PGTRB (PHYSICS) – ATOMIC PHYSICS

ATOMIC PHYSICS

• At normal
  pressure gases do not conduct electricity (poor conductors of electricity).

• The
  conduction of electricity in a gas will vary with pressure. The behavior is
  studied with the help of a discharge tube.

• When the
  pressure in the discharge tube is about 0.1mm of mercury cathode rays are
  produced.

• Cathode
  Rays:

• Cathode rays
  are fat moving electrons.

• Cathode rays
  are emitted normally from the cathode surface. Their direction is independent of
  the position of the anode.

• Cathode
  rays travel in straight line.

• Cathode
  rays possess momentum and kinetic energy. 

• Cathode
  rays produce heat when they strike a material surface.

• Cathode
  rays produce fluorescence when they strike a number of crystals, minerals and
  salts.

• Cathode
  rays strike a metal, X-rays are emitted.

• Cathode
  rays affect the gases through which they pass.

• Cathode
  rays affect the photographic plates.

• Cathode
  rays are deflected from their straight line path by both electric and magnetic
  field. The direction of deflection shows that they are negatively charged
  particle.

• Cathode
  rays travel with high velocities.

• Cathode
  rays are found to be electrons which are fundamental constituents of all atoms.

• Canal rays
  (Positive rays):

• Canel rays
  are positive ions. They move in opposite direction to that of cathode rays in
  the same discharge tube

• The mass of
  each ion is nearly equal to the mass of the gas atom.

• They are
  deflected by electric and magnetic fields. Their deflection is opposite to that
  of cathode rays.

• They travel
  in straight line.

• The
  velocity of canel rays are less than that of cathode rays.

• They affect
  photographic plate.

• They can
  penetrate through paper and thin foils of aluminums.

• They cause
  fluorescence.

• They ionize
  the gas through which they pass.

• J.J.Thomson:

• In 1887
  J.J.Thomson measured the specific charge –e/m (charge per unit mass) of the
  cathode ray particle.

• The value
  of e/m was independent of the gas used and also independent of the electrodes.

• A fine beam
  of cathode rays to the combined action of crossed electric and magnetic field
  e/m can be calculated.

• Uniform
  magnetic field is produced perpendicular to the plane of the paper an outwards
  through out the region between P1P2

• According
  to Millikan only very high viscous liquids like glycerin are used so that the
  oil drops acquire terminal velocity.

• X-rays are
  produced when fast moving electrons strike a metal target of high atomic
  weight.

• X-rays are
  produced in a Coolidge tube.

• X-rays are
  invisible.

• X-rays are
  allowed pass through gases.

• X-rays can
  be diffracted by crystals.

• There are
  two types of X-ray spectra:

• (i)                 
  Continuous
  spectra and

• (ii)               
  Characteristic
  spectra

• When the
  path difference (2dsinƟ) is an internal
  multiple of wavelength (nλ), there will be a constructive interference, which
  is known as Bragg’s law (2dsinƟ=nλ).

• Particle nature and
  wave nature of matter are called dual nature of matter.

• When light is focused on
  certain material electrons are ejected from the surface. This  is 
  known as Photo electric effect.

• The photo electric
  effect can be explained on the basis of quantum theory of radiation.

• Photons behave like
  particles. They possess energy and momentum only. They travel with the velocity
  of light.

• The photo electric
  effect starts only for a minimum frequency of light known as threshold
  frequency.

• According
  to De Broglie moving particles like electrons under certain conditions behave
  like a wave.

• Electron
  microscope is based on matter waves.

• Prout
  suggested that all elements are made up of hydrogen atoms.

• J.J.Thomson
  proposed that the atom is made up of a number of electrons embedded in a sphere
  of positive charge.

• Rutherford
  suggested that the electrons are revolving around the nucleus in circular
  orbits.

• According
  to Bohr the electrons revolving around the nucleus are fixed to specific orbits
  from which they do not radiate.

• If non-
  radiating orbits the angular momentum possessed by a electron is equal to Bohr atom model
  is successful in explaining the spectral lines of hydrogen and hydrogen like
  atoms.