2.Define threshold wavelength for photoelectric effect? Ans.Electrons are accelerated by a voltage, V= 50 kV =. Practical Physics. The best app for CBSE students now provides Dual Nature of Radiation and Matter class 12 Notes latest chapter wise notes for quick preparation of CBSE board exams and school-based annual examinations. Hence explain why a fast neutron beam needs to be the rmalised with the environment before it can be used for neutron diffraction experiments. 7.Draw a graph showing the variation of stopping potential with frequency of the incident radiations. Ans. (c) How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon? Thus, saturation current is independent on the frequency of incident light. Work Function (φ) of Some Elements Given in Brackets : (Quantum theory of light) we can explain above failures of classical physics. De Broglie wavelength is given by the relation: This wavelength is nearly 105 times less than the wavelength of yellow light. When quinine sulphate is illuminated with ultraviolet or violet light it gives out blue light. De Broglie proposed that if the radiations could possess dual nature, matters could also possess dual nature. The transitions of electrons from various outer shells to the innermost ‘K’ shell produces a group of X-rays lines called as K-series. Atoms ( All ) Select Topic. Hence, the high-energy neutron beam should first be the rmalised, before using it for diffraction. They are fluorescent materials. In the relativistic limit, the total energy is given as: 13. of emitted electrons be greater? Save my name, email, and website in this browser for the next time I comment. Ans.Energy flux of sunlight reaching the surface of earth, Hence, power of sunlight per square metre, P W. Average wavelength of photons present in sunlight, Number of photons per square metre incident on earth per second = n. Hence, the equation for power can be written as: Therefore, every second, photons are incident per square metre on earth. The gold leaf having the same charge as the metal stem gets repelled and move away as shown in the figure. Why do all photoelectrons not come out with the same energy if incident radiation is monochromatic? Question: Monochromatic light of wavelength 632.8nm is generated by a helium-neon laser having power of 9.42mW. Does sodium show photoelectric emission for light on the velocity of photoelectrons? The stopping potential (and hence the maximum kinetic energy of emitted electrons) is independent of the intensity of light but that the saturation current (and hence the number of emitted photoelectrons) is proportional to the intensity. Since, the photocell will not respond to the red light produced by the laser. What is its unit? Previous Year Papers. Calculate the following: a) maximum kinetic energy of the electrons emitted, b) stopping potential, and c) maximum speed of the emitted electrons. Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. Find the change in the following: a) Saturation current (i), and b) work function of metal. Photoelectric emission is an instantaneous process, meaning there is no time lag between the incident light and the emission of free electrons (photoelectrons). In addition to characteristic X-rays tubes emit a continuous spectrum also. Hg, are called cathode rays. An electron and a photon each have a wavelength of 1.00 nm. (a) maximum kinetic energy of the emitted electrons. Light of wavelength 488 nm is produced by an argon laser which is used in the photoelectric effect. Ans.Wavelength of light of a sodium line, = 589 nm m. (a) For the kinetic energy K, of an electron accelerating with a velocity v, we have the relation: We have the relation for de Broglie wavelength as: Substituting equation (2) in equation (1), we get the relation: Hence, the kinetic energy of the electron is J or 4.31. However, stopping potential got higher in the negative direction for higher values of frequency of absorbed light. and wavelength of such radiation is continuous because the loss in energy is statistical. The energy of each electron is equal to its kinetic energy, i.e.. Hence, photo-energy is given as: Hence, the new stopping potential is 1.50 eV. (b) In a plot of photoelectric current versus anode potential, how does. As you have seen in Exercise 11.31, an electron beam of this energy is suitable for crystal diffraction experiments. 16.In an accelerator experiment on high-energy collisions of electrons with positrons, a certain event is interpreted as annihilation of an electron-positron pair of total energy 10.2 BeV into two rays of equal energy. See answers at the end to know what ‘very high speed or energy’ means. According to which, when a monochromatic beam of X-rays (wavelength λ, ) strikes the electron in a carbon target, two types of X-rays are scattered. of photon) is given by, is taken to be equal to Z – σ, where Z is proton number or atomic number of the element and σ is called the. (b) (i) Saturation current depends only on the intensity of incident radiation but is independent of the frequency of incident radiation. The first discovery of this phenomenon was made by Hertz. Find the typical de Broglie wavelength associated with a He atom in helium gas at room temperature and 1 atm pressure; and compare it with the mean separation between two atoms under these conditions. What is the velocity of the effected photoelectron? are taken to be roughly the same, how does the resolving power of an electron microscope compare with that of an optical microscope which uses yellow light? Hence, we assume the dual nature of light. The spacing and dispositions of atoms of a crystal can be precisely determined by using. So, photoelectric current gets doubled. Characteristic X-rays and Continuous X-rays. 8. (b) The energy of a photon is given by the relation: Therefore, the energy of the photon is 1.243 keV. 2.Mention one physical process for the release of electron from the surface of a metal? 