Physics 106, Summer 2012
27 & 28 (all)
Did you complete the reading assignment?
Did you complete the entire quiz or spend at least 15
minutes working on this quiz and the attached links?
1) All particles express
wave-like behaviors; however, this phenomenon is only observable on a very
2) The energy of light
is determined by its frequency, not its intensity.
3) Specific pairs of physical properties
cannot be known simultaneously.
Quantum physics has quite possibly the most intimidating reputation of any
subject. Professor Farnsworth explains the basics of quantum physics in 16
seconds to help you realize it is not as intimidating as you may think:
That description really is not all that far off. The basic idea of quantum
physics is that there are no absolute certainties, only probabilities. In
other words, because of the nearly infinite reactions going on between the
smallest particles, we can never be 100% sure about our predictions on
anything (position, momentum, energy, etc.). This does not mean that crazy
things will happen for no reason (just that we do not always know what the
reason is), and we can predict most things within very
small ranges of error, but there is always the EXTREMELY SMALL chance that
something we do not expect could happen. These predictions that we make do
not use the classical model of physics which you have experienced and
practiced with, but need to use an entirely different model, the quantum
model. This new model is very different and seems very strange compared to
classical physics; even Albert Einstein who was known for reshaping
classical physics referred to quantum as "spooky."
Exercise 1: Wave-Particle
The theory of quantum physics is based on wave-particle duality. The
following link teaches a principle you have already learned, the double-slit
experiment, but puts it into the world of quantum:
What would you see if you shot large particles through a double-slit setup?
Two straight lines of particles spaced just like the slits are spaced.
A wave-like interference pattern with the brightest ridge at the center.
What would you see if you shot tiny particles through a double-slit setup?
Scientists can observe tiny particles using filters that will collect
electrons going through them. How would putting an electron filter next to
one of the two slits affect the behavior of the electrons?
The would behave as if they were large particles. There would be no interference pattern.
2: The Photoelectric Effect
The photoelectric effect is the effect that light has on the electrons of a
metal plate when the light is shined on the plate. Go to the following
Click the 'Electron energy vs light frequency' box on the right hand side.
Now increase and decrease the intensity of light. What affect does
increasing the intensity of light have on the energy of electrons being
knocked off of the plate?
Increases the energy
Decreases the energy
Does not affect the energy
Now increase and decrease the frequency of light. What affect does increasing
the frequency of light have
on the energy of the electrons being knocked off the plate?
It is common knowledge that the Sun's ultraviolet light is what causes
sunburns. The most intense light emitted by the sun is visible light
(between blue and green), so why are we most worried about the UV light?
Because only high energy light can damage our skin. This high energy light is the ultraviolet light becuase it has a higher frequency.
Why will you be more badly burnt by the sun at midday then at sunset?
The sunlight at midday is more intense, meaning, that there is more of the ultraviolet light that can affect your skin at the same time. The frequency of the light that damages skin is the same at both times of the day, but at midday there is more of the harmful frequency light coming in contact with your skin.
3: The Heisenberg Uncertainty Principle
"The only true wisdom is in
knowing you know nothing."- Socrates
The most famous pairing of physical quantities in the uncertainty principle
is the pairing of position and momentum. Go to the following link to see how
these pairs interact (click on the 'Load Applet' button after going to the
This applet can get very confusing very quickly if you don't know what you
are looking at. First, change the 'center' scroll bar to 0.0 and keep it
there. The only two graphs you need to worry about are the top left and top
right graphs. The top left graph represents where the particle is, the
higher the amplitude at that point, the more likely it is to be in that
position. On the other hand, the more spread out the graph is, the more
possibilities there are for the particle to be located somewhere else. The
top right graph is similar, but for momentum rather than position. The
skinnier the peak in the top right graph, the more you know about the
Change the 'width' scroll bar to the left to decrease how well you know the
momentum of the particle. Do you know more or less about the position of the
If you knew the exact position of a particle, what would you know about its
Joke of the Quiz: Chuck Norris is the
only human being to display the Heisenberg uncertainty principle — you can
never know both exactly where and how quickly he will roundhouse-kick you in
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Was there anything that you didn't understand in the reading assignment?
What was confusing to you?