# Ncert 12th Physics Chapter-12

## Limitations of Bohr’s Model

1. This model is applicable only to a simple atom like Hydrogen having Z= 1. The theory fails if Z>1. 2. It does not explain the fine structure of spectral lines in hydrogen atom. 3. This model does not explain why orbits of electrons are taken as a circular, whereas elliptical orbits are also possible. […]

## Hydrogen Spectrum or The Line Spectra of the Hydrogen Atom

# When we pass white light through a Prism it is disperse into seven colours. # But when we heat atomic gas(hydrogen) with the help of electric current and passed through a Prism then see what happened. After dispersion only some particular wavelength are seen on the screen. This is called line spectrum or discrete

## Energy of Electron in Stationary Orbits

As we know that the centripetal force is provided by the electrostatic force of attraction. The potential energy of the electron in an orbit of radius r due to the electrostatic attraction by the nucleus is The negative energy of electrons shows that the electron is bound to the nucleus and is not free to

## Bohr’s Theory of Hydrogen Like Atom

According to Bohr’s theory, A hydrogen atom consists of a nucleus with a positive charge Ze and a single electron of charge e⁻, which revolves around it in a circular orbit of radius r. Here Z is the atomic number and for hydrogen Z= 1. The electrostatic force of attraction between the nucleus and the

## Bohr’s Model of Hydrogen Atom

Bohr combined classical and early quantum concepts and give his theory in the form of three postulates. (I) Bohr’s first postulate was that an electron in an atom could revolve in certain stable orbits without the emission of Radiant energy. According to this postulate, each atom has certain definite stable state in which it can exist

## Drawbacks of Rutherford’s Model

Rutherford’s model suffers to major drawbacks. 1. Stability of Atom: According to Maxwell, an accelerated charged particles emits radiation(energy). In Rutherford Model of atom, electrons are moving in circular orbits, Thus having centripetal acceleration. So electrons should emits radiation and ultimate lose energy and pulled into nucleus and atom would not be stable. So Rutherford

## Distance of Closest Approach, Impact Parameter and Electron Orbits

Distance of Closest Approach: As the Distance particle approaches the nucleus, the electrostatic force of repulsion due to nucleus increases and the kinetic energy of α particle goes on converting into the electrostatic potential energy. At a certain distance r₀ from the nucleus, whole of the kinetic energy of α particle convert into electrostatic potential energy

## α-Particle Scattering Experiment by Rutherford

In this experiment H Geiger and E Marsden( Student of Rutherford and on suggestion of Rutherford) took ₈₃Bi²¹⁴ (Bismuth) as a source of α particles. A collimated beam of α particles of energy range (5 MeV to 7.7 MeV) was allowed to fall on 10⁻⁸ m to 10⁻⁶ m thick gold foil. The α particles

## Atoms

All elements consists of a very small invisible particles are called atoms. Atoms of some elements are same and atoms of different elements are different. #The first model of atom was proposed by JJ Thomson in 1898 called plum pudding model. According to this model, the positive charge of the atom is uniformly distributed throughout

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