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Q. 1. (i) What is thermionic emission (ii) Name two factors on which the rate of emission of thermions depend. Q. 2. What is an isotope ? One isotope of uranium has a mass number of 235 and an atomic number of 92. i. What is the number of electrons in a neutral atom of this isotope ? ii. How many protons are there in the nucleus of this atom ? iii. What is the number of neutrons in the nucleus of this isotope iv. Do all the isotopes of uranium have the same number of neutrons v. What is the number of protons in U238 ? Q. 3. Ultraviolet light falls on a dry zinc plate. i. Name the particles emitted from the plate. ii. What is the nature of charge acquired by the plate . iii. Name the phenomenon that takes place. iv. Name one of the devices based upon the above phenomenon. Q. 4. State the mechanism of production of X rays. Give two important properties o X ray. Q. 5. What is the photoelectric effect ? Draw a neat labelled diagram of a photoelectric cell. (out of course) Q. 6. (i) Define nuclear fusion and state the necessary conditions for the same . (ii) Name two factors on which the rate of emission of thermions depend. Q. 7. Why is diode called a valve ? Q. 8. Draw a neat labelled diagram of modern X ray tube. Q. 9. What is the mechanism of energy production in a fission reaction ? Q. 10. An particle absorbs an electron. What does it change to ? Q. 11. A fission reaction is represented as follows : 2 2 4 1H + 1H --> 2He + x Identify x. Q.12. (i) Draw a neat labelled diagram of a hot cathode ray tube. (ii) What is the effect on the beam particles if (a) a hotter filament is used ? (b) the anode voltage is increased ? (iii) Name one device in which the cathode ray tube is used. Q.13. State the factors that affect the rate of emission of electrons in a photoelectric cell. Q.14. (i) A thorium isotope 233Th90 undergoes an decay and changes to radium. What is the atomic number and mass number of radium produced? (ii) If the radium undergoes a further disintegration and emits two particles, represent the reaction in the form of an equation. (iii) What is the source of energy released during the decay ? Q.15. In the nuclear reaction given below, nucleus X changes to another nucleus Y. 226 Y + + energy 88X i. What are the atomic and mass numbers of Y ? ii. Name the gas formed when the -particle acquires two electrons. iii. What is the effect on the motion of the -particle when it passes through a region containing a magnetic field ? Q.16. What is a rectifier ? Give a reason why the diode valve is used as a rectifier. Q.17. What is the main difference between fission reaction and fusion reaction ? Give one example of each. Q.18. An atomic nucleus denoted by ZXA emits an alpha particle. Write an equation to show the formation of the daughter product. Q.19. X-rays are produced in a Coolidge tube when cathode rays are made to strike a target. i. Why is the anode of the tube heated up at the time of emission of X-rays ? ii. How are the strength and penetrating power controlled iii. Which of the soft and hard X-rays have longer wavelength and which has higher penetration power ? Q. 20. What is a photoelectric effect ? On what property of incident radiation does it depend to obtain photoelectric current ? Q. 21. a radioactive element X first emits a particle and then an alpha particle and the resulting nucleus can be represented PYQ. What are the value of P and Q in terms of A and Z ? Q. 22. (i) What is nuclear fusion ? (ii)0 name the particle which cause nuclear fission of U-235. Q. 23. What is a diode ? Why is a diode called a valve ? Q. 24. What is radioactivity ? Q. 25. a radioactive substance is oxidized. What change would you expect to take place in the nature of its radioactivity ? Give a reason for your answer. Q. 26. What are beta rays and gamma rays ? Q. 27. Explain briefly what change takes place within the nuclei, when beta particles are emitted by a radioactive substance. Q. 28. Name the particles given out during radioactive decay. Q. 29. Show by equations, the effect on the proton number Z and mass-number A of the parent nucleus brought about by the two types of radioactive decay. Q. 30. What is Carbon-14-dating ? Q. 31. The following diagram is of the simplified version of an electron-gun which is an integral part of a cathode ray-tube, A is a filament and B is a metal cylinder i. ii. Copy and complete the above diagram by showing and labeling the paths of alpha, beta and gamma radiations in an electric field. iii. Name the radiations which have the least penetrating power. (b) (i) Give one difference between a chemical change and a nuclear change. (ii) How is a cathode ray tube used to convert an electrical signal into a visual signal ? (c) Copy and complete the following nuclear equations by filling the correct values in the blanks : - - - 238 92P P1 P2 P3 Q. 43. How many alpha and beta particles are emitted when uranium 238U92 decays to lead 206Pb82 ? Q. 44.With the help of an equation, state the mechanism of energy production in a nuclear fusion reaction. Q. 45. State the functions of the following in a nuclear reactor : i. moderator ii. control rods iii. coolant. Q. 46. (i) Mention two important precautions that should be taken while handling radioactive materials. (ii) State one use of radio-isotopes. Q. 47. (i) Draw a labelled diagram of a hot cathode ray tube. (ii) Why are the materials of low work function preferred as thermionic cathode materials ? (iii) Write an equation to show the fission of a nucleus of U235 with the production of three neutrons. Q. 48. A certain radioactive nucleus emits a particle that leaves its mass unchanged but increases its atomic number by one. Identify the particle and write its symbol. Q. 49. What is nuclear chain reaction ? Q. 50. (i) Name the material used for making the control rods in a nuclear fission reaction. Why is the material named by you suitable for this purpose ? (ii) State one difference and one similarity between a nuclear bomb and a nuclear reactor. Q. 51. (i) Define thermionic emission. (ii) Mention one use of thermionic emission. (iii) Name a substance which is a good thermionic emitter. Q. 52. State three properties that are common to and shown by both beta rays and cathode rays. Q. 53. What will an alpha particle change into when it absorbs : i. One electron ; ii. Two electrons ? Q. 54. Mention two important properties of a metal that make it a good thermionic emitter. Q. 55. Name the three main parts of a cathode ray tube. Mention one important function of each of the three main parts. Q. 56. (i) State the principle on which the functioning of a nuclear reactor is based . (ii)Name the material that can be used as fuel in a nuclear reactor. (iii) How is the activity in a nuclear reactor controlled ? Q. 57.(i) What happens to the atomic number of an element when it emits : i. An alpha particle ; ii. A beta particle. iii. 0 Explain why alpha and beta- particles are deflected in an electric
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