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| Nuclear Energy and Chemical Energy |
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| Nuclear energy is released when very small particles of matter split or combine. After the split or combination, they result in small particles or heavy particle. The rest of the mass is changed into energy. This process of changing mass into energy produces the energy. |
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| Energy can also be stored in matter as chemical energy, which depends on how the particles of matter are arranged. Therefore, chemical energy depends on the positions of objects and is a form of potential energy. |
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| Radioactive materials always carry this international warning symbol. |
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| State one way of producing a beam of electrons and define the phenomenon. |
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| Thermionic emission. |
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| Thermionic emission is the phenomenon by which free electrons from surface of a metal are emitted when heated to a high temperature. |
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| What are Cathode rays? Give three properties of these rays. |
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| Cathode rays are a beam of electrons emitted from a hot cathode. |
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| Properties: |
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 They are deflected by magnetic field. |
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 They are deflected by electric field. |
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 They produce fluorescence on certain materials such as Zinc Sulphide. |
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| Name a metal most suitable for the production of thermions giving reasons. How can the rate of emission be increased? |
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| Tungsten is the metal. |
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| Has a high melting point of about 3655 K and a work function of 4.5 eV, emission starts at 2500 K. The rate of emission can be increased by coating the tungsten surface with barium and strontium oxide. Reduces the work function to 1 eV. Emission at good rate starts when heated to 1000 K. |
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| How do infrared and g - rays differ in their |
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| (i) wavelength and |
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| (ii) penetrating power. |
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| (i) g - rays have much shorter wavelengths of the order of 10-13 m while the infrared have longer wavelengths of the order of 10-6 or more. |
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| (ii) g - rays have a much higher penetrating power as compared with infrared rays. |
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| Cathode rays and b - rays both are electrons. How do they differ from each other? |
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| (i) b - rays are electrons emitted from the nucleus of an atom while cathode rays are electrons emitted from the outer orbits of the atom. |
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| (ii) b - rays travel with very speeds of the order of 2.7 x 108 m/s while the cathode rays travel with much lesser speeds. |
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| (Of the 2 differences, first one is more important) |
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| A certain nucleus X has a mass number of 15 atomic number 7. Find the no. of neutrons. The nucleus X loses (i) one proton, (ii) one b - particle, (iii) one a - particle. Express each change and write a symbol of the new nucleus in each case. |
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| No. of protons = mass no. - atomic no. |
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| = 15 - 7 |
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| = 8 |
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Element X can be written as  |
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| (i) Loss of 1 proton cause mass number and atomic number each to reduce by 1. The change can be written as |
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| X changes to Y. |
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| (ii) Loss of one b - particle |
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| Mass number remains the same, atomic number increases by 1. |
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(iii) Loss of one a - particle.  decrease in mass number is 4 and decrease in atomic number is 2. |
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| Calculate the energy released when 1 kg mass is completely converted to energy (C = 3 x 108 m/s). |
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| Complete the following fission reaction: |
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| What should be the value of x? Is the mass conserved? Explain. |
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| x = 3 |
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| Mass is not conserved. The difference in mass is converted to energy as the binding energy of the nuclides changes. |
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| What is the function of control rods in a nuclear reactor? Explain, what is the material used for these rods? |
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| Control rods regulate the rate of fission by absorbing the excess neutrons and prevent the chain reaction. Deeper the rods are placed slower the process. |
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| The material used is boron or cadmium alloyed with aluminium or steel. |
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| What is the function of a moderator, name the material. |
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| Moderator slows down the neutrons released during fission. Fast moving neutrons can escape passing through the nucleus hence they have to be slowed down so that the nucleus captures the neutron and causes fission. |
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| Graphite is used as moderator. |
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