About IOP ebooks. After a post-doctoral appointment at the University of Alberta in Edmonton, he joined the physics department at the University of Connecticut in His research focused on the relationship between canonical quantization techniques and the functional approach of path integrals, which led to authoring the monograph Path Integrals and Quantum Processes. This site uses cookies.

## What Is Quantum Mechanics?

By continuing to use this site you agree to our use of cookies. To find out more, see our Privacy and Cookies policy. Close this notification. A Concise Introduction to Quantum Mechanics. Download ebook Download PDF book. Download ePub book You need an eReader or compatible software to experience the benefits of the ePub3 file format.

What is the human body and the Earth, the Sun, the Universe made of? What if the history of the universe were squeezed into the period of one year? What are the coldest and the hottest objects in the universe? What is the electromagnetic spectrum? What is a planet?

## Quantum mechanics

What is a dwarf planet? Why do the planets orbit the Sun? If you quote this material please be courteous and provide a link. Citations Sources Inquiries Privacy Policy. Thus it is possible to calculate the quantum wavelength of a particle through knowledge of its momentum. This was important because wave phenomena, such as diffraction, are generally only important when waves interact with objects of a size comparable to their wavelength. Fortunately for the theory, the wavelength of everyday objects moving at everyday speeds turns out to be incredibly small.

So small in fact that no Quantum Mechanical effects should be noticeable at the macroscopic level, confirming that Newtonian Mechanics is perfectly acceptable for everyday applications as required by the Correspondence Principle. Conversely, small objects like electrons have wavelengths comparable to the microscopic atomic structures they encounter in solids. Thus a Quantum Mechanical description, which includes their wave-like aspects, is essential to their understanding.

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Hopefully the foregoing discussion provides a convincing enough argument to use Quantum Mechanical ideas when dealing with electrons in solids. Next we must address the question of how exactly one describes electrons in a wave-like manner The approach suggested by Schrodinger was to postulate a function which would vary in both time and space in a wave-like manner the so-called wavefunction and which would carry within it information about a particle or system.

The time-dependent Schrodinger equation allows us to deterministically predict the behaviour of the wavefunction over time, once we know its environment. The information concerning environment is in the form of the potential which would be experienced by the particle according to classical mechanics if you are unfamiliar with the classical concept of potential an explanation is available.

### What is myPrint?

Whenever we make a measurement on a Quantum system, the results are dictated by the wavefunction at the time at which the measurement is made. It turns out that for each possible quantity we might want to measure an observable there is a set of special wavefunctions known as eigenfunctions which will always return the same value an eigenvalue for the observable.

Even if the wavefunction happens not to be one of these eigenfunctions, it is always possible to think of it as a unique superposition of two or more of the eigenfunctions, e. If a measurement is made on such a state, then the following two things will happen: The wavefunction will suddenly change into one or other of the eigenfunctions making it up.

## quantum mechanics | Definition, Development, & Equations | etavuleqyz.cf

This is known as the collapse of the wavefunction and the probability of the wavefunction collapsing into a particular eigenfunction depends on how much that eigenfunction contributed to the original superposition. More precisely, the probability that a given eigenfunction will be chosen is proportional to the square of the coefficient of that eigenfunction in the superposition, normalised so that the overall probability of collapse is unity i. The measurement will return the eigenvalue associated with the eigenfunction into which the wavefunction has collapsed.

Clearly therefore the measurement can only ever yield an eigenvalue even though the original state was not an eigenfunction , and it will do so with a probability determined by the composition of the original superposition. There are clearly only a limited number of discrete values which the observable can take. We say that the system is quantised which means essentially the same as discretised.

Once the wavefunction has collapsed into one particular eigenfunction it will stay in that state until it is perturbed by the outside world.

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