NCERT Solutions for Chapter: Structure of Atom, Exercise 1: Long Answer Type

What is photoelectric effect? State the result of photoelectric effect experiment that could not be explained on the basis of laws of classical physics. Explain this effect on the basis of quantum theory of electromagnetic radiations.

Threshold frequency, ${\nu }_0$ is the minimum frequency which a photon must possess to eject an electron from a metal. It is different for different metals. When a photon of frequency $1.0\times {10}^{15} {\mathrm{s}}^{–1}$ was allowed to hit a metal surface, an electron having $1.988\times {10}^{–19} \mathrm{J}$ of kinetic energy was emitted. Calculate the threshold frequency of this metal. Show that an electron will not be emitted if a photon with a wavelength equal to $600 \mathrm{nm}$ hits the metal surface.

When an electric discharge is passed through hydrogen gas, the hydrogen molecules dissociate to produce excited hydrogen atoms. These excited atoms emit electromagnetic radiation of discrete frequencies which can be given by the general formula.

$\overline{\mathrm{\nu }}=109677 \left(\frac{1}{{\mathrm{n}}_{\mathrm{i}}^2}-\frac{1}{{\mathrm{n}}_{\mathrm{f}}^2}\right)$

What points of Bohr’s model of an atom can be used to arrive at this formula? Based on these points derive the above formula giving description of each step and each term.

Calculate the energy and frequency of the radiation emitted when an electron jumps from $\mathrm{n}=3$ to $\mathrm{n}=2$ in a hydrogen atom.

Why was a change in the Bohr Model of atom required? Due to which important development (s), concept of movement of an electron in an orbit was replaced by, the concept of probability of finding electron in an orbital? What is the name given to the changed model of atom?