INTRODUCTION OF THE PHOTOELECTRIC EFFECT (in the simplest of terms)
B. LARGE GROUP PRACTICE / DISCOVERY LEARNING (using Photoelectric Effect Simulation)
LAB 1: RELATING FREQUENCY AND INTENSITY TO CURRENT
3. CLASS THREE
A. GROUP DISCUSSION OF RESULTS:LAB 1: RELATING FREQUENCY AND INTENSITY TO CURRENT
B. TEACHER-CENTERED INSTRUCTION
THE EFFECTS OF LIGHT INTENSITY AND FREQUENCY
C. TEACHER-CENTERED INSTRUCTION
THE EXPERIMENTAL WORK OF LENARD AND THE CONCEPT OF STOPPING POTENTIAL
B. CLASS THREE
A. SMALL GROUP PRACTICE / DISCOVERY LEARNING (using Photoelectric Effect Simulation)
LAB 2: DETERMINING STOPPING POTENTIAL
B. HOMEWORK ASSIGNMENT
 Construct a graph of Stopping Potential versus Frequency (use graphing calculators
or Data Studio – Enter Data)
o
Determine the slope of the line of best fit in V∙s and in J∙s (1 eV = 1.6× 10−19 J)
o
Determine the x-intercept and the y-intercept (include range of uncertainty)
C. CLASS FOUR
A. GROUP DISCUSSION OF RESULTS FROM LAB 2: DETERMINING STOPPING POTENTIAL
B. TEACHER-CENTERED INSTRUCTION
EINSTEIN, MILLIKAN, WORK FUNCTION AND THRESHOLD FREQUENCY
D. CLASS FIVE
A. INDIVIDUAL DATA COLLECTION AND MATHEMATICAL AND GRAPHICAL ANALYSIS OF RESULTS
LAB 3A: DETERMINATION OF WORK FUNCTION AND THRESHOLD FREQUENCY FOR A SPECIFIC
METAL USING STOPPING POTENTIAL
 Set METAL to the selected metal (randomly or specifically selected by student or
instructor)
 Determine the stopping potential for 5 frequencies that include the wide range of the
available spectrum
 Record all observations.
 Plot a graph of stopping potential (V) versus frequency of incident light (Hz)
o
Determine the slope of the line of best fit in V∙s and in J∙s (1 eV = 1.6× 10−19 J)
o
Determine the x-intercept and the y-intercept (include range of uncertainty)
Compare your calculated values for work function and threshold frequency with accepted
values (using text p. 853 or on-line: Pulse Power or Hyper Physics )
B. REINFORCEMENT ACTIVITY
LAB 3B: VERIFICATION OF THE WORK FUNCTION OF A METAL FROM SIMULATION DATA USING
CRITICAL FREQUENCY
 Determine the critical frequency for a metal by changing the wavelength of incident light
at 100% intensity while the voltage is zero.
 Use the formula W = h f0 to determine the experimental value of the work function of the
metal
 Compare the two experimental values with the accepted value (text or on-line source)
 Evaluate the accuracy and effectiveness of the experiment.
C. INDIVIDUAL CONCLUDING ACTIVITY
LAB 4: IDENTIFICATION OF AN UNKNOWN METAL BY FROM ITS WORK FUNCTION AND
THRESHOLD FREQUENCY
 Determine the critical frequency for the unknown metal.
 Use the formula W = h f0 to determine the experimental value of the work function of the
metal
 Compare the experimental value with the accepted value (in text or on-line source)
 Conclude the identity of the unknown metal with supporting arguments Identify the metal
from a list of accepted work function values (in text book or on-line source)
Student products
expected
MiniLab 1: RELATING FREQUENCY AND INTENSITY TO CURRENT
MiniLab 2: DETERMINING STOPPING POTENTIAL
MiniLab 3A: DETERMINATION OF W ORK FUNCTION AND THRESHOLD FREQUENCY FOR A
SPECIFIC METAL
Lab 3B: VERIFICATION OF THE W ORK FUNCTION OF A METAL FROM SIMULATION DATA
Lab 4: IDENTIFICATION OF AN UNKNOWN METAL BY FROM ITS W ORK FUNCTION AND
THRESHOLD FREQUENCY
Samples (include
teacher notes,
assessment
information, student
work if available)
SAMPLE DATA AND GRAPH
Logistics
(organization,
grouping,
management issues,
access to
technology)

