Chapter 9 Momentum Chapter 10 Electrostatics Chapter 11 Electric Fields Chapter 12 Magnetic Fields Chapter 13 Lights Waves Chapter 14 Light Duality Chapter 15 Atomic Chapter 16 Radiation Chapter 17 Quarks

Unit 7: Forces and Fields

Unit Themes and Emphases

Focussing Questions

Unit C: Electromagnetic Radiation

Themes: Diversity and Matter
Overview: In this unit, students study the nature and characteristics of electromagnetic radiation (EMR), using the wave and photon models of light.
This unit builds on:
  • Science 8, Unit C: Light and Optical Systems
  • Physics 20, Unit C: Circular Motion, Work and Energy
  • Physics 30, Unit A: Momentum and Impulse and Unit B: Forces and Fields
This unit prepares students for further study of EMR phenomena and the nature of matter in Unit D and for post-secondary studies in physics. Unit C will require approximately 30% of the time allotted for Physics 30.

Focusing Questions:
  • What roles do electricity and magnetism play in EMR?
  • Does EMR have a wave or a particle nature?
  • What experimental evidence is required to decide whether EMR has a wave or a particle nature?
  • What technological devices are used today as a result of investigating and applying electromagnetic phenomena?
General Outcomes: There are two major outcomes in this unit.
Students will:
  1. explain the nature and behaviour of EMR, using the wave model
  2. explain the photoelectric effect, using the quantum model.
Key Concepts: The following concepts are developed in this unit and may also be addressed in other units or in other courses. The intended level and scope of treatment is defined by the learning outcomes.
  • speed of EMR
  • propagation of EMR
  • reflection
  • refraction
  • diffraction
  • interference
  • total internal reflection
  • Snell’s law
  • photoelectric effect
  • Compton effect
General Outcome

C1 Students will explain the nature and behaviour of EMR, using the wave model.

Specific Outcomes for Knowledge
Students will:

30–C1.1k describe, qualitatively, how all accelerating charges produce EMR

30–C1.2k compare and contrast the constituents of the electromagnetic spectrum on the basis of frequency and wavelength

30–C1.3k explain the propagation of EMR in terms of perpendicular electric and magnetic fields that are varying with time and travelling away from their source at the speed of light

30–C1.4k explain, qualitatively, various methods of measuring the speed of EMR

30–C1.5k calculate the speed of EMR, given data from a Michelson-type experiment

30–C1.6k describe, quantitatively, the phenomena of reflection and refraction, including total internal reflection

30–C1.7k describe, quantitatively, simple optical systems, consisting of only one component, for both lenses and curved mirrors

30–C1.8k describe, qualitatively, diffraction, interference and polarization

30–C1.9k describe, qualitatively, how the results of Young’s double-slit experiment support the wave model of light

30–C1.10k solve double-slit and diffraction grating problems using:

λ =   Δxd        this equation works in all cases  
nl
λ =   d × sin θ        this equation only works for small angles, θ < 100
n

30–C1.11k describe, qualitatively and quantitatively, how refraction supports the wave model of EMR, using:

sin θ1  =  n2  =  v1  =  λ1
sin θ2 n θ1 v2 λ2

30–C1.12k compare and contrast the visible spectra produced by diffraction gratings and triangular prisms.



Specific Outcomes for Science, Technology and Society (STS) (Nature of Science Emphasis)
Students will:

30–C1.1sts explain that scientific knowledge is subject to change as new evidence becomes apparent and as laws and theories are tested and subsequently revised, reinforced or rejected (NS4)

  • use examples, such as Poisson’s spot, speed of light in water, sunglasses, photography and liquid crystal diodes, to illustrate how theories evolve

30–C1.2sts explain that scientific knowledge may lead to the development of new technologies, and new technologies may lead to or facilitate scientific discovery (ST4) [ICT F2–4.4]

  • describe procedures for measuring the speed of EMR
  • investigate the design of greenhouses, cameras, telescopes, solar collectors and fibre optics
  • investigate the effects of frequency and wavelength on the growth of plants
  • investigate the use of interferometry techniques in the search for extrasolar planets.
Note: Some of the outcomes are supported by examples. The examples are written in italics and do not form part of the required program but are provided as an illustration of how the outcomes might be developed.


