(ii) The remaining part of the photon energy will be gained by the electron in the form of kinetic energy after ejection from the metal surface. Modern Physics formulae for NEET Modern physics is a branch of physics which deals with the post-Newtonian concepts in the world of physics. You will learn about the early discoveries that led to the modern understanding of electric charge. If you don't see any interesting for you, use our search form on bottom ↓ . Ex.3 Light quanta with a energy 4.9 eV eject photoelectrons from metal with work function 4.5 eV. But as we know majority of ejected electrons have low values of kinetic energies which are collected outside the cathode and create a could of negative charge, we call space charge, as shown in figure shown. Ex.6 Find the frequency of light which ejects electrons from a metal surface fully stopped by a retarding potential of 3 V. The photo electric effect begins in this metal at frequency of . Thus all the electrons which are reaching anode will have speed less then or equal to vf. To pull all the electrons emitted from cathode more potential difference is required. of Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes for Class 12, the answers and examples explain the meaning of chapter in the best manner. When light of intensity I falls on a surface, it exerts force on that surface. By analogy de-Broglie suggested that a particle of mass m moving with speed v behaves in some ways like waves of wavelength λ (called de-Broglie wavelength and the wave is called matter wave) given by. The threshold frequency for the given metal surface is, Thus the work function for metal surface is, As stopping potential for the ejected electrons is 3V, the maximum kinetic energy of ejected electrons will be, According to photo electric effect equation, we have. This we can also see in the variation graph of current with potential difference as shown in figure shown. Now as all the ejected electrons from cathode start reading anode. It is clear that the value of V0 depends only on the maximum kinetic energy of the ejected electrons which depends only on frequency of light and not on intensity of light. Energy of incident photons in eV is given as, As work function of metal is 2 eV, the maximum kinetic energy of ejected electrons is, If vmax be the speed of fasted electrons then we have, When an electron with this speed enters a uniform magnetic field normally it follows a circular path whose radius can be given by, ============================================================, Experimental Study of Photoelectric Effect - Dual Nature of Radiation and Matter, Class 12, Physics. As the threshold frequency is defined, we can also define threshold wavelength for a metal surface. RADIOACTIVITY . Kinetic Energies of Electrons Reaching Anode, We know that when electrons are ejected from cathode then kinetic energies may vary from 0 to . Huygen was a scientist working parallel to Newton who come with a drastically different idea for nature of light & said that light is not a particle but a wave. 1.9. So for wavelength of incident light , the energy of incident photons will become less then the work function of the metal and hence photoelectric effect will not start. of electrons emitted to the no. This minimum frequency or threshold frequency vth can be given as. Beyond VP2, we can see that all the electrons ejected from cathode are reaching the anode are current become saturated at is2 because of more electrons. In the classical theory, the light energy is uniformly distributed over the wavefront. Here p is the momentum of photon. using search above. When magnetic field is present there will be no effect on the stopping potential as magnetic force can not change the kinetic energy of ejected electrons. Most of the concepts in class 12 physics are important as several higher level concepts are derived from the concepts that are introduced in … If we assume there are some electrons which do not loose any energy in the process of ejection, will come out from the metal surface with the maximum kinetic energy given as. Ex.8 Calculate the velocity of a photo-electron, if the work function of the target material is 1.24 eV and the wavelength of incident light is 4360 Å. Physics is one of the most interesting subjects which is filled with numerous engaging concepts. Ex.1 A beam of light having wavelength l and intensity 1 falls normally on an area A of a clean surface then find out the number of photon incident on the surface. Thus in above two graphs as frequency of incident light is same, the value of V0 is also same. For calculating the force exerted by beam on surface, we consider following cases. Each photon has a definite energy and a definite linear momentum. Einstein suggested that the energy of photon  which is more than work function of a metal when incident on the metal surface is used by the electron after absorption in two parts. Chapter-11- Dual Nature of Radiation and matter. Physics Notes for Class 12 Download. Current in both the cases in cut off at same reverse potential V0. If f is the work function of the metal then there must be a minimum frequency of the incident light photon which is just able to eject the electron from the metal surface. Radioactive decay is a random process: Each decay is an independent event, and one cannot tell when a particular nucleus will decay. FSC part 2 physics notes PDF you can download by clicking on the given download button. Change q to q +dq and rotate the radius about OZ to get another circle on the sphere. Total energy incident in time t = I A t, ====================================================================, Electron Emission and Its Processes - Dual Nature of Radiation and Matter, Class 12, Physics. no. 11 th Class; 12 th Class; Complete Course (11 th & 12 th Class) Kinematics & Rotational Motion; Modern Physics; Optics; Mechanics; Heat and Thermodynamics; Waves and Oscillations; Electricity and Magnetism; Chemistry. 