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Hitesh Nair
St. Thomas Residential School, Thiruvananthapuram

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Which one is unstable amongst proton, neutron, electron and alpha-particle? Can it be concluded from beta decay that electrons exist within the nucleus? No. The beta particle, although an electron, is actually created at the instance of beta decay and is ejected at once. In beta decay, a neutron splits to form a proton and an electron (beta particle). How is a cathode ray beam affected while passing through i) a magnetic field ii) an electric field? 1. The beam will be deflected in a direction normal to both the direction of the magnetic field and the direction of its motion, as indicated by Fleming s left hand rule. This deflection is by Lorentz s force. The path followed by it shall be circular. 2. A cathode ray beam while passing through an electric field is deflected towards the positive plate due to force of attraction. The path followed by it shall be parabolic. Why are gamma rays emitted only in nuclear processes and not in orbital electron transitions? The energy of gamma rays is of the order of MeV. Energies of this magnitude occur in nuclear processes only occur in nuclear changes, not in orbital electron transmissions. How is the radioactivity of an element affected when it forms chemical compounds? The radioactivity is not affected in any way. Chemical bonds involve only orbital electrons, whereas radioactivity is a nuclear phenomenon. When a nucleus undergoes alpha decay, is the product atom electrically neutral? What about in beta decay? No, in alpha decay, the two protons from the nucleus are lost. Thus the atom is left with two extra electrons. It therefore, has a double negative charge. In beta decay, the atom is left with a net positive charge. State the kind of nuclear reaction taking place in a nucleus during the emission of a -particle. During emission of a -particle from the nucleus, a neutron changes into a proton by emitting a beta particle and anti-neutrino as follows: 0n1 1p1 + -1e0 + v So, in the nucleus, the number of the neutrons decreases by 1 with the emission of a -particle and the number of proton increases by one. The sum of protons and neutrons, i.e., atomic mass remains the same but the atomic number increases by one. Is it possible for hydrogen atom isotope to emit alpha particle? Explain. No. This is because alpha particle consists of two protons and two neutrons. However, none of the isotopes of hydrogen has the requisite number of protons and neutrons in its nucleus to emit an alpha particle. Thus they cannot emit alpha particles. Explain why: Beta particles are deviated to a greater extent in a magnetic field than alpha particles. Gamma rays are not deflected in an electric field. Explanation: 1. Beta particles have a negligible mass compared to alpha particle. So, they are easily attracted and experience greater deflection. 2. Gamma rays are electrically neutral, so they are not deflected Explain why radium paint consisting of zinc sulphide and a trace of radium salt, glows in the dark. The radium in the radium salt will emit alpha particles due to radioactive decay. When these alpha particles strike the zinc sulphide, fluorescence occurs. This is the source of the glow-in-the-dark effect. What is Carbon-14 dating? C-14 is an isotope of carbon found in the atmosphere due to bombardment of 7N14 with a neutron. 7N14 + 0n1 6C14 + 1H1 (proton) Living plants absorb carbon dioxide from the atmosphere which contains a constant quantity of C14. When a plant dies and begins to decay, it no longer takes in any C-14. C-14, being radioactive, begins to decay with the emission of -particles. So the amount of C-14 keeps on decreasing at a fixed rate over time. Thus, by comparing the amount of C-14 in the plant at present, and the amount of C-14 in the plant when it was alive, the age of the specimen can ascertained. What is the photo-electric effect ? When a light of suitable wavelength or frequency is incident on a metal surface, the emission of electrons takes place. This phenomenon is known as the photo-electric effect. What is a diode? Why is a diode called a valve? A diode consists of two electrodes i.e. a cathode (the filament) and the anode (the plate). It is called a valve because it allows current to flow in only one direction. It is similar to the valve in the human heart, which prevent the flow of blood in the reverse direction. Is the electron-volt a unit of charge, potential difference or energy? Electron-volt is a unit of energy. What is the difference between an electron and a -particle? There is no difference between an electron and a -particle. -particle is just the name given to an electron emitted from the nucleus of an atom. If a person stands between an X-ray tube and a fluorescent screen, what is observed on the screen? If a person stands between an X-ray producing tube and a fluorescent screen, the shadows of bones are seen on the screen. This is because bones absorb more X-rays than the flesh does. A radioactive substance is oxidized. What change would you expect to take place in the nature of its radioactivity? There will be no change in the nature of its radioactivity. This is because radioactivity is a nuclear phenomenon and oxidation does not affect the nucleus of the substance. State one industrial use of , and radiations. -particles The ionizing effect of these particles is used in industry for making certain luminescent signs and batteries. -particles These are used to produce X-rays. -particles They are used to initiate nuclear reactions. They can also knock out electrons from the surface of a metal, on which they are allowed to fall. Why is it advisable to view a TV screen from a distance of about 12 feet? In a TV set, electrons are accelerated by about 20 kV and strike the screen due to which mild X-rays are produced. The X-rays can seriously damage our body. However, these X-rays are absorbed by a length of few feet of air due to ionization by collisions. It is hence advisable to view a TV screen from a distance of about 12 feet. Why are -particles not used in radiotherapy? -particles have a very small penetrating power and hence they cannot enter the skin. Is an indirectly heated cathode better than a directly heated one? If so, why? Yes. The indirectly heated cathode can be coated with oxides of alkali metals which have a very low work function. It gives an abundant supply of electrons even at moderate temperatures of about 1000oC. When does the nucleus of an atom become radioactive? This happens when the number of neutrons in a nucleus far exceeds the number of protons in it. The nucleus becomes heavy and unstable, leading to the release of radiation.

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