Specific Outcomes for Skills (Nature of Science Emphasis)

Initiating and Planning
Students will:

30–C1.1s formulate questions about observed relationships and plan investigations of questions, ideas, problems and issues

  • predict the conditions required for diffraction to be observed (IP–NS3)
  • predict the conditions required for total internal reflection to occur (IP–NS3)
  • design an experiment to measure the speed of light (IP–NS2).

Performing and Recording Students will:

30–C1.2s conduct investigations into relationships among observable variables and use a broad range of tools and techniques to gather and record data and information

  • perform experiments to demonstrate refraction at plane and uniformly curved surfaces (PR–NS2)
  • perform an experiment to determine the index of refraction of several different substances (PR–NS2, PR–NS3, PR–NS4)
  • conduct an investigation to determine the focal length of a thin lens and of a curved mirror (PR–NS2, PR–NS3, PR–NS4)
  • observe the visible spectra formed by diffraction gratings and triangular prisms (PR–NS2)
  • perform an experiment to determine the wavelength of a light source in air or in a liquid, using a double-slit or a diffraction grating (PR–NS2, PR–NS3)
  • perform an experiment to verify the effects on an interference pattern due to changes in wavelength, slit separation and/or screen distance (PR–NS2, PR–NS3) [ICT C7–4.2].

Analyzing and Interpreting
Students will:

30–C1.3s analyze data and apply mathematical and conceptual models to develop and assess possible solutions

  • derive the mathematical representation of the law of refraction from experimental data (AI–NS2) [ICT C7–4.2]
  • use ray diagrams to describe an image formed by thin lenses and curved mirrors (AI–NS1)
  • demonstrate the relationship among wavelength, slit separation and screen distance, using empirical data and algorithms (AI–NS6)
  • determine the wavelength of EMR, using data provided from demonstrations and other sources; e.g., wavelengths of microwaves from the interference patterns of television signals or microwave ovens (AI–NS3, AI–NS4).

Communication and Teamwork
Students will:

30–C1.4s work collaboratively in addressing problems and apply the skills and conventions of science in communicating information and ideas and in assessing results

  • select and use appropriate numeric, symbolic, graphical and linguistic modes of representation to communicate findings and conclusions; e.g., draw ray diagrams (CT–NS2).
Note: Some of the outcomes are supported by examples. The examples are written in italics and do not form part of the required program but are provided as an illustration of how the outcomes might be developed.


General Outcome 2

C2 Students will explain the photoelectric effect, using the quantum model.

Specific Outcomes for Knowledge
Students will:

30–C2.1k define the photon as a quantum of EMR and calculate its energy

30–C2.2k classify the regions of the electromagnetic spectrum by photon energy

30–C2.3k describe the photoelectric effect in terms of the intensity and wavelength or frequency of the incident light and surface material

30–C2.4k describe, quantitatively, photoelectric emission, using concepts related to the conservation of energy

30–C2.5k describe the photoelectric effect as a phenomenon that supports the notion of the wave-particle duality of EMR

30–C2.6k explain, qualitatively and quantitatively, the Compton effect as another example of wave-particle duality, applying the laws of mechanics and of conservation of momentum and energy to photons.


Specific Outcomes for Science, Technology and Society (STS) (Nature of Science Emphasis)
Students will:

30–C2.1sts explain that scientific knowledge and theories develop through hypotheses, the collection of evidence, investigation and the ability to provide explanations (NS2)

  • describe how Hertz discovered the photoelectric effect while investigating electromagnetic waves
  • describe how Planck used energy quantization to explain blackbody radiation

30–C2.2sts explain that concepts, models and theories are often used in interpreting and explaining observations and in predicting future observations (NS6a)

  • investigate and report on the development of early quantum theory
  • identify similarities between physicists’ efforts at unifying theories and holistic Aboriginal worldviews

30–C2.3sts explain that the goal of technology is to provide solutions to practical problems (ST1) [ICT F2–4.4]

  • analyze, in general terms, the functioning of various technological applications of photons to solve practical problems; e.g., automatic door openers, burglar alarms, light meters, smoke detectors, X-ray examination of welds, crystal structure analysis.