Computers with Internet and ActiveX
o Ensure at least one working computer for every two students
o Wireless laptops are preferred (Computer on Wheels)

Data projector to demonstrate basic simulation functions with whole group

Provide immediate (next class) feedback on expected relationships between variables
Assessment
information (e.g.,
rubrics for products
and/or process)
Graph of Stopping Potential versus Frequency for Sodium Metal
 created using the Enter Data option from Data Studio
 line of best fit using the Fit – Linear Fit tool
ASSESSMENT RUBRICS
MiniLab 3A: Determination of Work Function and Threshold Frequency for a Specific Metal
Lab 3B: Verification of the Work Function of a Metal from Simulation Data
Lab 4: Identification of an Unknown Metal by from its Work Function and Threshold Frequency
QUIZ
Possible extensions
Adaptations for
students requiring
additional support
Photoelectric Effect – multiple choice quiz
Applications of the Photoelectric Effect – Charge Coupling Devices (CCDs)
http://web2.uwindsor.ca/courses/physics/high_schools/2005/Photoelectric_effect/applications.html
http://www.teachnet.ie/dkeenahan/2005/page31.html
http://www.physics.rutgers.edu/ugrad/labs/photoelectric.html
APPENDICES
SIMULATION EXPERIMENTS
MiniLab 1: Relating Frequency and Intensity to Current
student worksheet
MiniLab 2: Determining Stopping Potential
student worksheet
Figure 1: Graph of Stopping Potential versus Frequency for Sodium Metal
jpg of sample data using Data Studio
MiniLab 3A: Determination of Work Function and Threshold Frequency for a Specific Metal
marking rubric
Lab 3B: Verification of the Work Function of a Metal from Simulation Data
marking rubric
Lab 4: Identification of an Unknown Metal by from its Work Function and Threshold Frequency
marking rubric
NOTES
Introduction of the Photoelectric Effect
Class 1
The Effects of Light Intensity and Frequency
Class 2
The Experimental Work of Lenard and the Concept of Stopping Potential
Class 2
Einstein, Millikan, Work Function and Threshold Frequency
Class 4
QUIZ
Photoelectric Effect
Multiple Choice Quiz
SIMULATION LAB 1: RELATING FREQUENCY AND INTENSITY TO CURRENT
Instructions

In Internet Explorer, go to phet.colorado.edu then
and
select
OR
http://phet.colorado.edu/new/simulations/sims.php?sim=Photoelectric_Effect

In the Photoelectric Effect Simulation
 Set METAL = Sodium and VOLTAGE = 0 V
 Select wavelengths that include the full range of the available spectrum (200 nm, 300 nm, 400 nm, 500 nm, 600 nm, and 700
nm)
 Convert wavelength to frequency using f = c / λ . Remember that 200 nm = 2 × 10-9 m and c = 3.0 × 108 m/s.
 For each wavelength, start with the Intensity at 0% and slowly increase the Intensity to 100%.
 Record all observations on data sheet (see over)
 Answer the concluding questions below, play some more with the simulation and record any other findings or conclusions
 State the relationship between Current and Intensity and predict the shape of the graph of the relationship.
Current (A)
Conclusions
 State the relationship between Current and Wavelength and predict the shape of the graph of the relationship.
Current (A)
Intensity (%)
Wavelength (nm)
Raw Data
Table 1.
Effect of changing the intensity of different wavelengths of light on the photoelectrons of sodium metal
and the resulting current when the voltage is zero.
Sodium Metal
Wavelength
(nm)
Frequency
(x 1015 Hz)
Colour
Minimum Intensity for
Photoelectrons (%)
200
300
400
500
600
700
Sample calculation for frequency from wavelength (use 200 nm).
Other Findings / Conclusions:
Effect of Increasing Intensity
Frequency of
Speed of
Maximum Current
Photoelectron
Photoelectrons
(A)
Emission
SIMULATION LAB 2: DETERMINING STOPPING POTENTIAL
Instructions

In Internet Explorer, go to phet.colorado.edu then
and
select
OR
http://phet.colorado.edu/new/simulations/sims.php?sim=Photoelectric_Effect

In the Photoelectric Effect Simulation
 Set METAL = Sodium
Use the same frequencies (wavelengths) from LAB 1: RELATING FREQUENCY AND INTENSITY TO CURRENT
 Set the Intensity to 50%
 For each frequency, slowly change the voltage until the most energetic photoelectrons barely do NOT reach the receiver plate
 At that “stopping potential” change the intensity.
 Record all observations in Table 2 (see reverse).
 At the stopping potential,
 State the relationship between Stopping Potential and Frequency and predict the shape of the graph of the relationship.
 State and explain any significant observations
 Answer the concluding questions below, play some more with the simulation and record any other findings or conclusions
Conclusions
State the relationship between Stopping Potential and Wavelength and predict the shape of the graph of the relationship.

