Name: ________________________
Quantum Physics – Summary

What is Quantum Physics?
Quantum physics, also called quantum ____________ is the study of matter
and radiation at an ________________ level. In the early 20th century some
experiments produced results which could not be explained by classical
physics
(the
science
developed
by
__________________,
_______________, etc.). For instance, it was well known that electrons
orbited the ___________ of an atom. However, if they did so in a manner
which resembled the planets orbiting the sun, classical physics predicted
that the electrons would spiral in and crash into the nucleus within a fraction
of a second. That incorrect prediction, along with some other experiments that ______________ physics could not
explain, showed scientists that something new was needed to explain science at the atomic level. However: For
everyday things, which are much larger than atoms, classical physics does an excellent job.

Important Experiments in Quantum Physics
a) Double-Slit Experiment
If electrons or photons (or even larger particles) are used in the double-slit experiment (see
“optics”) we can observe an _______________ _____________. This shows that all particles at
an atomic scale must be considered as both a particle AND a wave. This is called _____________
- ___________ - _____________.
b) Photoelectric Effect
The photoelectric effect (nobel prize for Einstein in 1921) can only be explained if
we consider light as a stream of ___________. A metal is illuminated with light. If
this light happens to have the right ___________, it is able to set electrons free
from the metal. An electric ____________ occurs and can be measured. the photon
energy is too low, the electron is unable to escape the surface of the material. Increasing the ________________ of the
light beam does not change the energy of the incoming photons, only the their number. Thus the energy of the emitted
_____________ does not depend on the intensity of the incoming light, but only on the frequency of the photons. The
photoelectric effect is the basis for solar cells and modern light detectors.
c)
Schrödinger’s Cat
.. is a __________ experiment devised by the Austrian physicist __________
_____________.
A
cat
is
placed
in
a
box,
together
with
___________________________. If one of the atoms emits an alpha particle
(which is a random process), and the geiger-counter detects it, the hammer hits a
flask of poison, killing the cat. We then ask: Is the cat alive or dead?
The answer according to quantum mechanics is that it is 50% dead and 50% alive. Physicists and philosophers think of
the cat as being dead AND alive at the same time (superposition of two states). Only if we take a measurement and open
the box, we will get the result of a dead or alive cat, but at the same time we’ll destroy this superposition.
© Mag. Susanne Neumann – BRG XIV (susanne.neumann@brg14.at)
Name: ________________________

Laws of Quantum Physics
a) Heisenberg’s Uncertainty Principle
At the atomic scale measurement becomes a very delicate process. Let's say you want to find out
where an electron is and where it is going. How would you do it? Get a super high powered
magnifier and look for it? The very act of looking depends upon light, which is made of
photons, and these photons could have enough momentum that once they hit the electron they
would change its course! Werner Heisenberg was the first to realize that certain pairs of
measurements have an intrinsic uncertainty associated with them. For instance, if you have a very good idea of where
something is located, then, to a certain degree, you must have a poor idea of how fast it is moving or in what direction.
We don't notice this in everyday life because any inherent uncertainty from Heisenberg's principle is well within the
acceptable accuracy we desire.
b) Energy of a Photon
As light has to be considered as both a wave and a stream of photons, there has to be a relationship between the energy
of the photon and the frequency of the wave. They are directly proportional to each other with “h” (Planck’s constant =
6.6  10 34 Js ) as the constant of proportionality. The relationship can therefore be described as: _________________
??? What is the energy of a photon producing blue light (f=650 THz) ???
__________________________________________________________

Applications of Quantum Physics
Quantum mechanics has had enormous success in explaining many of the features of our world. The individual
behaviour of the subatomic particles that make up all forms of matter—electrons, protons, neutrons, photons and
others—can often only be satisfactorily described using quantum mechanics. Quantum mechanics is important for
understanding how individual atoms combine covalently to form _______________. (Relativistic) quantum mechanics
can in principle mathematically describe most of chemistry. Quantum mechanics can provide quantitative insight into
ionic and covalent bonding processes by explicitly showing which molecules are energetically favorable to which
others, and by approximately how much. Most of the calculations performed in computational chemistry rely on
quantum mechanics.
Much of modern technology operates at a scale where quantum effects are
significant. Examples include the ___________ (Light Amplification by
Stimulated Emission of Radiation), the electron microscope, and magnetic
resonance imaging. The study of semiconductors led to the invention of the
___________ and the _________________, which are indispensable for modern electronics.
Researchers are currently seeking robust methods of directly manipulating quantum states. Efforts
are being made to develop quantum cryptography, which will allow guaranteed secure transmission of
__________________. A more distant goal is the development of ____________________
________________, which are expected to perform certain computational tasks exponentially faster
than classical computers. Another active research topic is quantum _________________, which
deals with techniques to transmit quantum states over arbitrary distances.
© Mag. Susanne Neumann – BRG XIV (susanne.neumann@brg14.at)