Specific Outcomes for Skills (Nature of Science Emphasis)
Initiating and Planning
Students will:

30–C2.1s formulate questions about observed relationships and plan investigations of questions, ideas, problems and issues

  • predict the effect, on photoelectric emissions, of changing the intensity and/or frequency of the incident radiation or material of the photocathode (IP–NS3)
  • design an experiment to measure Planck’s constant, using either a photovoltaic cell or a light-emitting diode (LED) (IP–NS2, IP–NS4).
Performing and Recording
Students will:

30–C2.2s conduct investigations into relationships among observable variables and use a broad range of tools and techniques to gather and record data and information

  • perform an experiment to demonstrate the photoelectric effect (PR–NS3) [ICT C6–4.4]
  • measure Planck’s constant, using either a photovoltaic cell or an LED (PR–NS2, PR–NS3).
Analyzing and Interpreting
Students will:

30–C2.3s analyze data and apply mathematical and conceptual models to develop and assess possible solutions

  • analyze and interpret empirical data from an experiment on the photoelectric effect, using a graph that is either drawn by hand or is computer generated (AI–NS2, AI–NS4) [ICT C6–4.2, C6–4.3].
Communication and Teamwork
Students will:

30–C2.4s work collaboratively in addressing problems and apply the skills and conventions of science in communicating information and ideas and in assessing results

  • select and use appropriate numeric, symbolic, graphical and linguistic modes of representation to communicate findings and conclusions (CT–NS2).
Links to Mathematics
The following mathematics outcomes are related to the content of Unit C but are not considered prerequisites.
 Concept  Mathematics Course, Strand and Specific Outcome
 Data Collection and Analysis  Grade 9 Mathematics, Statistics and Probability (Data Analysis), Specific Outcome 3
 Measurement and Unit Conversions  Mathematics 10C, Measurement, Specific Outcomes 1 and 2;
 Mathematics 10-3, Measurement, Specific Outcome 1;
 Mathematics 20-3, Algebra, Specific Outcome 3
 Trigonometry  Mathematics 10C, Measurement, Specific Outcome 4;
 Mathematics 10-3, Geometry, Specific Outcomes 2 and 4
 Rate and Proportions  Mathematics 20-2, Measurement, Specific Outcome 1
 Graph Analysis  Mathematics10C, Relations and Functions, Specific Outcomes 1, 4 and 7;
 Mathematics 20-3, Statistics, Specific Outcome 1
 Mathematics 30-1, Relations and Functions, Specific Outcome 14
 Mathematics 30-1, Trigonometry, Specific Outcome 4; Mathematics 30-2, Relations and Functions, Specific Outcome 8
 Solving Equations  Mathematics 20-1, Algebra and Number, Specific Outcome 6;
 Mathematics 30-2, Relations and Functions, Specific Outcome 3
 Scale Diagrams  Mathematics 20-2, Measurement, Specific Outcome 2;
 Mathematics 20-3, Geometry, Specific Outcome 2
 Slope  Mathematics10C, Relations and Functions, Specific Outcomes 3 and 5;
 Mathematics 20-3, Algebra, Specific Outcome 2
 Powers  Mathematics10C, Algebra and Number, Specific Outcome 3




Chapter 14: The wave-particle duality reminds us that sometimes truth really is stranger than fiction!

