The Duality of Light
| Topic | Waves and the Particle/Wave Theory of Light |
|---|---|
| Program | Brown Science Prep |
| Developed by | Mark Sabbagh |
| Developer Type | Undergraduate students |
Overview / Purpose / Essential Questions
- What
is energy?
- How
can it manifest itself?
- What
is a wave?
- How
do we know light is both a wave and a particle?
- How
can waves/light transform energy?
- Matter
(mass) is energy.
- How
does the duality of light reflect a change in scientific thinking?
Performance / Lesson Objective(s)
The goal of this lessons is to have students fully understand what energy as a concept, and how it manifests itself physically. At the same time, the lesson aims at detailing the scientific mode of thinking through the question of what exactly light is.
Lesson Materials
Smoke Ring Cannon
Ripple Tank
Lesson Motivation
Energy is an extremely important concept to all fields of science and having a firm grasp of the idea will allow students to understand many real world phenomena better. Also, the duality of light is a great metaphor for what scientists quest to understand and how sometimes the answers we get provide further questions.
Lesson Activities
Smoke ring cannon demonstration, ripple tank activity to show different wave properties, and demonstration of a light diffraction pattern.
Procedure
Open demonstration:
Smoke Ring Cannon, technically not wave, however, a good demonstration of energy travelling through air
Begin with a discussion of energy
o Have students give their own
definitions/examples
o Energy
can be defined as the ability a physical system has to do work on another
physical system.
§ Feel
free to expand on whether energy is something abstract or concrete. Is energy a thing or an action waiting to
happen?
Discuss
mechanical waves
o During this part of the lesson, either
draw a transverse wave on the board or have two students use a piece of string
to create a wave. Refer to either when explaining
o A
wave is a disturbance that travels through space. Alternatively, they are
transferences of energy from one point to another through a medium.
§
KEY
POINT: the particles of the medium are not displaced, rather the energy is what
moves.
§
Do
some demo utilizing students as air particles and some object as energy. The
students/air assist the object/energy from going from point A to point B
o Define crest, trough, amplitude, period,
wavelength, and any other terms you see fit to discuss
·
Activity
to illustrate various properties of waves
o Basically we’re going to use water
ripples to illustrate reflection, refraction, and diffraction
o Need a ripple tank (http://en.wikipedia.org/wiki/Ripple_tank#Demonstrating_wave_properties)
o Reflection
§
Just
have a metal bar on other end
o Refraction
§
Use
sheet of glass to create shallower water
o Diffraction
§
Create
small opening
o Diffraction pattern
§
Two
small openings
§
Interference is when two waves superpose
with each other to either increase or decrease amplitude.
§
Point
out dark and light bands
·
Discuss
light
o See what students know
o Discuss particle theory of light
§
Newton
proposed light was made up of tiny particles moving in a straight line at a
certain velocity
§
These
are photons. Discrete “packets” of light.
§
Compare
to electrons. Theory developed by Albert Einstein to explain black body
radiation
·
When
you heat up a stove it glows. Why?
o Thermal energy excites the atoms of the
metal exciting electrons. These then drop back down to ground state and release
a photon.
o Feel free to discuss energy levels of
atoms.
o Discuss wave theory of light
§ Try
and not mention that light is a wave. Here can show a demonstration of the
double slit experiment showing lights diffraction pattern
o Have students try and explain the
observation.
§
Back
in groups work with students in trying to reconcile two very different
observations.
·
On
one hand we have photons which explain blackbody radiation, something a wave
theory can’t explain
·
On
the other hand we see a diffraction pattern. But we said waves need a medium.
Light can travel through a vacuum.
·
Duality of light aka wave-particle theory
o Light is both a wave and a particle.
o Electromagnetic radiation
§
Light
is a magnetic field perpendicular to an electric field that is capable of
propagating itself.
o Matter is energy. (mass is energy)
·
INTERESTING
IDEA: Light is both a wave and a particle, electromagnetic radiation and a
photon. Now the former is in essence energy itself, electromagnetic energy. The
latter is matter. Thus, matter is energy.
·
DeBroglie
hypothesizes all matter has a wavelength. How could you show matter is energy?
That all matter/particles are also waves?
o If possible get students to suggest by
showing another particle (an electron) behaves like a wave. That is produces a
diffraction. Don’t tell them, try and
get them to reach the conclusion.
o In fact electrons do produce a
diffraction pattern: still trying to find a good video
·
Change
in scientific thinking
o Originally light thought to be particles.
Then shown to be waves. Then Einstein comes up with photons. Then all matter is
thought to be both wave and particle. Small discussion of quantum mechanics,
how Einstein didn’t like it due to uncertainty involved.
o Point is like energy and the world,
scientific ideas are constantly changing. Reason it’s so great.
Wrap up / Conclusion
Ask students what they think light is.
Supporting Web Information
Wikipedia
Pre Assessment Plan
Draw a diagram of a wave and have them label parts
Post Assessment Plan
Repeat questions of pre-assessment plan
Alignment Info
| Audience(s) | High school students |
|---|---|
| STEM Area(s) | Physics |
| Standard(s) |
|
| Activity Type(s) | Hands-on Lecture |
| Grade Level(s) | High School |
| Version | 1 |
| Created | 10/02/2011 12:12 PM |
| Updated | 02/22/2012 10:46 AM |