6.Show graphically how the stopping potential for a given photosensitive surface varies with the frequency of incident radiations? The power emitted is 9.42 mW. The maximum kinetic energy of the photoelectrons varies linearly with the frequency of incident radiation but is independent of its intensity. It intersects the at Hz, which is the threshold frequency of the material. 2. (c)Momentum of the hydrogen atom is the same as the momentum of the photon. Ans.Photoelectric cut-off voltage, = 1.5 V. The maximum kinetic energy of the emitted photoelectrons is given as: Therefore, the maximum kinetic energy of the photoelectrons emitted in the given experiment is J. Ans. Do you see what is wrong? Assume that the photons in the sunlight have an average wavelength of 550 nm. However, photoelectric effect verifies the particle nature of radiations. (Rest mass energy of electron = 0.511 MeV.). Speed of the bullet, v= 1.0 km/s = 1000 m/s. 11. Ans. The experimental setup for the experiment is shown below: Evacuated chamberfor the free movement of electron without any air resistance, BatteryUsed for the acceleration of electrons inside the cylinder. Ans.Wavelength of the monochromatic light, = 632.8 nm m. (a)The energy of each photon is given as: (b)Number of photons arriving per second, at a target irradiated by the beam = n. Assume that the beam has a uniform cross-section that is less than the target area. The notes are based on CBSE Syllabus. Dual Nature of Matter and Radiation. Electrons are collected at anode A, constituting a current in the circuit. Calcium sulfide and barium sulphide, after absorbing sunlight, produce blue phosphorescence for some time. In the above formula, the expression for energy can only be used in the non-relativistic limit, i.e., for v << c. When very high speeds are concerned, the relativistic domain comes into consideration. Some metals like zinc, magnesium etc. that photoelectric current increases as we increase the intensity of light & obtain saturation value at larger value of potential difference V between cathode & anode. (ii) Stopping potential does not depend on the intensity of incident radiations. Electrons with a maximum speed of m/s are ejected from the surface. 26.The wavelength of a probe is roughly a measure of the size of a structure that it can probe in some detail. 2. Dual nature of radiation Previous JEE Mains Papers questions and solutions Download Pdf By eliminating v & φ from equation (4) to (6), we obtain. Light of frequency 1.9 times the threshold frequency is incident on a photosensitive material. They are not deflected by electric or magnetic field. This is because the mass of a microscopic object is very small, so wavelength becomes sufficiently large andhence, observable. Is photoelectric emission possible at all frequencies? PHOTOELECTRIC EFFECT AND WAVE THEORY OF LIGHT: WAVE NATURE OF MATTER: DE BROGLIE’S HYPOTHESIS: Your email address will not be published. Germer (1896-1971). Evaluate the following: a) energy and momentum of each photon, b) The number of photons emitted per second, and c) speed of a hydrogen atom to have momentum equal to that of an emitted photon by the laser. 25.An electron microscope uses electrons accelerated by a voltage of 50 kV. And while interacting with matter, it behaves as a particle, Photons of similar frequencies possess equal energies and equal momentums, Photons are electrically neutral (not having a net positive or negative charge). System of particles and Rotational Motion, Semiconductor Electronics : Materials, Devices and Simple Circuits, Please fill in the details for Personalised Counseling by Experts, Not found any post match with your request, Can not copy the codes / texts, please press [CTRL]+[C] (or CMD+C with Mac) to copy, Join IIT JEE & NEET Online Courses at CLEAR EXAM. Each energy quantum has a value equal to, These specific packets of quanta of energy are known as photons, The above equation is known as Einstein’s photoelectric equation, Since saturation current is just a maximum value of photoelectric current, saturation current gets higher with increasing intensity of incident light. Hence define threshold frequency? Find the (a) Maximum frequency, and (b) Minimum wavelength of X-rays produced by 30 kV electrons. Hence, the inter-atomic spacing is about a hundred times greater. a) Using Einstein’s photoelectric equation: Kmax = hv – Φo = (6.6×10-34×6×1014)J – (2.14×10-19)J. b) Stopping potential is given by the equation: c) Maximum speed of emitted electrons can be found using maximum kinetic energy equation: 2)Question: Light of wavelength 488nm is incident on an emitter plate. The existence of a minimum quantum of energy can be ignored and the total energy of a radio wave can be treated as being continuous. Case-2-When collector plate was kept at lower potential (retarding potential) with respect to the emitter. (a) Quarks inside protons and neutrons carry fractional charges. For a given K.E. One important feature of continuous X-rays is that they end abruptly at a certain lower wavelength for a given voltage. Experiments of this kind on Na, Li, K, etc. Number of photons emitted per second (n) will be given by the equation: To find the speed of a hydrogen atom (v) to have momentum same as a photon: Here, p = momentum of photon =1.043×10-27kgm/s, and, Question: An electron has a kinetic energy of 120eV. Notes offered by thinkIIT is helpful in securing good marks in class 12 Revision notes Chapter. Absorption of ultraviolet radiation, = 330 nmm Photocurrent versus intensity of could... Depends upon threshold frequency depends on the other hand, the de Broglie wavelength a! Elements as target in the wave-picture of radiation and Matter notes photoectrons i.e Patro PGT are. 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