Photo electric effect Photo electric effect When light or E.M. radiation of suitable frequency or wavelength falls on a metal surface, it emits electrons. The process of emission of electrons from a metal surface, when illuminated by light of suitable wavelength or frequency is photoelectric effect. The electrons so emitted are photoelectrons. Experimental Arrangement  T = An evacuated glass tube with a quartz window W P = Photoelectrical sensitive plate C = Hollow cylinder which have a small hole to permit the incident light G = A sensitive galvanometer or ammeter P is connected with negative end of a battery with G C is connected with positive end of a battery Working When light of suitable frequency falls on P from a source, the photoelectrons are emitted. Since collecting cathode C is connected to positive terminal of battery, so these electrons are attracted towards C. Thus photo electric current (I C ) flows from P to C, an...

Introduction of quantum mechanics Newton’s law of mechanics are based on the elementary idea of physics or classical mechanics. This mechanics is applicable only on macroscopic particles. The basic principle used in classical mechanics are Lagrange’s equations, Hamilton’s equations. Classical physics also contain electromagnetism, thermodynamics and statistical mechanics. Interference, diffraction and polarization of light can be explained by wave nature of light. Photoelectric effect, Compton effect etc. can not be explained by wave theory. These phenomenon can be explained by Quantum mechanics. Black body Radiation An object which completely absorbs the radiations falling on it, whatever be the wavelength, is known as black body. No body absorbs 100% radiations falling on it. Lamp black, carbon black, platinum black absorbs 90-95% radiations falling on them, so they can be considered as a black body. If a black body be placed in an isothermal enclosure then the bod...

Maxwell Boltzmann Statistics It is applied to distinguishable particles. Particles are distinguishable from each other. Each cell may contain 0, 1, 2, … n i particles. Total number of particles of system remain constant, n = Σn i  = constant Sum of energies of all the particles in the different groups taken together i.e., total energy of the system remain constant E = Σn i ε i = constant Consider a system of n distinguishable particles. These particles be divided into groups or levels such that Energy levels    ε 1,  ε 2,  ε 3, ... ε i  Degeneracies    g 1,  g 2,  g 3, ... g i  Occupation number    n 1,  n 2,  n 3, ... n i  Consider a box, divide it into g i  sections, distribute n i  particles among them. Number of ways to distribute n 1 particles in first state are                     ...

Planck's Radiation Law This is application of Bose-Einstein statistics. According to quantum theory, the radiant energy occurs in energy packets. These packets are known as quanta or photon. The energy of packet should be h times the frequency of photon. The momentum of each packet should be h/c times the frequency of photon. The photons are indistinguishable particles having zero rest mass and having spin quantum number 1. Thus photons are Bose particle and hence Bose Einstein statistics can be applied on it. By using Planck's radiation law, we can also establish the Rayleigh Jean’s law, Wein’s law and Stefan-Boltzmann’s law. Planck's radiation law According to Planck, the energy density of radiations emitted from a black body in the wavelength range λ and λ + dλ is, u λ  dλ = (N λ  dλ)  E  Here N λ  dλ = Number of oscillators (number of modes of vibration) in the wavelength range λ and λ + dλ E is average energy of Planck's oscilla...

Thomson’s parabola method Positive ray analysis This method is used to find the charge to mass ratio. Thomson parabola method T = Discharge tube, the pressure of gas in this tube is kept 0.01 mm of Hg E = Capillary tube C = Cathode, which is perforated with an extremely small holes W = Water jacket, used to cool the cathode A and B = Metallic plates, the electric field is applied between these plates N and S = North and south poles of a heavy magnet K = Highly evacuated camera P = Photographic plate R = Liquid air trap, used to keep the pressure in K quite low Working To ensure the supply of the gas, a steady steam of the gas is allowed to pass through E and after circulating the tube, it is escaped through M. The positive ion produced in T move towards C. The ion which reaches C axially. pass through its fine hole in the form of narrow beam. After crossing C, the parallel beam of ions enters into the electric and magnetic...

पतले लेन्स द्वारा उत्पन्न विचलन पतले लेन्स द्वारा उत्पन्न विचलन इस चित्र में बिम्ब  O  का प्रतिबिम्ब  I  है। ΔOPI  से,                      δ = ∝ + β                          ...(1) उपाक्षीय किरणों के लिए  ∝  तथा  β  का मान अत्यन्त अल्प होता है। इसलिए,  ∝ ≈ tan ∝  तथा  β ≈ tan β ΔOPL  से,                     ∝ ≈ tan ∝ = PL / OL            या      ∝ = h / (-u)                    ...(2) ΔPIL  से,                      β ≈ tan β = PL / LI           या      β = h / v   ...

Chromatic aberration and its reduction Aberration The spherical surfaces and lenses are used to create the images of given objects. If we find the position, size and forms of images by using simple equations, then there will be several defects or aberration in images. The defects in images formed by a lens or combination of lenses are known as aberration. Chromatic aberration or Colour defect When white light incident on a prism, then after refraction form the prism it splits into seven colours. In the same way if white light incident on a lens and after refraction from the lens, we get the images of different colours, then such defect of lens is known as chromatic aberration or colour defect. Because a lens can be assumed as a combination of several prisms, and their angle of refraction decreases as we go from centre to the corner. Reason The refractive index of lens material is different for different colours or the light of different wavele...

Maxwell’s Equations Maxwell's equations for vacuum These equations form the foundation of electromagnetic theory. These equations in electromagnetism have the same importance as the Newton’s law of motion in mechanics. Maxwell’s equations generate the wave equations that predict the existence of electromagnetic waves propagate with the speed of light. Gauss’s law of electrostatics (Maxwell's first equation) According to Gauss's law of electrostatics the total electric flux through a closed surface is 1/ε 0 times the total charge enclosed by the surface. If ρ is volume charge density, then the charge enclosed by the surface is                     Gauss' law From divergence theorem This is differential form of Gauss's law of electrostatics and is also known as Maxwell's first equation . Gauss’s law of magnetostatics (Maxwell's second equation)...