ICSE Physics Class X (Modern Physics) Important Questions (Unsolved)

Class X
Modern Physics

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.

  1. What is the number of electrons in a neutral atom of this isotope ?
  2. How many protons are there in the nucleus of this atom ?
  3. What is the number of neutrons in the nucleus of this isotope
  4. Do all the isotopes of uranium have the same number of neutrons
  5. What is the number of protons in U238 ?

Q. 3. Ultraviolet light falls on a dry zinc plate.

  1.    Name the particles emitted from the plate.
  2. What is the nature of charge acquired by the plate .
  3. Name the phenomenon that takes place.
  4. Name one of the devices based upon the above phenomenon.

Q. 4. State the mechanism of production of X– rays. Give two important properties of   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 α–particle absorbs an electron. What does it change to ?

Q. 11. A fission reaction is represented as follows :

1H2 + 1H2 –> 2He4 + 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 α–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 β–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.

                            88X226  →  Y  +  α  +  energy

  1. What are the atomic and mass numbers of Y ?
  2. Name the gas formed when the α-particle acquires two electrons.
  3. What is the effect on the motion of the α-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 ZA 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.

  1. Why is the anode of the tube heated up at the time of emission of X-rays ?
  2. How are the strength and penetrating power controlled
  3. 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 ‘β’ particle and then an alpha particle and the resulting nucleus can be represented . What are the value of P and Q in terms of A and Z ?

Q. 22. (i) What is nuclear fusion ?

  (ii) 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) Copy the diagram in your answer book. Draw a pair of plates P1 and P2 to apply electric field, a screen S and an enclosure.

  (ii) What are the functions of A, B, P1, and P2 ?

Q. 32.          β                  γ
 12 Mg 27    →       Al     →
          In the above nuclear reaction

  1. 27Mg12 emits a β-particle and is transformed to aluminium. What is the mass number and the atomic number of aluminium
  2. Aluminium emits a γ-ray. What is the resulting nucleus ? >

Q. 33. State three precautions that must be taken while handling a radioactive source.

Q. 34. Mention two possible sources of background radiation.

Q. 35. An element X changes to another element Y with the emission of beta particles. Write down the equation showing changes in the nucleus. Take the proton number and mass number of X as Z and A respectively.

Q. 36. State briefly two uses of cathode ray tube.

Q. 37. Name the technique used to estimate the age of very old trees, plants, wood and other such specimens. Name the isotope that forms the basis of this technique.

Q.38. Describe briefly, two properties each of alpha particles and gamma radiations.

Q. 39. A mass of lead is embedded in a block of aluminium (2 mm thick). Radiations from a radioactive source incident on the side of the block produce a shadow on a fluorescent screen placed beyond the block. The shadow of the block of aluminium is fainter than the shadow of lead. Give the reson for this difference.

Q. 40. (a) State two factors on which the rate of emission of thermions depends.

(b)The isotope of 92 238  decays by alpha emission to an isotope of Thorium (Th). The thorium isotope decays by beta emission to an isotope of Protactamium (Pa). Write down the equations to represent these two nuclear changes.

(c) Draw a cathode ray tube consisting of a heater, a cathode, a cylindrical anode and a deflecting system. Show how you will connect a low tension battery of 6 V and a high tension one of 1000 v to the electrodes of the tube.

Q. 41. (i) Define the term ‘work function’ of a metal.

(ii) Mention two common properties of gamma radiations and visible light.

Q. 42. (a)

  1. Copy and complete the above diagram by showing and labeling the paths of alpha, beta and gamma radiations in an electric field.
  2. 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 :

              -α                -β                 -β

92P238 …  →    P1…     → …P…  →   …P3 …

Q. 43. How many alpha and beta particles are emitted when uranium
 92 238  decays to lead 82 Pb 206 ?

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 :

  1. moderator
  2. control rods
  3. 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 U-235 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 :

  1. One electron ;
  2.   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 :

  1.  An alpha particle ;
  2. A beta particle.
  3. Explain why alpha – and beta- particles are deflected in an electric

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