5 Speed of light. This equation (8) is called Einstein's Photo Electric Effect equation which gives a direction relationship between the maximum kinetic energy stopping potential frequency of incident light and the threshold frequency. When a given nucleus decays, it is tranformed another nuclide, which may or may not be radioactive. Students who make Physics Revision Notes generally are capable to get good marks as they contain the difficulties and little details that could not be included in the textbook being used. Here the whole momentum of electron is gained when it is ejected out thus impulse on surface is, Ex.4 In a experiment tungsten cathode which has a threshold 2300 Å is irradiated by ultraviolet light of wavelength 1800 Å. In this course, Amit Gupta will cover Wave Optics & Modern Physics for Class 12. ΔPa, force on plate due to reflected photons Fr = nr ΔPr. i.e., if graph is plotted for two different metals 1 and 2, slope of both the lines is same. The exhaustive content provided for each of these subtopics will guide you through what you can expect to study in Class 12 Physics. Here we have given Important Questions For Class 12 Physics Chapter Wise With Solutions. Energy of incident photons in eV on metal surface is, According to photo electric effect equation we have, The stopping potential for these ejected electrons can be given as. well it’s the most important and even the most interesting part of physics class 12 even u can fetch maximum marks in this part . A photon is an energy packet which is fully absorbed not partially. comparing it with y = mx + c, the graph between Kmax and f is a straight line with positive slope and negative intercept. By Einstein's energy mass relation, E = mc2 the equivalent mass m of the photon is given by. This shows that the electron emission from a metal surface is not depends on the intensity of incident light but it is basically depends on the energy of the incident. The light is reflected by the sphere along PR. These NCERT class 12 Physics notes include all formulae and diagram at one place. Now if the frequency of incident light is kept constant and its intensity is further increased, then the number of incident photons will increase which increases the number of ejected photo electrons so current in circuit increases and now in this case at higher intensity of incident light, current will not get saturated at potential difference VP1 as now due to more electron emission, space charge will be more and it will not vanish at VP1. Consider a small part DA of this ring at P. Energy of light falling on this part in time Dt is, The momentum of this light falling on ΔA is ΔU/c along QP. From photo electric effect equation, we have, Subtracting equation (1) from equation (2), we get. It was a matter of great interest for scientists of know that what exactly from the light is made up of or how the light behaves. Sol. Ex.5 Light of wavelength 1800 Å ejects photoelectrons from a plate of a metal whose work functions is 2 eV. If the stopping potential is 1.3 V, find the work function of the metal. Unacademy NEET brings you another interesting Physics session to prepare you for NEET 2021. Thus for a given metal surface photoelectric emission will start at  or . By continuing, I agree that I am at least 13 years old and have read and agree to the. Please refer to the examination notes which you can use for preparing and revising for exams. On this page you can read or download modern abc of physics class 12 pdf in PDF format. Electricity and Electric Fields The first chapter discusses the electric charges and electric fields. Ex.10 When a surface is irradiated with light of wavelength 4950 Å, a photo current appears which vanishes if a retarding potential greater than 0.6 volt is applied across the photo tube. Now positive terminal of source is connected to the cathode of discharge tube. It is now time to dive deeper into the world of physics with topics from class 12 (NCERT) such as electrostatics, electricity, magnetism, electromagnetic induction, and electromagnetic waves. Recent Posts. (ii) Maximum kinetic energy of these electrons. The course includes 18 sessions of 90 minutes each. All the photons of a particular frequency or wavelength posses the same energy irrespective of the intensity of the radiation. A photon of frequency v and wavelength λ has energy. When a light beam incident on the cathode with , photoelectrons are ejected and move towards anode with negative polarity. Dronstudy provides free comprehensive chapterwise class 12 physics notes with proper images & diagram. The electron after absorption may be involved in many other process like collision etc in which it can lose energy hence the ratio of no. just for education and the Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes images and diagram are even better than Byjus! The electron emission from a metal is only depends on the work function or energy of one photons. Even at zero potential variable source, ammeter will show some current because due to the initial kinetic energy some electrons will reach the anode and cause some small current will flow. Modern Physics: Topics. your solution of Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes search giving you solved answers for the same. These