Atoms and Nuclei · Physics · Class 12

The energy of an electron in the ground state of hydrogen atom is -13.6 eV . The kinetic and potential energy of the electron in the first excited state will be

The potential energy between two nucleon's inside a nucleus is minimum at a distance of about

Assertion (A): An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of $180^{\circ}$.

Reason (R): The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus.

The ratio of the nuclear densities of two nuclei having mass numbers 64 and 125 is

The diagram shows four energy level of an electron in Bohr model of hydrogen atom. Identify the transition in which the emitted photon will have the highest energy.

The radius of the $$\mathrm{n}^{\text {th }}$$ orbit in Bohr model of hydrogen atom is proportional

A hydrogen atom makes a transition from $$n=5$$ to $$n=1$$ orbit. The wavelength of photon emitted is $$\lambda$$. The wavelength of photon emitted when it makes a transition from $$n=5$$ to $$n=2$$ orbit is

The curve of binding energy per nucleon as a function of atomic mass number has a sharp peak for helium nucleus. This implies that helium nucleus is

(a) Two energy levels of an electron in hydrogen atom are separated by 2.55 eV . Find the wavelength of radiation emitted when the electron makes transition from the higher energy level to the lower energy level.

(b) In which series of hydrogen spectrum this line shall fall?

The earth revolves around the sun in an orbit of radius $1.5 \times 10^{11} \mathrm{~m}$ with orbital speed $30 \mathrm{~km} / \mathrm{s}$. Find the quantum number that characterises its revolution using Bohr's model in this case (mass of earth $\left.=6.0 \times 10^{24} \mathrm{~kg}\right)$

Draw a graph showing the variation of potential energy of a pair of nucleons as a function of their separation. Indicate the region in which the nuclear force is (a) attractive and (b) repulsive.

(a) (i) Differentiate between 'distance of closest approach' and 'impact parameter'.

(ii) Determine the distance of closest approach when an alpha particle of kinetic energy 3.95 $$\mathrm{MeV}$$ approaches a nucleus of $$Z=79$$, stops and reverses its directions.

OR

(b) (i) State three postulates of Bohr's theory of hydrogen atom.

(ii) Find the angular momentum of an electron revolving in the second orbit in Bohr's hydrogen atom.

(a) What is meant by ionisation energy? Write its value for hydrogen atom.

OR

(b) Define the term, mass defect. How is it related to stability of the nucleus?

(a) (i) Distinguish between nuclear fission and fusion giving an example of each.

(ii) Explain the release of energy in nuclear fission and fusion on the basis of binding energy per nucleon curve.

OR

(b) (i) How is the size of a nucleus found experimentally? Write the relation between the radius and mass number of a nucleus.

(ii) Prove that the density of a nucleus is independent of its mass number.