State the effect of Intensity on Stopping Potential
Stopping Potential (V)
O

Wavelength (nm)
Raw Data
Table 2.
Determination of the stopping potential of sodium metal by changing the voltage for different wavelengths of light
at 50% intensity. The stopping potential is the voltage at which the current changes to 0.
Sodium Metal
Wavelength
(nm)
200
300
400
500
600
700
Other Findings / Conclusions:
Frequency
(x 1015 Hz)
Colour
Stopping Potential
(V)
GRAPH OF STOPPING POTENTIAL VERSUS FREQUENCY FOR SODIUM METAL
Lab 3 : DETERMINATION AND VERIFICATION OF WORK FUNCTION AND THRESHOLD FREQUENCY FOR A SPECIFIC METAL
Teacher Name: :
_________________________________
Student Name:
______________________________________
CATEGORY
4
3
2
1
Critical Frequency
Within 5% of accepted
value
Within 10% of accepted
value
Wavelength is accurate
(<10% error) but not
converted to frequency
No critical wavelength
found or inaccurate (>10%
error)
Work Function from Critical
Frequency
calculated correctly with
appropriate units and
significant figures
minor errors in calculations
or significant figures
significant calculation
errors OR inappropriate
units
No work function calculated
Shows wavelength,
Clearly shows wavelength,
calculated frequency and
calculated frequency and
stopping potential with
stopping potential with
units not shown or not in a
units in a logical order
logical order
Shows wavelength,
frequency and stopping
potential without sample
calculation of frequency
Shows wavelength and
frequency and stopping
potential
Data Table
Graph of Work Function
versus Frequency
Complete and accurate
with slope, x, and y
intercepts clearly labeled
Accurate but incomplete
with some labels or values
missing or unclear
Complete and some
inaccuracy of values
Incomplete labels or many
inaccurate values
Critical Frequency and
Work Function
Clearly states both values
with appropriate units and
significant figures
Clearly states both values
with inappropriate units or
significant figures
States only one value
appropriately
Neither value stated
Comparison with Accepted
Value
Experiment Evaluation
Accepted value clearly
Accepted value and source
identified and percent error Accepted value identified
clearly identified and
stated but source or
but percent error not found
percent error found
calculation not shown
Clearly evaluates the
Evaluation the accuracy
accuracy and effectiveness
and effectiveness without
with valid support
valid support statements
statements
TOTAL SCORE: ____ / 28
Either the accuracy or
effectiveness was not
evaluated or lacked
support statements
Accepted value not
identified
No valid evaluation of
accuracy nor effectiveness
Lab 4 : IDENTIFICATION OF AN UNKNOWN METAL BY FROM ITS WORK FUNCTION AND THRESHOLD FREQUENCY
Teacher Name: :
Student Name:
________________________________________
________________________________________
CATEGORY
4
3
2
1
Critical Frequency
Within 5% of accepted
value
Within 10% of accepted
value
Wavelength is accurate
(<10% error) but not
converted to frequency
No critical wavelength
found or inaccurate (>10%
error)
Work Function from Critical
Frequency
calculated correctly with
appropriate units and
significant figures
minor errors in calculations
or significant figures
significant calculation
errors OR inappropriate
units
No work function calculated
Shows wavelength,
Clearly shows wavelength,
calculated frequency and
calculated frequency and
stopping potential with
stopping potential with
units not shown or not in a
units in a logical order
logical order
Shows wavelength,
frequency and stopping
potential without sample
calculation of frequency
Shows wavelength and
frequency and stopping
potential
Data Table
Graph of Work Function
versus Frequency
Complete and accurate
with slope, x, and y
intercepts clearly labeled
Accurate but incomplete
with some labels or values
missing or unclear
Complete and some
inaccuracy of values
Incomplete labels or many
inaccurate values
Critical Frequency and
Work Function
Clearly states both values
with appropriate units and
significant figures
Clearly states both values
with inappropriate units or
significant figures
States only one value
appropriately
Neither value stated
Comparison with Possible
Accepted Values
Three most probable
metals with accepted
values and source clearly
identified
One possible metal with
Two most probable metals
accepted values and
with accepted values and source clearly identified or
source clearly identified
two probable metals
without source
Identity of Unknown Metal
Correct identification of
Correct identification of
unknown with valid reasons unknown without reasons