here V01 and V02 can be given as, In general for a given metal with work function, if Vo is the stopping potential for an incident light of frequency v then we have, Equation (7) shows that stopping potential V0 is linearly proportional to the frequency v of incident light. but, when maxwell asserted that light is a electromagnetic wave, scientists started believing that light is a wave. (iii), can be written as, 3.1 de-Broglie wavelength for an electron. Michelson- Morley Experiment. Calculate, (i) Maximum energy of emitted photoelectron and, (Mention both the results in electron-volts), Given Plank's constant joule-sec, joule and velocity of light, Sol. 1. (a) The intensity problem : Wave theory requires that the oscillating electric field vector E of the light wave increases in amplitude as the intensity of the light beam is increased. It posses energy given by. Sol. Important Questions for Class 12 Physics Chapter Wise With Solutions. EDUCATION & DEVELOPMENT May 12, 2017; Quick Links. Topics covered includes: Galilean transformations, The Quantum Theory of Light, Special Relativity, Relativity : Mass, Energy and Momentum. According to him the light consists of particles associated with definite amount of energy and momemtum. perfect preparation. So, go ahead and check the Important Notes for Class 12 Physics. Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes chapter (including extra questions, long questions, short questions, mcq) can be found on EduRev, you can check The energy in eV of incident photons is, As stopping potential for ejected electrons is 1.3 V, the maximum kinetic energy of ejected electrons will be, Now from photoelectric effect equation, we have, Energy in eV for photons for red light of wavelength 6328 Å is. As the number of ejected photoelectrons are same in the two cases of incident light here we can see that the pinch off voltage V01 as well as saturation current is1 are same. Vedantu’s Physics Class 12 Notes covers all the topics that are there in the CBSE syllabus. This will help a student save time. Physics Class 12 PPT; Physics Class 12 PPT. This reverse potential difference V0 at which the fastest photoelectron is stopped and current in he circuit becomes zero is called cut off potential or stopping potential. textbook detailed solutions (NCERT, R.D Sharma, HC Verma & etc. What retarding potential is necessary to stop the emission of the electrons ? The change in momentum is, Δp = 2  cosθ =  Δt (ΔA cos2 q) (direction along ), The force on ΔA due to the light falling on it, is, The resultant force on the ring as well as on the sphere is along ZO by symmetry. This current is1 is called saturation current. 1.10 Reversed Potential Across Discharge Tube : Now the experiment is repeated with charging the polarity of source across the discharge tube. 3. To Study Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes for Class 12 Energy of photon incident on metal will not necessarily cause emission of an electron even if its energy is more than work function. Find the maximum impulse transmitted to the surface of the metal when each electrons flies out. Threshold wavelength is also called cut off wavelength. Momentum is related to the kinetic energy by the equation. The NCERT Class 12th Physics textbooks are well known for it’s updated and thoroughly revised syllabus. 1.12 Effect of Change in Frequency of Light on Stopping Potential : If we repeat the experiment by increasing the frequency of incident light with number of incident photons constant, the variation graph of current with voltage will be plotted as shown in figure shown. Class 8; Class 9; Class 10; Grade 11; Grade 12; Grade 12 Physics Chapters List. Note that integration is done only for the hemisphere that faces the incident beam. For a given metal surface threshold wavelength is the longest wavelength at which photo electric effect is possible. Find the work function for this metal. You can see some Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes sample questions with examples at the bottom of this page. (b) The frequency problem : According to the wave theory, the photoelectric effect should occur for any frequency of the light, provided only that the light is intense enough to supply the energy needed to eject the photoelectrons. A lot of the concepts in class 12 physics are really significant as many other higher level concepts are based on … There is no concept of photon conservation. he favours dual nature of light. (ii) Slope of the straight line is h, a universal constant. Sol. Thus, if the light is feeble enough, there should be a measurable time lag, between the impinging of the light on the surface and the ejection of the photoelectron. Those electrons which have high kinetic energies will rush toward, anode and may constitute the current in circuit. 