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. Modern Physics of Class 12. NCERT Books Class 12 Physics: The National Council of Educational Research and Training (NCERT) publishes Physics textbooks for Class 12. As the threshold frequency is defined, we can also define threshold wavelength for a metal surface. Electron volt : It is the energy gained by an electron when it is accelerated through a potential difference of one volt. In this course, Amit Gupta will cover Wave Optics & Modern Physics for Class 12. Photons no matters in number of photons are very less in a dim light, photo electric effect can be seen. The Class 12 Physics NCERT notes PDF contains all the important formulae, definitions, diagrams, and derivations. Combining all these relations Eq. In the classical theory, the light energy is uniformly distributed over the wavefront. However observation shows that maximum kinetic energy is independent of the light intensity. 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. 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. i.e., if graph is plotted for two different metals 1 and 2, slope of both the lines is same. When a different source of light is used, it is found that the critical retarding potential is changed to 1.1 volt. But how many electrons comes out from the metal is depends on intensity of the falling light on energy of the light. (iii), can be written as, 3.1 de-Broglie wavelength for an electron. For a given metal surface threshold wavelength is the longest wavelength at which photo electric effect is possible. 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. Dronstudy provides free comprehensive chapterwise class 12 physics notes with proper images & diagram. Momentum is related to the kinetic energy by the equation. This document is highly rated by Class 12 students and has been viewed 25005 times. 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. (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. Sol. Thus all the ejected electrons from the metal surface may have different kinetic energies, distributed from 0 to . 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. Please refer to the examination notes which you can use for preparing and revising for exams. 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. Get all chapters and sub-topics of 12th standard physics of the National Council of Educational Research and Training textbook by visiting BYJU’S For calculating the force exerted by beam on surface, we consider following cases. Let O be the centre of the sphere and OZ be the line opposite to the incident beam (figure). 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. 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. Here p is the momentum of photon. 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. 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. 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. The variation of stopping potential with frequency v can be shown in figure shown. (ii) Maximum kinetic energy of these electrons. Ex.5 Light of wavelength 1800 Å ejects photoelectrons from a plate of a metal whose work functions is 2 eV. You can also find Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes ppt and other Class 12 slides as well. 1.9. So according to Newtons, light is a particle. Structure Of An Atom All matter is made up of tiny particles known as atoms. of electrons emitted to the no. We can see one more thing in figure shown that the graphs plotted for two different intensities I1 and I2, V0 is same. Thus all the electrons which are reaching anode will have speed less then or equal to vf. This we can also see in the variation graph of current with potential difference as shown in figure shown. The photon posses momentum and is given by, A photon is a packet of energy. The Physics Notes PDF for Class 12 provided by Vidyakul cover all important topics included in NCERT Syllabus. A shown in graph, we can see as potential difference increases, current in circuit increases. If you don't see any interesting for you, use our search form on bottom ↓ . The work function of tungsten cathode is, The maximum kinetic energy of ejected electrons can be given as. 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. Find the work function for this metal. Rotate this radius about OZ to get a circle on the sphere. Physics class 12 is one of the most crucial subjects for science students. The work function depends on the nature of the metal. 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. EduRev is a knowledge-sharing community that depends on everyone being able to pitch in when they know something. 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. This current is1 is called saturation current. So, go ahead and check the Important Notes for Class 12 Physics. (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. a particle) which he proved through balck body radiation spectrum. 6 Interference ,Diffraction and Polarisation. Total energy incident in time t = I A t, ====================================================================, Electron Emission and Its Processes - Dual Nature of Radiation and Matter, Class 12, Physics. This we can see in figure shown that beyond VP1 current in circuit becomes constant. Class 12 Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes Summary and Exercise are very important for
Here we can see that at a particular reverse voltage V0, current in circuit becomes zero. Modern physics is an effort to understand the underlying processes of the interactions with matter, utilizing the tools of science and engineering. Modern Physics: Topics. Download modern abc of physics class 12 pdf document. The exhaustive content provided for each of these subtopics will guide you through what you can expect to study in Class 12 Physics. The course includes 18 sessions of 90 minutes each. 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. If the beam carries an intensity I, find the force exerted by the beam on the sphere. Access free study material by clicking on the respective subtopics. Let's also learn more about light with ray optics and wave optics. 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. Will the photocell work if it is irradiated by a high intensity red light of wavelength 6328 Å ? Wavelength (Å) Stopping voltage (volt), 4000 1.3, 4500 0.9, Sol. The part of the sphere between these circles is a ring of area 2pr2 sinq dq. The NCERT Class 12th Physics textbooks are well known for it’s updated and thoroughly revised syllabus. 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
3. 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. Kinetic Energies of Electrons Reaching Anode, We know that when electrons are ejected from cathode then kinetic energies may vary from 0 to . 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. At this time there was a great confusion about the nature of light which was solved by de-broglie from where origin of theory of matter wave come into picture. 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 one photon can not be absorbed by more than one electron. Notes for Atomic Structure chapter of class 12 physics. comparing it with y = mx + c, the graph between Kmax and f is a straight line with positive slope and negative intercept. There is no concept of photon conservation. Ex.14 A perfectly reflecting solid sphere of radius r is kept in the path of a parallel beam of light of large aperture. 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. As the maximum kinetic energy just after emission at cathode is , if potential difference across the discharge tube is V then the seed vf with which electrons will reach anode can be given as. email@example.com. 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. What retarding potential is necessary to stop the emission of the electrons ? 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. Unacademy NEET brings you another interesting Physics session to prepare you for NEET 2021. Thus we can say that all the electrons reaching anode will have their speeds distributed from v1 to v2. 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. In equation (1) the second terms on right hand side of equation is , which is the maximum kinetic energy of the ejected electron. no. Sol. 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. 3 Waves in pipes and strings. 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. When light of intensity I falls on a surface, it exerts force on that surface. It posses energy given by. using search above. Tests & Videos, you can search for the same too. the following chapters come under modern physics: Atoms; Nuclei; Semiconductors and devices; Communication systems 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. You can download Free Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes pdf from EduRev by
Those electrons which have high kinetic energies will rush toward, anode and may constitute the current in circuit. Grade 12; PRACTICE. 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. 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. If you want Modern Physics, Chapter Notes, Class 12, Physics (IIT-JEE & AIPMT) | EduRev Notes
This will help a student save time. 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 … (b) Light is incident on the cathode of a photocell and the stopping voltages are measured from light of two difference wavelengths. This is briefly described over here. Download modern abc of physics class 12 pdf document. This potential difference VP1 at which current becomes saturated is called "pinch off voltage". 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. As potential difference increases, space charge decrease and simultaneously the photoelectric current in circuit also increases. By Einstein's energy mass relation, E = mc2 the equivalent mass m of the photon is given by. If an electron (charge = e) is accelerated by a potential of V volts, it acquires a kinetic energy. 2. Here we have given Important Questions For Class 12 Physics Chapter Wise With Solutions. he favours dual nature of light. This minimum frequency or threshold frequency vth can be given as. Consider all cases. 5 Speed of light. RADIOACTIVITY . It has gotten 25010 views and also has 4.8 rating. 4. but, when maxwell asserted that light is a electromagnetic wave, scientists started believing that light is a wave. 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. where p is the momentum of the particle. 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