1 Problem One [2 points] (Why Quantum Mechanics ?) An undergraduate physics stud

Question

1 Problem One [2 points] (Why Quantum Mechanics ?) An undergraduate physics student at UAEU, had taken the following courses during the last three semesters: classical mechanics, optics & waves, hermodynamics, during the last two semesters, which he/she got A grade in allof them. He/she thinks that these courses covered so many topics that they are enough t describe everything in our world. Give at least one argument, where you clearly explain to him/her why classical physics is inadequate to describe the microscop world, and he/she definitely needs to take quantum mechanics electromagnetism, and

Explanation / Answer

There are many phenomenon which are not described by classical mechanics. Whenever we have to study things on microscopic level we need quantum mechanics. I want to give you a simple example of photo electric effect. Photo electic is a phenomenon in which when light shines on the surface of a metallic substance, electrons in the metal absorb the energy of the light and they can escape from the metal's surface.

In classical Mechanics we consider light as a wave and in wave energy is distriuted uniformaly in entire wave So when a wave fall on metalic substance electrons in the metals absorbe all its energy untill they didn't get sufficient energy to escape from metalic surface. Hence if light of low intensity fall on metalic substance electron will emit from metal but with a time delay which is experimentally wrong.

According to experiments if light with low intesity fall on metal surface electron will not emit from surface irrespective of time and also if electron emit from surface then there is no time delay between ejection of electron.

This phenomenon was explained by Einstien he consider light as a bundel of energy which is called quanta or photon. When a photon of sufficent energy fall on metal surface electron will absorbe all its energy and ejected out from metal surface and also there is no time delay between absorbing the energy and ejection of electron. Thus photo electric effect was explained by quantum mechanics there also many phenomenon which was not explained by classical mechanics like black body radiation, compton effect etc. When ever we have to study behaviour of system at microscopic level we need quantum mechanics

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