Grade 12; PRACTICE. 4. the following chapters come under modern physics: Atoms; Nuclei; Semiconductors and devices; Communication systems 3.2 de-Broglie wavelength of a gas molecule : let us consider a gas molecule at absolute temperature T. Kinetic energy of gas molecule is given by, The document Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes is a part of, modern physics chapters, askiitians physics, chapters under modern physics, modern physics iit jee, physics mechanics notes, heat physics notes, modern physics formulas. From the data given below, determine the work function of the metal of the cathode in eV and the value of the universal constant hc/e. 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. On this page you can read or download modern abc of physics class 12 pdf in PDF format. During the phenomenon of photoelectric effect one incident photon on metal surface can eject at most only one electron. A lot of the concepts in class 12 physics are really significant as many other higher level concepts are based on … Here equation . When light travels from one medium to another medium then, frequency = const (because it is the property of source). Remaining electrons which have relatively low kinetic energy will either be attracted to cathode just after ejection or will return during their journey from cathode to anode. Download modern abc of physics class 12 pdf document. Now as all the ejected electrons from cathode start reading anode. The reason for this is equation-(2) and (3). 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. In this course, Amit Gupta will cover Wave Optics & Modern Physics for Class 12. 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
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. Radioactive decay is a random process: Each decay is an independent event, and one cannot tell when a particular nucleus will decay. The NCERT Physics Books are based on the latest exam pattern and CBSE syllabus. Current in both the cases in cut off at same reverse potential V0. 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. This will help a student save time. 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. In first case the energy of incident photon in eV is, The maximum kinetic energy of ejected electrons is, Thus work function of metal surface is given as, In second case the maximum kinetic energy of ejected electrons will become, Thus the incident energy of photons can be given as, Thus the wavelength of incident photons in second case will be. However observations shows that there exists for each surface a characterstic cutoff frequency nth, for frequency less than nth, the photoelectric effect does not occur, no matter how intense is light beam. 2nd Year Physics Notes include all 10 Chapters Short Questions, Long Questions, Past Paper Questions, Numericals, and Examples.. There are only about 105 different kinds of atoms, and they combine with each other in […] When light is incident on a metal surface it was observed that electrons are ejected from a metal surface some times even when incredicely dim light such as that from starts and distance galaxies incident on it and some time electrons not comes out from the metal surface even high energetic or high intensity light falling on the metal surface. (6) can be written 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 . 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. no. comparing it with y = mx + c, the graph between Kmax and f is a straight line with positive slope and negative intercept. 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. The variation of stopping potential with frequency v can be shown in figure shown. Revision Notes for CBSE Class 12 Physics – Free PDF Download Free PDF download of CBSE Class 12 Physics revision notes and short key-notes to score more marks in your exams, prepared by our expert Physics teachers from the latest edition of CBSE (NCERT) books. By Einstein's energy mass relation, E = mc2 the equivalent mass m of the photon is given by. All the photons of a particular frequency or wavelength posses the same energy irrespective of the intensity of the radiation. Class 12 Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes Summary and Exercise are very important for
Sol. Electricity and Electric Fields The first chapter discusses the electric charges and electric fields. This minimum frequency or threshold frequency vth can be given as. The concepts taught in the 12th standard are the fundamentals of the subject. (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. 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. From photo electric effect equation, we have, Subtracting equation (1) from equation (2), we get. Energy of photon incident on metal will not necessarily cause emission of an electron even if its energy is more than work function. Rotate this radius about OZ to get a circle on the sphere. 5. 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. 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. (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. Now, quantum theory solves these problems in providing the correct interpretation of the photoelectric effect. The work function depends on the nature of the metal. Debroglie relates particle property (momentum) with wave property (wavelength) i.e. Change q to q +dq and rotate the radius about OZ to get another circle on the sphere. If further potential difference is increased, it will not make any difference in the number of electrons reaching the anode hence, further increases in potential difference will not increases the current. When light of intensity I falls on a surface, it exerts force on that surface. 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 . Modern Physics formulae for NEET Modern physics is a branch of physics which deals with the post-Newtonian concepts in the world of physics. Newton was the first scientist who said that light is made up of tiny elastic particles called "Corpuscles" which travels with the velocity of light. Learners at any … i.e., if graph is plotted for two different metals 1 and 2, slope of both the lines is same. EduRev is like a wikipedia
of electrons emitted to the no. This is the voltage at which the faster electron from cathode will be retarded and stopped just before reaching the anode. of photons incident on metal surface is less than unity. Thus in above two graphs as frequency of incident light is same, the value of V0 is also same. So according to Newtons, light is a particle. If the potential difference applied across the discharge tube is gradually increased from the variable source, positive potential of anode starts pulling electrons from the space charge. Sol. 4 Acoustic phenomena. (iv), we get a simple formula for calculating de-Broglie wavelength of an electron. This voltage V0, we can calculate from equation (1) by substituting vf = 0 hence. 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. a particle) which he proved through balck body radiation spectrum. Find. 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. perfect preparation. (iii) The maximum velocity of the electrons ejected from the metal by light with a wavelength 1800 Å. Sol. It supports dual nature of light (wave nature and particle nature). 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. The light is reflected by the sphere along PR. Class 12 Physics Index Page is provided here. From the graph we can note the following points. 