TOTAL SCORE: ____ / 28
Incorrect identification of
unknown but valid reasons
No possible metals with
sources identified
Incorrect identification of
unknown without valid
reasons
NOTES
UNIT 7 WAVES AND MODERN PHYSICS
Chapter 18
Classical Physics
Early Quantum Theory
the laws, theories, and explanations about mechanics, thermodynamics, electricity
and magnetism prior to 1900.
− explains most of the observations in our lives
− fails to explain the photelectric effect and ultraviolet radiation by a blackbody
James Clerk MAXWELL − Electromagnetic Waves
 Changing electric fields induce changing magnetic fields.
 Changing magnetic fields induce changing electric fields.
 Together, the alternating electric and magnetic fields radiate from the source into space.
 The frequency of the waves is determined by the frequency of either the magnetic field or the electric field that
produced the waves.
Electromagnetic Radiation
Types
Energy carried by electromagnetic waves through space
All electromagnetic radiation moves at the speed of light, c
Radio waves, microwaves, infrared (heat), visible light, ultraviolet light,
X-rays, gamma rays, cosmic rays
Universal Wave Equation
Wavelength (λ) and frequency (f) of the waves are related by the speed of light (c)
c=fλ
Frequency varies inversely with wavelength.
18.1 The Particle Nature of Light
BLACKBODY RADIATION
Blackbody
An object that absorbs all frequencies of light (= black)
An object that emits a complete, continuous spectrum of electromagnetic radiation
When an object is heated a little and turns red, it emits infrared (IR) radiation.
When the object is heated until it glows white, it emits visible light (ROYGBIV).
Kirchhoff
Boltzmann
All objects absorb the same frequencies of radiation that they emit
 demonstrated that the power radiated by a blackbody varies with its temperature.
 used Maxwell’s idea of emission of radiation by vibrating charges on the surface to a blackbody
 predicted that the energy radiated from a blackbody increased as the frequency increased
o true for low energy (infrared and visible) emissions
Ultraviolet Catastrophe the huge difference between the predicted energy and the actual energy
emitted by higher frequencies of radiation
The experimental observations could not be explained by classical physics
840
EARLY QUANTUM THEORY
843
Electrons are believed to move about the nucleus of an atom on discrete energy levels (shells).
Electrons can absorb the energy of electromagnetic radiation. If enough energy is absorbed, they jump to a higher energy level
(excited state).
Eventually, the electrons release energy and return to their starting (ground state) energy level. The energy is released as a
packet electromagnetic radiation called a photon.
Max Planck
German physicist who first realized that the energy released by excited electrons only comes in packets of
specific sizes with certain frequencies.
E=nhf
, where n = energy level  integer values only (0, 1, 2, 3,…)
h = Planck’s constant 6.626 x 10–34 J / Hz
f = frequency (Hertz)
INTRODUCTION OF THE PHOTOELECTRIC EFFECT
844
Electrons (photoelectrons) escape from the surface of a metal when light is shone on the metal.
The photoelectrons are detected by an ammeter when they strike a metal plate that allows the circuit to
be completed.
Photoelectric Effect – the emission of electrons from a metal when exposed to electromagnetic radiation.
Photoelectric cells use these photoelectrons in a closed circuit.
Plants use the photoelectrons in the process of photosynthesis
Garage door openers and solar panels operate using photoelectrons
Heinrich Hertz
discovered the photoelectric effect by accident when sparks jumped between
across a separate circuit when a nearby oscillating current
Led to development of radio, tv, microwave communication (Wii), and radar
THE EFFECTS OF LIGHT INTENSITY AND FREQUENCY
845
Light Intensity only affects the rate that photoelectrons are released (photoelectrons released per
second) and does not affect the speed (maximum kinetic energy) of the photoelectrons.
Light Frequency determines the amount of energy that can be transferred to each electron (E=hf) which
directly affects the kinetic energy (speed) of the photoelectron.
THE EXPERIMENTAL WORK OF LENARD AND THE CONCEPT OF STOPPING POTENTIAL
846
Philipp Lenard controlled the potential differences between the incident metal plate and the detector
plate.
Stopping Potential is the potential difference that will stop all photoelectrons from reaching the detector
plate.
EINSTEIN, MILLIKAN, WORK FUNCTION AND THRESHOLD FREQUENCY
P 847-853
Einstein

