Quantum theory by Robert MacKay

Some have speculated about the similarities between quantum theory and Eastern Philosophy For example see: “The Tao of Physics” by Fritjof capra or “The Dancing Wu Li Masters” by Gary Zukav

JJ Thompson discovers electron (1897) The discovery of these negatively-charged particles led to the formulation of a Model in which negative charges were scattered in a positively-charged medium. This model became known as the "plum pudding", borrowing the name from a popular English dessert of the time. http://www.aip.org/history/electron/

Amidst glowing glass tubes and the hum of electricity, the British physicist J.J. Thomson was venturing into the interior of the atom. At the Cavendish Laboratory at Cambridge University, Thomson was experimenting with currents of electricity inside empty glass tubes. He was investigating a long-standing puzzle known as "cathode rays.“ He soon discovered that these were tiny particles “corpuscles” of charge. These were later referred to as electrons.

1900 Max Planck successfully uses the idea of energy quanta to explain the radiation spectrum coming from a very hot object. Planck introduced the idea that the energy of the vibrating atoms emitting the radiation can only exist as integral multiples of hf. (i.e. E=n hf) Here n is 1, 2, 3, 4, …. f is the frequency in Hz E is the energy (Joules) And h is a very tiny number 6.63x10-34 J-s

E=n(hf) means that the energy of an oscillating can only have discrete values. Or the oscillator energy is quantized. Planck’s successful use of the idea that nature (in the case energy) was quantized was the first time that the quantization idea was used to successfully explain experimental results. Planck never really accepted the theory of nature “quantum Physics” that ultimately grew out of his original discovery (that quantization seems to help explain experimental observations).

1905 Albert Einstein publishes 4 monumental papers 1905 Albert Einstein publishes 4 monumental papers. 2 on relativity, one on Brownian motion, and one on the photoelectric effect. The Nobel Prize in Physics 1921 was awarded to Albert Einstein "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect".

The photoelectric effect Einstein suggested that the energy in a beam of light is quantized (or comes in the form of packets) The quantum of light energy is a photon. The photon energy E=hf E is the energy (Joules) f is the frequency in Hz h is Planck’s constant

Photo Electric Effect.

wavelength High Energy photons Low Energy photons

Low frequency (energy) photons will not kick electrons from the plate no matter how bright the light is. High frequency (energy) photons kick electrons from the plate even at low light intensity

Question The work function for a particular metal f is 4.0 electron Volts (eV) * If photons with energy of 5.0 eV strike the metal surface what is the maximum kinetic energy of the ejected electrons? * 1 eV is the energy gained by 1 electron (or proton) when accelerated by 1.0 Volt

Question The work function for a particular metal f is 4.0 electron Volts (eV) * If photons with energy of 5.0 eV strike the metal surface what is the maximum kinetic energy of the ejected electrons? Given : f =4.0 eV hf= 5.0 eV Want : KE Use : hf= f +KE or KE =hf- f= 5.0 eV - 4.0 eV = 1.0 eV * 1 eV is the energy gained by 1 electron (or proton) when accelerated by 1.0 Volt

Question The work function for a particular metal f is 4.0 electron Volts (eV) * If photons with energy of 5.0 eV strike the metal surface what is the maximum kinetic energy of the ejected electrons? Given : f =4.0 eV hf= 5.0 eV Want : KE Use : hf= f +KE or KE =hf- f= 5.0 eV - 4.0 eV = 1.0 eV If the photon energy doubled to 10 ev the kinetic energy would Double also Less than double More than double * 1 eV is the energy gained by 1 electron (or proton) when accelerated by 1.0 Volt

Question The work function for a particular metal f is 4.0 electron Volts (eV) * If photons with energy of 5.0 eV strike the metal surface what is the maximum kinetic energy of the ejected electrons? Given : f =4.0 eV hf= 5.0 eV Want : KE Use : hf= f +KE or KE =hf- f= 5.0 eV - 4.0 eV = 1.0 eV If the photon energy doubled to 10 ev the kinetic energy would Double also Less than double ****More than double*** The kinetic energy would go from 1.0 eV to 6.0 eV * 1 eV is the energy gained by 1 electron (or proton) when accelerated by 1.0 Volt

Radio active particles Radioactivity was first discovered during 1896 by the French scientist Henri Becquerel, while working on phosphorescent materials. See http://en.wikipedia.org/wiki/Radioactive_decay Alpha particles are essentially Helium nuclei often emitted from radioactive decay. Alpha particles have a +2 electric charge (2-protons) and are very massive relative to electrons (2 protons and 2 neutrons make up the mass).

1911 Ernest Rutherford suggests the use alpha particles to probe the interior of atoms http://micro.magnet.fsu.edu/electromag/java/rutherford/ A very thin piece of gold foil is bombarded with alpha particles. Rutherford was shocked to observe alpha particles bouncing backward on very rare occasions. He concludes that most of the mass of matter has a positive charge and is highly localized in the nucleus.

Rutherford suggest a solar system model for the atom. The problem with this is that as the electron orbits the nucleus its velocity continuously changes direction and hence it accelerates. Maxwell found that whenever charges accelerate they emit electromagnetic energy. Hence the electron proton system would continuously lose energy and the electron would quickly spiral into the nucleus.