Page 314 - General Knowledge

GENERAL KNOWLEDGE 2019

 The positive charge is uniformly distributed over the entire sphere and the electrons are
embedded in the sphere of positive charge. The total positive charge inside the atom is
equal to the total negative charge carried by the electrons, so that every atom is electrically
neutral.
 According to Thomson, if there is a single electron in the atom, the electron must be situated
at the centre of the positive sphere. For an atom with two electrons, the electrons should be
situated symmetrically with respect to the centre of the sphere i.e., opposite sides of the
centre at a distance of r /2, where r is the radius of the positive sphere.

Rutherford atom model
 Based on the results of - particle scattering experiment Rutherford suggested the following
picture of the atom.
 Atom may be regarded as a sphere of a diameter 10 -10 m, but the whole of the positive
charge and almost the entire mass of the atom is concentrated in a small central core called
-14
a nucleus having a diameter of about 10 m.
 As the atom is electrically neutral, the total positive charge of the nucleus is equal to the total
negative charge of the electrons in it.

Bohr atom model
 Rutherford atom model explains the stability of the atom and the emission of sharp spectral
lines.
 An electron cannot revolve round the nucleus in all possible orbits. The electrons can
revolve round the nucleus only in those allowed or permissible orbits for which the angular

momentum of the electron is an integral multiple of .

 These orbits are called stationary orbits or non-radiating orbits and an electron revolving in
these orbits does not radiate any energy.

Sommerfeld atom model
 According to Sommerfeld, the path of an electron around the nucleus, in general, is an
ellipse with the nucleus at one of its foci.
 The velocity of the electron moving in an elliptical orbit varies in different parts of the orbit.
This causes the relativistic variation in the mass of the moving electron. Now, when elliptical
orbits are permitted, one has to deal with two variable quantities.

 where a and b are semi-major and semi-minor axes respectively of the ellipse.

Laser
 The light emitted from an ordinary light source is incoherent, because the radiation emitted
from different atoms has no definite phase relationship with each other. For the interference
of light, coherent sources are essential.
 Two independent sources cannot act as coherent sources. For experimental purposes, from
a single source, two coherent sources are obtained. In recent years, some sources have
been developed, which are highly coherent known as LASER.

 The word ‗Laser‘ is an acronym for Light Amplification by Stimulated Emission of
Radiation.

310 | P a g e shop.ssbcrack.com