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. But at a higher voltage VP1 space charge vanishes and at this voltage anode is able to pull the slowest electron (zero kinetic energy) ejected by the cathode. (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. Consider a radius about OZ to get a making an angle q with OZ. In the classical theory, the light energy is uniformly distributed over the wavefront. To score well in the board exams, you must have a thorough understanding of each chapter of the subject. But as in the two cases the kinetic energy of fastest electron are different as frequencies are different, the stopping potential for the two cases will be different. 3 Waves in pipes and strings. Here, we have provided a complete list of chapters and subtopics discussed in the Class 12 National Council of Educational Research and Training textbook (NCERT). Chapter-11- Dual Nature of Radiation and matter. According to him the light consists of particles associated with definite amount of energy and momemtum. As the threshold frequency is defined, we can also define threshold wavelength for a metal surface. 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. CBSE Class 12 Physics Revision Notes Chapter 11 Modern Physics PDF One of the most essential aspects when studying in Class 12, is to make Physics Revision Notes. 1.7 Threshold frequency and Threshold wavelength, We have discussed that to start photoelectric emission the energy of incident photon on metal surface must be more than the work function of the metal. (i) Given that the threshold wavelength of a metal is . 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 … A high potential is applied to a discharge tube through a variable voltage source and a voltmeter and an ammeter are connected a measure the potential difference across the electrodes and to measure photoelectric current. Physics Notes for Class 12 Download. 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. Momentum is related to the kinetic energy by the equation. If the potential difference is increased with reverse polarity, the number of electrons reaching anode will decrease hence photo electric current in circuit also decreases, this we can see from figure shown which shows variation of current with increase in voltage across discharge tube in opposite direction. Further, Ex.2 The photoelectric threshold of the photo electric effect of a certain metal is 2750 Å. your solution of Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes search giving you solved answers for the same. Sol. (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. (i) The work function of emission of an electron from this metal. It is based on the two major breakthroughs of the twentieth century: Relativity and Quantum Mechanics. To pull all the electrons emitted from cathode more potential difference is required. (iii), can be written as, 3.1 de-Broglie wavelength for an electron. As , photocell will not work if irradiated by this red light no matter however intense the light will be. Ex.7 Electrons with maximum kinetic energy 3eV are ejected from a metal surface by ultraviolet radiation of wavelength 1500 Å. 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. 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. Download CBSE Class 12 Physics Modern Physics Exam Notes pdf, Physics revision notes, mind maps, formulas, examination notes, sure shot questions, CBSE Class 12 Physics Modern Physics Exam Notes. he favours dual nature of light. The NCERT Class 12th Physics textbooks are well known for it’s updated and thoroughly revised syllabus. Important Questions for Class 12 Physics Chapter Wise With Solutions. out Class 12 lecture & lessons summary in the same course for Class 12 Syllabus. Most of the concepts in class 12 physics are important as several higher level concepts are derived from the concepts that are introduced in … Let's also learn more about light with ray optics and wave optics. 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. ΔPa, force on plate due to reflected photons Fr = nr ΔPr. Dronstudy provides free comprehensive chapterwise class 12 physics notes with proper images & diagram. 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. Here p is the momentum of photon. (b) Light is incident on the cathode of a photocell and the stopping voltages are measured from light of two difference wavelengths. The study of Modern Physics is the study of the enormous revolution in our view of the physical universe that began just prior to 1900. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 volt. These notes are in PDF format that helps you to view the all chapters in one file. 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. 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. Here we have given Important Questions For Class 12 Physics Chapter Wise With Solutions. All matter is made up of tiny particles known as atoms. During this interval the electron should be absorbing energy from the beam until it had accumulated enough to escape. Physics Notes for Class 12: Physics is hands-down one of the most important subjects for students who want to have a career in engineering and other related fields. Access free study material by clicking on the respective subtopics. 1.9. Physics Class 12 PPT; Physics Class 12 PPT. Thus we can say that all the electrons reaching anode will have their speeds distributed from v1 to v2. If a light beam of frequency n (each photon energy = hn) is incident on a metal surface having work function f then for , we have. If you want Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes
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. 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. 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. 2 Mechanical Wave. 1. 1.11 Cut off Potential or Stopping Potential : We have seen with reverse polarity electrons are retarded in the discharge tube. Physics class 12 is one of the most crucial subjects for science students. Assume absorption and reflection coefficient of surface be 'a' and 'r' and assuming no transmission. The modern era is the result of the progress in Physics, and its laws are interpreted every day … What retarding potential is necessary to stop the emission of the electrons ? This graph is plotted for two incident light beams of different frequency v1 and v2and having same photon flux. (ii) Maximum kinetic energy of these electrons. 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. Ex.13 Calculate force exerted by light beam if light is incident on surface at an angle q as shown in figure. This current is1 is called saturation current. Light with frequency more than threshold frequency of cathode metal is incident on it, due to which photoelectrons are emitted from the cathode. 5 Speed of light. 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. (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. Students must learn these concepts in-depth to develop their skills in the subject and build a strong foundation. Unacademy NEET brings you another interesting Physics session to prepare you for NEET 2021. The electron emission from a metal is only depends on the work function or energy of one photons. Chapter Wise Important Questions for Class 12 Physics with Answers and Solutions Pdf free download was designed by expert teachers from latest edition of NCERT books to get good marks in board exams. 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