e.mail: iitd.arvind@gmail.com kumara@nitj.ac.in B. Tech Physics PHX(101) By Dr. Arvind Kumar Physics Department NIT Jalandhar e.mail: iitd.arvind@gmail.com kumara@nitj.ac.in Website: https://sites.google.com/site/karvindk2013/ http://www.nitj.ac.in/physics/

Contents of Course: (For Applied Physics-I) I. Quantum Theory II. Electromagnetism Theory of Relativity IV . Crystal Structures V. Mechanical Properties VI. Thermal & Statistical Physics Total Marks = 100 First Minor = 20 Marks 2nd Minor = 20 Marks Major = 50 Marks Internal Assessment = 10 Marks

Section I Quantum Mechanics Lecture 1.1 Books:(1) A. Beiser, “Concepts of Modem Physics”, McGraw Hill (2) K S Krane, “Modern Physics”, John Wiely & Sons, Inc., 3rd Ed. (2011). (3) H K Malik & A K Malik, “Engineering Physics”, McGraw Hill Education, 2nd Ed. (2017).

Origin of Quantum Physics Upto the end of 19th Century Physics was essentially classical physics: Newtonian Physics, Maxwell electromagnetic theory, thermodynamics. Challenge to classical physics in beginning of 20th century Relativistic domain: Galilean theory fails; Einstein theory of relativity came into picture in 1905. Microscopic domain: phenomenon observed at atomic-subatomic dimensions observed due to advancement in experimental technology

Classically Wave & Particle two different entities Classically light is a wave. Interference, diffraction, polarization explained by wave nature of light But Blackbody radiations, Photoelectric effect , Compton effect need quantization of light

Max Planck idea (in 1900): Quantization of energy exchange between radiations and matter take place in discrete amount (in integer multiple of hν). This idea explained blackbody radiation spectra. Planck’s law

threshold frequency is made to fall on it. Experimental observations: Photoelectric effect Instantaneous emission of bound electrons from the surface of metal when light of frequency greater than threshold frequency is made to fall on it. Experimental observations: No matter what is the intensity of incident radiations, the electric current will be observed only when the incident radiations have frequency greater than some threshold frequency. This threshold frequency vary from metal to metal.

Once the frequency of incident radiations is greater than threshold frequency, the current will be observed instantaneously whether intensity is low or high. If the positive potential at anode is increased then more electrons will be attracted and current will increase upto a saturation value. If the intensity of light is increased, then the value of current is also observed to increase.

When the anode is put at negative potential, then electrons will be repelled by it and only those electrons will contribute to current which have sufficient kinetic energy to overcome the potential energy eV. The negative potential at which no current is observed is known stopping potential Vs

If light beams of different frequencies are used, then as shown in fig, the value of stopping potential will be large for the higher frequency.

Explanation: Classical Physics View Photoelectric effect should depend upon intensity of radiations instead of frequency of radiations. Photoelectric effect should not be an instantaneous process. Above classical explanation does not agree with the Experimental results and hence, rejected.

Quantum Physics View Einstein postulated that the light is made up of discrete packet of energy. These packets of energy are known as photons. Only those photons will be able to eject the electron which possess the energy greater than The work function of metal.

The work function of a metal surface is the minimum energy which the incident photon should possess to overcome the electron’s binding energy in the metal. The work function is the characteristic of metal and vary from one metal to other. Kinetic energy of ejected electrons will be

Using We can write or

List of Few Metals with Work Function Exercise: Photoelectric effect is possible only with bound electrons. Photons cannot Impart whole of its energy to free electron. Hint: Use total momentum and energy conservation law