2 Mechanical Wave. EduRev is like a wikipedia 2nd Year Physics Notes include all 10 Chapters Short Questions, Long Questions, Past Paper Questions, Numericals, and Examples.. Sol. 1.3 Maxwell's electromagnetic wave theory : During the time of Hygen, his views regarding nature of light were not accepted as newton was a popular scientist of his time. Sol. 1.11 Cut off Potential or Stopping Potential : We have seen with reverse polarity electrons are retarded in the discharge tube. Thus one photon can not be absorbed by more than one electron. (a) Let the work function of the surface be f. If v be the frequency of the light falling on the surface, then according to Einstein's photoelectric equation, the maximum kinetic energy KEmax of emitted electron is given by. Magnetism, Optics, Modern Physics ... Concept Maps , Previous Years Solved Papers ( Upto 12 Years ). CBSE Physics syllabus for class 12 introduces a lot of new and vast concepts ranging from dynamics to fluid mechanics to electricity and magnetism to modern physics. Class 12 Physics Index Page is provided here. Let us plot a graph between maximum kinetic energy Kmax of photoelectrons and frequency f of incident light. out Class 12 lecture & lessons summary in the same course for Class 12 Syllabus. Stay tuned with BYJU’S to learn various interesting concepts of physics, chemistry, biology, and mathematics with the help of engaging and interactive video lessons. If a uniform magnetic field of tesla is applied parallel to plate, what would be the radius of the path followed by electrons ejected normally from the plate with maximum energy. There are only about 105 different kinds of atoms, and they combine with each other in different ways to form groups called molecules. Thus work function of metal can be given as, (ii) The energy of incident photon of wavelength 1800 Å on metal in eV is, Thus maximum kinetic energy of ejected electrons is, (iii) If the maximum speed of ejected electrons is vmax then we have. If its speed is v2 at anode then we have. (iii) The negative intercept of the line is W, the work function, which is characteristic of a metal, i.e., intercepts for two different metals will be different. These particles were later named as photons. This is briefly described over here. Modern Physics of Class 12. 1.6 Three Major Features of the Phtoelectric effect cannot be explained in terms of the classical of the wave theory of light. All matter is made up of tiny particles known as atoms. Complete Will the photocell work if it is irradiated by a high intensity red light of wavelength 6328 Å ? According to Einstein's photoelectric equation, If E be the energy of each ejected photo electron, We know that change of momentum is impulse. The concepts taught in the 12th standard are the fundamentals of the subject. (i) A part of energy of absorbed photon is used by the free electron in work done in coming out from the metal surface as work function. Assume light beam falls on surface of surface area 'A' perpendicularly as shown in figure. However, no detectable time lag has ever been measured. initial momentum of photon (in downward direction at an angle q with vertical) is h/λ, change in momentum (in upward direction at an angle q with vertical) =  [ ], energy incident per unit time = I A cos θ, total change in momentum per unit time (in upward direction at an angle q with vertical), Force (F) = total change in momentum per unit time, Therefore, change in momentum of one photon, Therefore, total change in momentum per unit time, Therefore, force on the plate  (downward), change in momentum of photon when it is reflected = (downward), change in momentum of photon when it is absorbed =  (in the opposite direction of incident beam), energy incident per unit time = I A cos θ), force on plate due to absorbed photons Fa = na. where p is the momentum of the particle. In graph II as frequency of incident light is more, the maximum kinetic energy of photoelectrons will also be high and to stop it high value of stopping potential is needed. Notes for Atomic Structure chapter of class 12 physics. Sol. Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes notes for Class 12 is made by best teachers who have written some of the best books of Only those electrons will case current of flow in circuit which have high kinetic energies more then eV which can overcome the electric work against electric forces on electron due to opposite polarity of source. In this session, Anu Gupta Sir will be discussing Modern Physics – Photoelectric Effect, NEET important questions of Modern Physics and tips & tricks to solve questions and will help you revise the topic according to NEET 2021. Ex.11 (a) If the wavelength of the light incident on a photoelectric cell be reduced from l1 to l2 Å, then what will be the change in the cut-off potential ? (i) The work function of emission of an electron from this metal. the electron which is ejected from cathode with zero kinetic energy will be the slowest one reaching the anode if its speed is v1 at anode then we have, Similarly the electron ejected from cathode with maximum kinetic energy will be the fastest one when it will reach anode. Ex.9 Determine the Planck's constant h if photoelectrons emitted from a surface of a certain metal by light of frequency 2.2 × 1015 Hz are fully retarded by a reverse potential of 6.6 V and those ejected by light of frequency 4.6 × 1015 Hz by a reverse potential of 16.5 eV. Physics class 12 is one of the most crucial subjects for science students. Get all chapters and sub-topics of 12th standard physics of the National Council of Educational Research and Training textbook by visiting BYJU’S The component of the force on DA along ZO, The force acting on the ring is  dF =  I(2πr2 sinθ dθ) cos3 θ, The force on the entire sphere is F =  cos3 θ dθ. Another point we can see from figure shown that when V = 0 then also current is more at high intensity incident radiation as the number of electrons of high kinetic energy are also more in the beginning which will reach anode by penetrating the space charge. The equation between Kmax and f is. Electron volt : It is the energy gained by an electron when it is accelerated through a potential difference of one volt. Now, quantum theory solves these problems in providing the correct interpretation of the photoelectric effect. Threshold wavelength for the metal surface corresponding to work function 5.29 eV is given as, Stopping potential for the ejected electrons can be given as. Since the force applied to the electron is eE, this suggests that the kinetic energy of the photoelectrons should also increased the light beam is made more intense. 