Modern Physics – Some points to remember

  • The first scientific theory about the constituents of matter was given by John Dalton in 1803.
  • In 1815, Prout proposed that atoms of all elements were made up of hydrogen atoms.
  • J.J. Thomson in 1910 conducted an experiment by passing electricity through gases at reduced pressure. This experiment showed the existence of negatively charged particles in an atom. He named these particles as ‘electrons’.
  • J.J. Thomson’s atom model is referred to as the Plum-Pudding model.
  • Neil Bohr, a Danish physicist in 1913, presented an improved atom model.
  • The atomic nucleus was discovered in 1911 by Rutherford and his associates as a result of their experiment on scattering of alpha particles by thin gold foils.
  • The total number of nucleons (protons and neutrons) in the nucleus of the atom is called the mass number of the atom and is denoted by A.
  • The total number of protons in the nucleus of an atom is called the atomic number of the atom and is denoted by Z.
  • The operating nuclear power reactors in India are at Kalpakkam (Tamilnadu), Kakrapara (Gujarat), Kaiga (Karnataka), Tarapur (Maharashtra) and Kota (Rajasthan).
  • The process in which two or more light nuclei fuse together to form a heavy nucleus is called nuclear fusion.
  • The phenomenon of breaking up of a heavy nucleus into two or more lighter nuclei of comparable masses is called nuclear fission.
  • The reactors which produce their own fuel during their operation are called breeder reactors.





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