light behaves as packets of energy called photons

the intensity of light affects the number of photons, not the energy of each photon

the energy of one photon (E = hf) is transferred to one electron in one event
o
higher frequency photons (UV radiation) has more energy than IR photons

some of the energy transferred is used to do work to overcome the attractive forces in the substance
and the remainder was converted to kinetic energy

more work is needed for electrons further beneath the surface than those on the surface
Work Function – minimum amount of energy required to remove an electron from the surface of a metal
(W)
Each metal has a distinct work function
Maximum Kinetic Energy of a photoelectron is achieved when a surface electron is removed.
(EKmax)
hf = EKmax + W
Millikan

experimentally determined the charge of a single electron (qe = 1.6 × 1019C)

tried to prove Einstein wrong by precisely measuring the stopping potential for a variety of
frequencies of several metals

the maximum kinetic energy must be less than or equal to the electrical potential energy
EKmax ≤ EP= qe∙Vs

plotted maximum kinetic energy versus frequency
EKmax = hf – W
compare to y = mx + b


slope = h = Planck’s constant

y-intercept (b) = −W = negative work function

x-intercept (a) = f0 = threshold (critical) frequency
provided experimental support of Einstein’s proposals of the quantum nature of the photoelectric
effect
Threshold Frequency (f0) the minimum frequency of the radiation (photon) required for a certain metal
to emit a photoelectron.
Einstein’s Photon Theory the excess energy of the incoming photon becomes the kinetic energy of the
emitted electron.
Ek = h f - h f0
where h f is the energy of the incoming photon and
h f0 is the minimum energy required to escape
(h f0 = W)
MEASURING KINETIC ENERGY OF PHOTOELECTRONS IN ELECTRON VOLTS
850
The energy of the photoelectron is measured by balancing its kinetic energy with the repulsive force of a
negatively charged anode.
The respulsive force depends on the voltage at the anode (stopping potential).
EK = – q V0
where EK = the maximum kinetic energy of the electron
q = the charge on the electron
qe– = –1.60 x 10–19 C
V0 = the stopping potential of the anode
The kinetic energy of an electron is very small, so electron volts (eV) are used instead of joules.
One electron volt is the energy of one electron accelerated against a potential difference of one volt.
1 eV = 1.60 x 10–19 J
Practice Problems (p. 561) 3, 4
Quiz: Photoelectric Effect
_____ 1.
_____ 2.
_____ 3.
_____ 4.
_____ 5.
Physics 12
Name: ___________________
What is the term used to refer to the minimum energy required for a photoelectron to
escape from a metal plate in a photocell?
A.
stopping voltage
B.
Planck’s constant
C.
threshold wavelength
D.
work function
Threshold frequency is to work function as hertz is to which one of the following?
A.
coulomb
B.
joule
C.
newton
D.
watt
The variable that varies directly with the amount of current produced by photoelectrons
A.
the intensity of the incident light
B.
the frequency of the incident light
C.
the wavelength of the incident light
D.
the work function of the metal surface
The threshold frequency has a value of X. If the frequency of the incident light increases
from 2X to 4X, then the resulting current of photoelectrons
A.
is doubled
B.
is increased by a factor or 3
C.
reduced by half
D.
remains the same
When electromagnetic radiation with a wavelength of 350 nm falls on a metal, the
maximum kinetic energy of the ejected electrons is 1.20 eV. What is the work function of
the metal?
A.
1.3 eV
B.
2.4 eV
C.
5.4 eV
D.
5.7 eV
_____ 6.
A.
210 nm
B.
420 nm
C.
530 nm
D.
620 nm
The graph below shows the relationship between the frequency of radiation incident on a
photosensitive surface and the maximum kinetic energy of the emitted photoelectrons.
Kinetic Energy (eV)
_____ 7.
Calculate the wavelength of a photon with 3.2 × 10–19 J of energy.
P
Frequency (Hz)
What does point P represent?
_____ 8.
A.
fundamental frequency
B.
photoelectron frequency
C.
photon escape frequency
D.
threshold frequency
The work function of a particular photo-emissive material is 4.0 eV. If photons with 16 eV
of energy are incident on the material, what would be the maximum kinetic energy of the
ejected photoelectrons?
A.
0.25 eV
B.
4.0 eV
C.
12 eV
D.
20. eV