SUB: PHYSICS                                                                                              Test: Homework

CLASS: ISC-II, PUC-II

PART-A

Question 1 [write the most appropriate answer]

(a) Bohr Radius is 53 pm? What would be the radius of Li+ ion in its ground state if it were to follow Bohr’s model?

A. 53 pm                       B. 27 pm

C. 18 pm                       D. 13 pm

(b) Two H-atoms collide inelastically, maximum amount by which their Kinetic Energy can reduce is?

A. infinite                                                      B. zero

C. depends on external environment       D. 10.20 eV

(c) Since Angular momentum is a vector in principle, it can point in infinite number of directions. But according to Bohr’s model this is not true. Why?

A. Conservation of angular momentum.

B. Conservation of energy.

C. Quantization of angular momentum

D. Conservative force field.

(d) A beam of free electrons are shot at free protons, why electrons and protons do not combine to produce a H-atom?

A. Conservation of angular momentum.

B. Conservation of energy.

C. Quantization of angular momentum

D. Conservative force field.

Question 2 [Short answer]

(d) Why mass of H-atom is less than sum of mass of protons and electrons in it.

(e) Why electronic transaction from higher to lower energy levels is always an electromagnetic form of energy?

(f) A positronium is like a H-atom where proton is replaced by the positron. A positron is the anti-particle of an electron, that is, it has the same charge as proton and same mass as electron? What would be ground state energy of positronium if ground state energy of H-atom is given by En = – mee4 / (8 e0 n2h2). me is the reduced mass of the H-atom = mass of electron. Reduced mass of positronium is me/2.

(g) If a proton had a radius R and the charge was uniformly distributed according to Bohr’s theory what would be the ground state energy of a H-atom if R=0.1 Angstrom, R= 10 Angstrom.

(h) In stable nuclei number of protons is more than that of neutrons, why?

PART-B

Question 3

Deuteron is a bound state of a neutron (n) and a proton (p) with a binding energy BE = 2.2 MeV. A g-ray of energy E is aimed at a deuteron nucleus to try to break it into a neutron and proton so that n and p move in direction of incident  g ray. If E = B.E. show that this is not possible. How much should BE be so that such a process can occur.

Question 4

Total charge –Q is uniformly distributed along length of a ring of radius R. A small test charge = q of mass m is kept at center of ring and is given a gentle push along the axis of the ring.

a) Show that the particle executes SHM.

b) What would be its time period?

Question 5

For a sphere of radius R with charge density given by r(r) = kr for r <= R, and = 0, find the electric field at all points r. Also find the potential.