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ICSE Notes 2016 : Physics (Vidya International School (VIS), Yeola)

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Question Bank Producing and Using Stream of Electrons 1. (a) What do you understand by the following terms : (i) Free electrons, (ii) Thermions ? (b) State one way by which thermions differ from free electrons. Ans.(a) (i) Free electrons : The electrons, revolving in the outermost orbit of an atom, which are weakly held by the nucleus are called free electrons. (ii) Thermions : The electrons emitted from the surface of a metal, when heat energy is supplied to the metal are called thermions. (b) Whereas free electrons are free in a sense that they can move in the metals in any direction, the thermions completely break loose from the metal surface due to the absorption of heat energy. 2. What do you understand by the following terms? (i) Space charge (iii) Electron volt (ii) Threshold energy or work function (iv) Threshold temperature. Ans. (i) Space charge : The space around cathode which is filled with free thermions is called space charge. (ii) Threshold energy or work function : The minimum heat energy required to make a metal emit an electron (thermion), from its surface is called threshold energy or work function. Class-X 1 Question Bank

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