Nuclear Physics and Electronics

 Atomic and Nuclear Physics


Proton was discovered by Rutherford when he bombarded the nitrogen nuclei with alpha particle.
The charge on a proton is +1.6× 10-19


Neutron was discovered by J.Chadwick when he bombarded with berrylium with alpha particles.
Cathode Rays
Cathode rays, discovered by Sir William Crooke and its properties are
  • travel in straight lines.
  • Produce fluorescence.
  • can penetrate through thin foils of metal and deflected by both electric and magnetic fields.
  • have velocity ranging 1/30th to 1/10th of the velocity of light.
Positive or Canal Rays
  • These rays were discovered by Goldstein.
  • The positive ray consists of positively charged particles.
  • These rays travel in straight line.
  • These rays are deflected by electric and magnetic fields.
  • These rays can produce ionization in gases.


  • The spontaneous process by which a nucleus changes with the emission of some particle or radiation.
  • Radioactivity was discovered by Henry Becquerel, Madame Curie and Pierre Curie for which they jointly won Nobel Prize.

Nuclear Fission

  • The process of the splitting of a heavy nucleus into two or more lighter nuclei is called Nuclear Fission.
  • Nuclear fission was first demonstrated by Halin and Fritz Strassmann.
  • Atom Bomb is based on nuclear fission. U235 and Pu239 are used as fissionable material.
  • If the particle starting the nuclear fission is produced as a product and further takes part in the nuclear fission reaction then the chain of fission reaction is called chain reaction. It can be divided into two parts:
  1. Controlled chain reaction.
  2. Uncontrolled chain reaction.

Nuclear Reactor or Atomic Pile

  • Nuclear reactor is an arrangement, in which controlled nuclear fission reaction takes place.
  • First nuclear reactor was established in Chicago University under the supervision of Prof Enrico Fermi.
  • Nuclear reactor in which Uranium is used as fuel is called thermal reactors.
  • Nuclear reactor in which Plutonium is used fuel is called breeder reactor.
  • Heavy water, graphite and beryllium oxide are used to slow down the fast moving neutrons. They are called moderate.
Uses of Nuclear Reactor
(i)To produce electrical energy from the energy released during fission.
(ii)To produce different isotopes, this can be used medical, physical and agriculture science.
There are several components of nuclear reactor which are as follows:
  • Fissionable Fuel is the material which is used for the fission e.g. U235 or U239  etc.
  • Moderator are used to slow down the high speed neutrons. e.g Heavy water, graphite and beryllium oxide.
  • Coolant are used to remove the heat generated in the fission process. e.g. cold water, liquid hydrogen.
  • Control rods are good absorber of neutron so they are used to control the fission reaction. When the reactor is to be started cadmium rod are pulled out and any neutron present in the nuclear reactor starts fission.
Nuclear Fusion
  • When two or more light nuclei combined together to form a heavier nucleus is called as nuclear fusion.
  • For the nuclear fusion, a temperature of the order of 108 K is required.
  • Hydrogen Bomb was made by the American Scientist in 1952. This is based on nuclear fusion. It is 1000 times more powerful than atom bomb.
Einstein's Mass -Energy Relation:
  • According to Einstein's theory when there is a loss of Δm mass, the energy produced is given by E=mc2  , 
here E= energy released, c= speed of light in vaccum.
  • The minimum energy required to separate the nucleons upto an infinite distance from the nucleus is called nuclear binding force.
Photoelectric Effect:
  • The rate of emission of photo electrons from the a metal surface is directly proportional to the intensity of incident light.
  • The maximum kinetic energy of photoelectric does not depend on the intensity of incident light.
  • Maximum kinetic energy of emitted photoelectric increases with the increase in frequency of incident light.
  • If the frequency of incident light is below than a certain minimum value called threshold frequency then no emission of photo electrons takes place from the metal surface.
  • There is no time lag between the incidence of light and emission of photo electrons from the metal surface.
Electromagnetic Waves:
  • Electromagnetic waves are those waves in which electric and magnetic field vectors changes sinusoidally and are perpendicular to each other as well as perpendicular to the direction of propagation of wave.
  • These waves are produced by the accelerating charge particles.
  • These waves  are transverse in nature and do not require any medium for propagation.
  • X-rays are electromagnetic waves with wavelength range 0.1 A-100 A.
  • X-rays were discovered by Roentgen.
  • X-rays travels in straight line.
  • Long exposures of X – rays in injurious for human body.
  • X – rays shows photoelectric effect.
Uses of X-Rays
  • In medical sciences X-rays are used in surgery for the detection of fracture, diseased organs, foreign matter like bullet, stones etc. They are used in treatment of cancer and in skin diseases.
  • In Engineering, X-rays are used in detecting faults, cracks, flaws and gas pockets in the finished metal products and in heavy metal sheets.
  • In Scientific Work, X-rays are used in studying crystal structure and complex molecules.
  • In Custom Department X-rays are used in custom department for detection of banned materials kept
Infrared Rays:
  • Discovered by Hershel.
  • Are used to muscular strain.
  • For taking photographs in fog or smoke.
  • In green house to keep plants warm.
  • In weather forecasting through infrared photography.
  • In night vision apparatus
Ultraviolet Rays:
  • Discovered by Ritter
  • Used in the study of molecular structure.
  • In sterilising the surgical instruments.
  • In the detection of forged documents and finger prints.
  • In the water purification system to kill harmful micro organism in water.
Devices Based on Electromagnetic Radiations:
  • Infrared radiation used in breath analyser.
  • Infrared photography is used to detect H1N1 virus infected people at the airport.
  • Microwave are used in the microwave own, microwave are not not absorbed by air, glass, paper and hence do not get warmup.
  • CT Scan  is medical device in which electromagnetic waves are used.
  • X rays are used in Magnetic Resonance Imaging(MRI)
  • A TV remote controller is a device in which infrared radiation are used.
  • In RADAR (Radio Detection and Ranging)  radio waves are used to locate , guide and identify object.
  • Semiconductor are insulator at room temperature but behaves as conductor as the temperature increases and this phenomenon are studied under the topic electronics.
  • For increasing the conductivity impurity are added.
  • Semiconductor are of two types i.e p-types  and n-types
p-n Junction Diode:
  • An arrangement  consisting a p-type and n-type semiconductor is called a p-n junction.
  • The device containing this p-n junction is called p-n junction diode.
Types of Diode:
LED stands of light emitting diode and it is used in electronic gadgets as indicator light.
Zener Diode:
  • It is used as voltage regulator.
  • It can not be damaged but reverse current works in that situation.
Terms related to Diode:
  • Depletion layer is a region between p-n junction where there is no charge carriers.
  • Potential Barrier is the potential difference across the depletion layer.
  • Forward Biasing is the arrangement in which p-side of the diode is connected to the positive terminal of the battery.
  • Reverse Biasing is the arrangement in which p-side of the diode is connected to the negative terminal.
  • It is a combination in which p-n junctions are joined in series.
  • Transistors are of two types n-p-n transistors and p-n-p transistors.

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