Quantum Physics Summary

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.

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 = ) 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.