Key Concepts

  • the idea of the quantum
  • the wave–particle duality
  • basic concepts of quantum theory

Knowledge

  • describe light using the photon model
  • explain the ways in which light exhibits both wave and particle properties
  • state and use Planck’s formula
  • give evidence for the wave nature of matter
  • use de Broglie’s relation for matter waves

Science, Technology, and Society

  • explain the use of concepts, models, and theories
  • explain the link between scientific knowledge and new technologies

Flippity Review Questions for Chapter 14

Flippity Review QR Code

 




14.1 The Birth of the Quantum

Black body radiation
Dark metal objects were observed to release visible light EMR when heated. As the temperature increased, the frequency of the EMR increased.
Ie. The metal releases IR, then red, orange, white then UV radiation as the temperature increases.
Scientists expected this to continue. They hypothesized that as the temperature increased the frequency of the emitted emr would continue to increase to X-rays, gamma and cosmic rays.
In reality the emitted emr stopped increasing in the UV part of the spectrum.
This was called the ultraviolet catastrophe because the theory did not work for UV light.
In 1900 Max Planck suggested that light could only exchange specific wavelengths of light with its surroundings.
Quantum was the name given to the smallest amount of energy of a particular wavelength or frequency.

E =   hf   =   hc
λ

The quantum theory of light is the wave-particle duality, where light behaves like a wave (shown by Young interference and Snell refraction) and a particle (Hertz and Einstein photoelectric effect)



 


14.2 The Photoelectric Effect

Heinrich Hertz continued to work with EMR and electric charges after he proved Maxwell was correct.
He found that his spark gap worked much better when a UV light was shone on the gap.
He also found that if he shone a UV light on a charged plate, the plate would lose its charge.
Hertz’ discovery led to shining difference frequency light on metals and looking at charge.
The photoelectric effect is when light above a threshold frequency (fo) is shone on a piece of metal, a potential difference is created across the metal by the light.
This is how solar cells create current.
Millikan calculated the value for Planck’s constant by using Hertz’ discovery.
The Photoelectric effects is when photons of light transfer their energy to electrons removing from the atom and making them flow as an electric current (photoelectrons).
To measure the energy they used a retarding voltage to slow down electrons, which was a stopping voltage when the current (electrons) stopped flowing. The stopping voltage is equal to the kinetic energy of the photoelectrons.
Ek = hf - W Ek = hf – W
Y = mx + b
If you graph the frequency of the incident light vs the kinetic energy of the photoelectrons we get


 


14.3 The Compton Effect

Arthur Compton used X-rays to penetrate a block of graphite (carbon) and examine the crystal configuration.
He noticed that the frequency of the X-ray decreased as it went through graphite. This violated the law of conservation of energy, so he started looking at the energy in more detail.
Compton discovered that energy was lost to ejecting electrons from the block of graphite.
Compton noticed that it looked like a conservation of momentum calculation. He was able to use this to show that photons of EMR have momentum.

p =   h
λ

The scattering angle is calculated by

Δλ =   hc (1-cosθ)
λ

Compton’s work was revolutionary because it proved that energy, EMR, could have momentum which is a matter property.


 


14.4 Matter Waves and the Power of Symmetric Thinking

Wave particle duality of EMR states that EMR behaves like a wave of energy and it will behave like a particle of matter. Louis de Broglie thought that if light behaves like a wave and particle, maybe matter can behave like a wave. He used momentum to show the wavelength of matter.
deBroglie was shown to be correct by firing a stream of electrons at a salt crystal and looking at the interference pattern created.
deBroglie showed that microscopic (sub-atomic) matter moves in waves, not linearly. This also allows us to calculate the frequency of the matter.
For human sized matter the wavelength is so small as to be irrelevant.


 


14.5 Coming to Terms with Wave-Particle Duality and the Birth of Quantum Mechanics

Quantum mechanics is governed by probabilities and statistics. “Weird” things happen.
Eg. A single photon will interfere with itself to make Young’s double slit experiment work.
Eg. An electron will travel from point A to B without ever being in between.


 
Program of Studies
Alberta Science 10
Program of Studies
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Contact me:

Steven Montgomery

steven.montgomery@pembinahills.ca

BCHS Barrhead AB
Textbook
Physics 20 & 20 Textbook (2009)
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