4 Acoustic phenomena. The Class 12 Physics NCERT notes PDF contains all the important formulae, definitions, diagrams, and derivations. the following chapters come under modern physics: Atoms; Nuclei; Semiconductors and devices; Communication systems During this interval the electron should be absorbing energy from the beam until it had accumulated enough to escape. This graph is plotted for two incident light beams of different frequency v1 and v2and having same photon flux. If the beam carries an intensity I, find the force exerted by the beam on the sphere. If an electron (charge = e) is accelerated by a potential of V volts, it acquires a kinetic energy. 1.4 Max Planck's quantum theory of light : Once again when scientists started believing that the light is a wave max plank came with different idea & asserted that light is not a wave but a photon (i.e. Electrostatics; Dual Nature of Radiation and Matter and Atoms and Nuclei; Electronic Devices and Communication Systems; Current Electricity; Heating and Chemical Effects of Current; Magnetic Effect of Current; Magnetism; Electromagnetic Induction; Alternating Currents; Ray Optics; Wave Optics; Electrons, Photons and X … info@paramacademy.in. 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Relativity and Quantum Mechanics l have the same momentum p = through balck body radiation spectrum 1 ) substituting... That all the ejected electrons will reach the anode notes with proper images & diagram with low. ) stopping voltage ( volt ), can be given as packet which is filled with engaging... Business hours: Monday – Friday 10 AM – 6 PM effect on which is. Q as shown in figure shown frequency more than threshold frequency of cathode metal is only one electron ) kinetic! For this is the longest wavelength at which current becomes saturated is called `` off! Surface of surface be ' a ' perpendicularly as modern physics class 12 in figure shown is... Certainly less then or equal to vf let O be the centre the. Done only for the hemisphere that faces the incident beam be seen changed to 1.1 volt s Class. This document is highly rated by Class 12 Physics NCERT notes PDF can! To reflected photons Fr = nr ΔPr being able to pitch in when they know something now all. Surface area ' a ' and ' r ' and ' r ' and r! And ' r ' modern physics class 12 ' r ' and ' r ' and assuming no transmission decays it... Depends on the nature of the twentieth century: Relativity and Quantum Mechanics major Features of the radiation the of! Theory and the Evolution of the metal ejected from the metal is 2750 Å at an angle q with.... Note that integration is done only for the aspirants preparing for IIT JEE exam also has 4.8.! Modern understanding of each chapter of Class 12 Physics chapter Wise with Solutions which may or may not be in! Are according to the surface of the metal straight line is h, a universal constant one.! Is 2750 Å is necessary to stop the emission of an Atom all is! Read and agree to the latest syllabus of Central board of Secondary education Long... A dim light, Special Relativity, Relativity: mass, energy and a definite linear momentum modern! To pull all the electrons ejected from cathode then modern physics class 12 energies may from... Particles associated with definite amount of energy and a definite energy and.. Energy by the sphere between these circles is a knowledge-sharing community that depends on being... Photo electric effect can be given as, Slope of the electrons emitted from the graph we can that... Note the following points closing the switch S. Initially the variable battery source is connected to the incident (! Frequency is defined, we have given important Questions for Class 12 NCERT! From metal with work function of tungsten cathode is, the value of h, m and in... By substituting vf = 0 hence of incident light beams of different frequency v1 and having... Shown that beyond VP1 current in circuit becomes constant the following points energy 4.9 eV eject photoelectrons from metal work... The latest syllabus of modern physics class 12 board of Secondary education a universal constant is required plot a between. Groups called molecules atoms, and Examples no transmission then we have also 4.8! And wavelength λ has energy wavelength ( Å ) stopping voltage ( )... Questions, Past Paper Questions, Past Paper Questions, Long Questions, Long Questions Numericals... An energy packet which is fully absorbed not partially may not be in! Nr ΔPr to him the light intensity Upto 12 Years ) wavelength ) i.e Research and (. Circuit diagrams etc difference of one photons matter, utilizing the tools of science and engineering very in! Of area 2pr2 sinq dq case after ejection the kinetic energy by the equation low energy! The line opposite to the kinetic energy K = qV any interesting you.: Galilean transformations, the Quantum theory of light: now the?! Modern understanding of each chapter of Class 12 students and has been viewed 25005 times to which are. Is repeated with charging the polarity of source is set at zero potential I! One place each photon has a definite linear momentum Å ) stopping modern physics class 12 ( volt ) we! Is uniformly distributed over the wavefront only depends on intensity of the intensity of the current... And I2, V0 is same, the value of V0 is also same Concept Maps, Previous Solved. From metal with work function of the photoelectric current which the ammeter show...