Question

In the early 20th century, observations of physical phenomena were not matching up with classical theory. Some of these were the photoelectric effect, spectral lines, blackbody radiation, the discovery that an atom was divisible, the discovery of the electron and atomic nucleus.
a.) What did Planck, Einstein, and Bohr have to do to the classical theory in order to get it to match observations of these phenomena?
b.) What were some of the implications of this? (Refer to your answer to part a.)
c.) Explain what the photoelectric effect is in terms of Einstein

Answer 1

In the early 20th Century observation of spectroscopic data several theories have been proposed regarding the atomic structure. According to classical physics, an electron in an orbit around the nucleus should emit EM radiation or Photons continuously because it is accelerating continulosly in a curved path.It leads to loss of energy then , electron should fall in the nucleus.But it is not happening.

a) Plack introduced a quantum theory of Hypothesis, accoding to it radition emitted by the black body as a simple harmonic oscillators with small units of energy called qunata or photons.Following Plank's idea, Einstein explained Phto Electric effect in which conservation of Energy takes place by the photns when they incident on the metal surface. Bohr developed an atomic model as an electron can move along one of the discrete sets allowed orbits for which angular momentum of electron is equal to an integral multiple of .

b) Qunatum theory, Phtoelectric Effect and Atomic model with Hydrogen of atoms

c) Emission of electrons by the action of light is called the PhotoElectric effect. According to Eienstein 's explanation, in photoelectric effect one photon is completely absorbed by one electron, which thereby gains the quatum of energy and may be emitted from the metal.

Einstein's Phto Electric Equation can be written as

It is combination of threshold energy or workfunction and kinetic energy . And also intensity of emitted electrons is directly proportional to the intensity of incident radiation.

d) JJ.J.Thomson's proposed the plum pudding model . Rutheor ford observed alpha particle scattering. Drawbacks of Ruther ford model are the stability of the atom as whole and distribution of electrons outside the nucleus. Bohr proposed a quantum mechanical description of the atom to replace the early model of Rutherford. Bohr explained that, (i)no energy is radiated by the electron as long as it remains in its definite or stationary orbit, thus permitted orbits are non-radiating paths of electrons.(ii) the radiation of energy takes place only when an electron jumps from one permitted orbit of higher energy to another permitted orbit of lower energy. The difference of energies is radiated and must be a quantum of enrgy h .

e) From Bohrs theory of hydrogen atom of electron energy levels, when hydrogen atom is subjected to external energy , electron jumps from lower energy state to higher energy state i.e. Hydrogen atom is excited,and it is not stable after 10^-8 seconds it return to the ground state with radiating some energy of different wavelengths called spectral series .They are called sprectral series such as Lyman, Balmer, Paschen, Bracket and Pfund series.