ENGINEERING PHYSICS


ENGINEERING PHYSICS
B.TECH EXAMINATION
SEM III, 2012-13
UTTARAKHAND TECHNICAL UNIVERSITY(UTU)


Time: 3 hours
Total marks: 100
Unit -I
Attempt any four of the following:
  1. What do you understand by absolute motion; define inertial and non inertial frames? Explain the Newtonian principle of relativity.
  2. Discuss the non existence of aether using Michelson Morley experiment.
  3. An event occurs at x=100 m, y =10 m, z=5 m and t =100μ sec in frame S. Find the coordinates of this event in a frame S' which is moving with velocity 2.7 x 108 m/s w.r.t the frame S along the common XX' axis using 1) Galilean transformation 2) Lorentz transformation.
  4. State the fundamental postulate of the special theory of realtivity and write down Lorentz's direct and inverse transformation equations. Discuss how these accounts for the phenomenon of length contraction by explaining the concept of proper length.
  5. An iron furnace radiates 1.53 x 105 calories per hour through an opening of the cross section 10-4 sq meter. If the radiation emittance of the furnace is 0.80, calculate the temperature of the furnace. Given σ =1.36 x 10-8cal/m2-s-K4
  6. State Stefan's law of heat radiation. Describe an experiment to determine Stefan's law.
Unit -II
Attempt any two of the following:
  1. (a) Obtain the condition of the interference of the light reflected by a thin parallel film. Explain how you device a non reflecting film.
    (b) If the angle of the wedge is 0.25o and the wavelength of the sodium lines are 589 nm and 589.9 nm, find the distance from the apex at which the maxima due to two wavelengths first coincides when observed in reflected light.
  2. (a) In the second order spectrum of a plane diffraction grating, a certain spectral line appears at an angle of 10o, while other line of wavelength 0.05 nm greater appears at an angle 3" greater. Find the wavelength of the lines.
    (b) Explain the term coherence and write the method to produce coherent sources of light. Also write down the suitable method to find out the thickness of the thin filmby using the biprism.
  3. (a) A grating with 1500 ruling per inch is illuminated normally with white light from 400-700 nm. Show that only the first order spectrum is isolated but the second and third orders overlap.
    (b) Derive the formula for the wavelength of the light used and refractive index of a liquid in Newton's ring experiment.

Unit -III
Attempt any two of the following:
  1. (a) How can you produce plane, circularly and elliptically polarized light? Also explain how to distinguish between circularly polarized light and unpolarized light experimentally.
    (b) Explain the principle of LASER. Derive the relation between the Einstein's coefficients.
  2. (a) Draw the schematic diagram of the He-Ne laser. Using energy level diagram explain its working.
    (b) A plane polarized light of wavelength 600 nm is incident on a thin quartz plate cut with faces parallel to the optic axes. Calculate the ratio of the intensity of ordinary and extra-ordinary light makes an angle 30 with the optic axis. Refractive index of the ordinary and extra-ordinary rays = 1.633
  3. (a) A plane polarized light of wavelength 600 nm is incident on a thin quartz plate cut with faces parallel to the optic axes. Calculate
    (i) the minimum thickness of the plate which introduces a phase difference of 60o between ordinary and extra-ordinary rays.
    (ii) The minimum thickness of the plate for which ordinary and extra-ordinary rays will combine to produce plane polarized beam. Refractive index of the ordinary and extra-ordinary rays=1.633.
    (b) What are optically active substances? Explain the working of a polarimeter to find the specific rotation of cane sugar solution with suitable diagram.
Unit -IV
Attempt any two of the following:
  1. (a) A paramagnetic material has a magnetic field intensity of 104 Am-1. If the susceptibility of the material at room temperature is 3.7 x 10-3 . Calculate the magnetization and flux density of the material.
    (b) A system of electron spins is placed in a magnetic field of 2 Wb/m2 at a temperature T. The number of spins parallel to the magnetic field is twice as large as the number of antiparallel spins. Determine T.
  2. (a) A magnetic material has a magnetization of 2300 Am-1 and produces a flux density of 0.00314 Wb/m-2. Calculate the magnetizing force and the relative permeability of the material.
    (b) A positive point charge Q is at the center of a spherical conducting shell of an inner radius R1 and the counter radius Ro. Determine E and V as the function of the radial distance R.
  3. (a) Find the poynting vector on the surface of a long, straight conducting wire (of radius b and conductivity σ) that carries a direct current I. Verify the poynting's theorem.
    (b) State and prove Poynting's theorem and explain each term.
Unit -V
Attempt any two of the following:
  1. (a) Derive the London equation of superconductivity. Show that the second London equation explains Meissner effect.
    (b) Calculate the critical current density for 1 mm diameter wire of lead at
    (i) 4.2 K and (ii) 7 K.
    Given : Tc for lead is 7.18 K and Ho for lead is 6.5 x 104A/m.
  2. (a) The London penetration depths for Pb at 3K and 7.1 K are respectively 39.6 nm and 173 nm. Calculate its transition temperature as well as the depth 0K.
    (b) A nucleon is confined to a nucleus of diameter 5 x 10-4 m. Calculate the minimum uncertainty in the momentum of nucleon. Also calculate the minimum kinetic energy of the nucleon.
  3. (a) Derive the relation for energy levels of a particle confined within one dimensional rigid wall with infinitely high sides.
    (b) Calculate the uncertainty in the angle of emergence of 1 MeV electron passing through a hole of 20 micron.
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