(a) Find the energy and momentum of each photon in the light beam, (b) How many photons per second, on the average, arrive at a target irradiated by this beam? Ans. 7.Draw a graph showing the variation of stopping potential with frequency of the incident radiations. Experiments of this kind on Na, Li, K, etc. Greater intensity at a particular frequency means greater number of photons per second absorbed & consequently greater number of electrons emitted per second & so greater current. Apply quantum ideas for understanding the operation and working principle of optoelectronic devices. See answers at the end to know what ‘very high speed or energy’ means. Therefore, the product (phase speed) has no physical significance. (e) The absolute value of energy of a particle is arbitrary within the additive constant. This change in wavelength i.e. When light from this spectral line is incident on the emitter, the stopping (cut-off) potential of photoelectrons is 0.38 V. Find the work function of the material from which the emitter is made. And the electrons released due to photoelectric effect are called photoelectrons, Evacuated tube consist of photosensitive plate (emitter) and the metal plate (collector), so that electrons could freely flow from emitter to collector without any air resistance, Photosensitive plate (emitter) to absorb visible light and emit electrons, Metal plate (collector) to receive electrons emitted from the emitter, thus constituting a photoelectric current flow from collector plate to the emitter plate (opposite to the flow of electrons), Monochromatic light of short wavelength (meaning high frequency), Battery to accelerate emitted electrons through a potential difference, Voltmeter to measure the potential difference between the emitter and the collector plates due to photoelectric current flow. Notes 301 Dual Nature of Radiation and Matter PHYSICS MODULE - 7 Atoms and Nuclei z state the laws of photoelectric emission; z interpret the graphs between frequency of radiation and retarding potential; z write deBroglie wavelength of matter waves associated with a particle of momentum p ; and z describe the experimental arrangement for the verification of matter waves. : Since X-rays can penetrate through various materials, they are used in industry to detect defects in metallic structures in big machines, railway tracks and bridges. The force exerted on the electron is given as: θ = Angle between the magnetic field and the beam velocity. Ans. Derive an expression for debroglie wavelength of an electron? To derive the Compton shift. 4. An electromagnetic wave of wavelength is incident on a photosensitive surface of negligible work function. 5. What is the kinetic energy of (a) fastest (b) the slowest photoelectron? Kinetic energy (K) and velocity (v) are related as: De Broglie wavelength and velocity (v) are related as: Using equation (2) in equation (1), we get: Hence, the kinetic energy of the neutron is J or eV. The X-rays were discovered by Prof. Roentgen, a German scientist in 1885. The energy emitted by a photon is given as: Let n be the total number of photons falling per second, per unit area of the pupil. Is photoelectric emission possible at all frequencies? Their KE ranges from zero to E. which depends on frequency of incident radiation and nature of cathode. Do you see what is wrong? The wavelength of the sodium light is 589 nm. Therefore, fractional charges may exist in nature; observable charges are still the integral multiple of an electrical charge. The above three inconsistencies showed that wave theory of light could not explain the experimentally observed characteristics of photoelectric effect. The characteristic X-rays spectra helps us to identify the element of target material. Then, is coefficient of viscosity of air, r is radius of drop and v, In fig. 14. If the whole of the energy is converted to continuous radiation, then λ. If other factors (such as numerical aperture, etc.) (a) Obtain the de Broglie wavelength of a neutron of kinetic energy 150 eV. Previous Year Papers. (e) The energy and momentum of an electron are related to the frequency and wavelength of the associated matter wave by the relations: But while the value of is physically significant, the value of (and therefore, the value of the phase speed ) has no physical significance. Hallwach and Lenard during 1886-1902, researched the process of photoelectric emission. Dual Nature Of Radiation And Matter pdf notes, Your email address will not be published. Since wave theory could not explain the photoelectric effect, Einstein proposed a particle theory of light for the first time, He said that radiations are made up of specific and discrete packets of energy called as quanta of radiation energy. Average energy of a gas at temperature T, is given as: Mean separation between two atoms of the gas is given by the relation: Hence, the mean separation between the atoms is much greater than the de Broglie wavelength. (c) a dust particle of mass kg drifting with a speed of 2.2 m/s? ), the electron may escape from the surface. Class 12 NCERT/CBSE board notes for Dual Nature Of Matter And Radiation. Hence, the amount of energy absorbed per second per electron is: Time required for photoelectric emission: The time required for the photoelectric emission is nearly half a year, which is not practical. Photoelectric emission takes place when a light of frequency 6×1014 Hz is incident on the metal surface. If each of these metals is exposed to radiations of wavelength 3300nm, which of these will not exit photoelectrons and why? 10. 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. Some metals like zinc, magnesium etc. Atoms ( All ) Select Topic. The first type of scattered wave has same wavelength (λ, ) as the incoming X-rays, while second type has a longer wavelength (λ) than incident rays (First type of X-rays are called unmodified x-rays, while second type of X-rays are called modified X-rays.) The wavelength associated with electron is quite large and is experimentally observable. 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. In this treatment, the photon is assumed as a particle of energy, Further, the rest mass of photon is zero (because photon travels with the speed of light) hence the momentum of photon can be written as. Hertz, in 1887 discovered the phenomena of photoelectric effect for the first time, As he was experimenting on the generation of electromagnetic waves by spark discharge, he noticed that sparks around the detector loop were intensified when ultraviolet radiation fell on the emitter plate. Calculate the work function of the emitter plate. Variation of photoelectric current with the frequency of incident light: Exercise: ( Dual Nature Of Radiation And Matter ). 28.Compute the typical de Broglie wavelength of an electron in a metal at and compare it with the mean separation between two electrons in a metal which is given to be about. … (a) What is the energy per photon associated with the sodium light? 12. The photons. Further with the analogy of photon, the frequency of matter waves is. 5.Ultraviolet light is incident on two photosensitive materials having work function and ( > ). It was also found that, after reaching a certain minimum frequency value, stopping potential followed a linear relationship with the frequency of incident light. Ans.An X-ray probe has a greater energy than an electron probe for the same wavelength. When quinine sulphate is illuminated with ultraviolet or violet light it gives out blue light. The house hold tubes are painted from inside with magnesium tungstate or zinc-beryllium silicate. Dual Nature Of Radiation And Matter Photoelectric emission is an instantaneous process, meaning there is no time lag between the incident light and the emission of free electrons (photoelectrons). But, alkali metals like sodium potassium etc. De Broglie wavelength of an electron is given as: Hence, the de Broglie wavelength is much greater than the given inter-electron separation. Click here. It also is a spectrum consisting of radio waves, microwaves, infrared waves, visible light, ultraviolet radiation, X-rays, and gamma rays. Take the area of the pupil to be about 0.4 cm2, and the average frequency of white light to be about . Find the (a) Maximum frequency, and (b) Minimum wavelength of X-rays produced by 30 kV electrons. Radiation can behave as a wave as well as a particle under different situations. This was the third inconsistency with the experiments. Work Function (φ) of Some Elements Given in Brackets : (Quantum theory of light) we can explain above failures of classical physics.
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