# Back Engineering Physics July-2011

Unit -1

1.  A) i) Write down schrodinger’s equation for a particle of mass ‘m’ trapped in a 3-Dimensional Box of side ‘a’. Solve it for energy eigen values and eigen functions.

ii)   Find the lowest energy of a Neutron confined to a nucleus of size 10′14 meter.

iii) Write a short note on Quantum Mechanical Tunneling.

B) i) Define the fermi energy. Write down the expression for the Fermi-Dirac distribution law. also derive an expression for the Fermi Energy for the system of particles.

ii)   Calculate the Fermi Energy and Fermi velocity for free electron gas in Silver. Given the number of free electrons per unit volume in silver is 5.8^102S per meter cube.

iii) Write a short note on sommer fields free electron gas model.(8+4+4=16)

A) i) Explain the essential requirements for producing laser action. With neat and clean Diagram, Explain the working ofHe-Ne laser. How is population inversion achieved in this type of laser.

Unit-II

2.  Write short notes on the following :

a) Q-Switching.

b) Mode-locking.

OR

B) i) Give two fundamental differences between a hologram and a photograph.

Describe the method of recording the Hologram and reconstruction of image from it.

ir) Write short notes on the following :

a) Holographic Microscopy.

b) Semiconductor laser.

Unit-III

3.  A) i) What do you mean by Numerical Aperture of an Optical fibre. Find the

Expression for the Numerical aperture of a step index fibre.

ii)   Compare the maximum angle of acceptance and Numerical aperture of two fibres. Characterized by core and cladding index n, & n2 respectively

a) n! = L6, «, = 1.5

b) n1 = 2J, n2 = 1.5

OR

R) i) What do you mean by spatial and Temporal coherence, for propagating waves? Show that visibility is a measure of degree of coherence, s) Explain the use of optica! fibres in

a) Fibroscope

b) Sensor

c) Optical gyroscope

Unit-IV

4. A) i) Explain the construction and working of a GM. counter, give its important applications. How quenching is achieved in this counter.

ii) What are the advantages of proportional counter over GM. counter

OR

B) i) What is dielectric, dielectric constant and dielectric polarization. How shall you experimentally measure dielectric constant by schering method.

ii)   The capacity of a capacitor is increases by 120% when filled completely by dielectric find its dielectric constant

Unit-V

5. A)  i) State Ampere’s law in Integral and differential form. Why it is modified by Maxwells.

OR

B)  i) What do you mean by divergence of a vector field? Explain its physical significance.

ii)   Deduce Maxwell’s equations for free space and prove that the electromagnetic waves are Transverse.

iii)  If A=xz zi -2y3 z2 j+xy2 zk, find the values of