APPLIED PHYSICS IN ENGINEERING

APPLIED PHYSICS IN ENGINEERING 

Time: 2 hours                                                                         Max. Marks: 50

Note: All the objective questions are compulsory (Part A)

Answer any ONE full question from each module (Part B)

Answer any ONE full question from two questions (Part C)

Physical constants: Velocity of light, c = 3×10⁸ m/s; h = 6.63×10^-34Js; k = 1.38×10^-23J/K;

m_e = 9.1×10^-31Kg; e = 1.6×10^-19C.

 

PART A

1.  The susceptibility of ferromagnetic material is

A) Positive and large                                        B) Negative and large 

C) Negative and small                                      D) Positive and small

2. The permeability of free space is equal to

A) Infinite        B) Zero                        C) 4π×10^-7 Henry/meter           D) 2π×10^-7 Henry/meter

3. Important characteristic of laser beam is

A) Interference    B) Diffraction          C) Dispersion      D) Coherence 

4. The required condition to achieve laser action in a system is

A) state of population inversion          B) existence of metastable state

C) a resonant cavity                             D) all the three

5. The idea of holography was first developed by

A) Dennis Gabor         B) Young         C) Ali Javan     D) Kamerlingh Onnes

6. Which one of the following is an attenuation mechanism?

A) Absorption                                                  B) Scattering

C) Microscopic and macroscopic bending                   D) All of these

7. Loss of power during transmission through optical fiber is called

A) Power factorB) Energy loss

C) Attenuation  D) Amplification

8.The basic principle of optical fiber is
A) Refraction                           B) Absorption

C) Total internal reflection                                D) Rayleigh scattering

9. Supply of energy to atoms for excitation is called

A) Glowing      B) Bombarding            C) Incidenting  D) pumping.

10. Two opposite poles (north pole and south pole) separated by a distance ‘2l’ constitute a

A) Magnetic dipole      B) Magnetic moment   C) Susceptibility          D) Superconductor

 

                                                                                                         (10 x 1= 10 MARKS)

 

 

PART B

MODULE 1

11.(a) Define superconductivity and explain Type I and Type II superconductors.(6 MARKS)

     (b) Calculate the probability of an electron occupying an energy level 0.02 eV above the Fermi level at 200 K.(4 MARKS)

OR

12.(a)Write a note on classification of magnetic materials.                                    (6 MARKS)

  (b)A magnetic material has a magnetization of 3300 A/m and produces a flux density of 0.00471 wb/m². Calculate magnetizing force and relative permeability of the material.(4 MARKS)

 

MODULE 2

13. (a) With help of energy level diagram, describe the construction and working of He-Ne laser.

(6 MARKS)

(b) The average output power of laser source emitting a laser beam of wavelength 6328 Å is 5mW. Find the number of photons emitted per second by the laser source.                                     (4 MARKS)

OR

14.(a) Explain briefly induced absorption, spontaneous emission and stimulated emission.

(6 MARKS)

      (b) Write any 4 differences between LED and LCD display.                      (4 MARKS)

 

MODULE 3

15.(a) Explain point to point communication using optical fiber with the help of a block diagram.

(6 MARKS)

    (b) An optical fiber 600m long has input power of 120mW which emerges out with power of 90mW. Find the attenuation in the fiber.                                                           (4 MARKS)

OR

16.(a) Explain the different types of optical fibers based on modes, refractive index and material.

(6 MARKS)

     (b) Calculate the V-number for a fiber of core diameter 40μm & with refractive indices of 1.55 and 1.50 respectively for core and cladding when the wavelength of the propagating wave is 1400 nm. Also calculate the number of modes that the fiber can support for propagation. Assume that the fiber is in air.

(4 MARKS)

 

PART C

17.(a) Derive the expression for numerical aperture and acceptance angle of an optical fiber. (6 MARKS)

(b) Explain briefly Meissner effect and Isotope effect.                                   (4 MARKS)

OR

18. (a) Describe the recording and reconstruction processes in holography, with the help of suitable diagrams.                                                                                                 (6 MARKS)

(b) Distinguish between soft and hard magnetic materials.                            (4 MARKS)

 

 

 

 

SCHEME OF EVALUATION

PART A

1. A) Positive and large

2. C) 4π×10^-7 Henry/meter

3. D) Coherence 

4. D) all the three

5. A) Dennis Gabor

6. D) All of these

7. C) Attenuation

8. C) Total internal reflection

9. D) pumping

10. A) Magnetic dipole

PART B

MODULE 1

11. (a) Superconductivity – definition (2 marks)

          Type I superconductors – explanation with graph (2 marks)

          Type II superconductors – explanation with graph (2 marks)

       (b) f(E) =    --------(1 mark)

           Substitution (2 marks)

           f(E)= 0.238   (1 mark)

OR

12.(a) Paramagnetic (2 marks), diamagnetic (2 marks), ferromagnetic (2 marks)

 

(b) B = µ₀(H+M)

H =  –M

 

Substitution and result = 450 A/m--------(1 mark)

µ_r = 1+χ

 = 1 +

Substitution and Result= 8.33------------(1 mark)

 

MODULE 2

13.(a) He- Ne laser diagram (1 mark)

          Energy level diagram (2 mark)

Construction(2 mark)

          Working principle (2 mark)

 

(b) n =   -------(1 mark)

 

           Substitution (2 marks)

            n = 1.59 ×10¹⁶ ---------(1 mark)

 

OR

14.(a) induced absorption (2 marks)

 spontaneous emission (2 marks)

 stimulated emission (2 marks)

 

(b) 4 differences between LED and LCD display (4 marks)

 

MODULE 3

15.(a) block diagram (2 marks)

          Components of Optical transmitter – explanation (2 marks)

          Components of Optical receiver – explanation (2 marks)

 

      (b) α =  log  dB/km--------(1 mark)

           Substitution (2 marks)

       Result = 2.08 dB/km----------(1 mark)

OR

16.(a) Based on modes- single mode and multimode fiber (2 marks)

          Based on refractive index- step index and graded index fiber (2 marks)

          Based on material- glass fiber, plastic fiber and PCS fiber (2 marks)

 

     (b) V = --------(1 mark)

Substitution and result= 35------(2 marks)

n =   -------------(1 mark)

Substitution andresult = 612------(1 mark)

 

PART C

17.(a)   sinθ=

µ =  = ------------------- (1 mark)
∴sinϕ_c  =
For total internal reflection to take place,
ϕ ≥ ϕ_c
or, sinϕ ≥ sinϕ_c
or,  sinϕ ≥ ---------------------- (1 mark)
But from figure, sinϕ =cosθ
∴cosθ ≥
i.e, (1-sin²θ)^1/2 ≥
sin²θ ≤ 1- (²-------------- (1 mark)

sin²θ ≤

From Equation (1), sin²θ=

∴ Condition for total internal reflection is.

  ≤

sin²i ≤

sin i ≤ ----------------- (1 mark)

i ≤ sin^-1

Thus, if the angle of incidence is greater than sin^-1 , total internal reflection and transmission of light will not take place.

i_m=  sin^-1--------------- (1 mark)

This angle is called acceptance angle for the fiber.

Numerical aperture NA=sin i_m= --------------(1 mark)

 

(b) Meissner effect (2 marks)

     Isotope effect (2 marks)

 

OR

18.(a) Recording of hologram – diagram (1 mark), explanation (2 marks)

          Reconstruction of holography – diagram (1 mark), explanation (2 marks)

     (b) soft and hard magnetic materials (any 4 differences) (4 x 1 = 4 marks)