Download CAT –III QUESTION BANK ENGINEERING PHYSICS

CAT –III QUESTION BANK
ENGINEERING PHYSICS-1 (PH6151)
PART –A
1. Name methods by which ultrasonic waves are produced
Piezo-electric method and Magnetostriction method
2. What is meant by magnetostriction effect?
When a ferromagnetic material in the form of a bar (like iron or nickel ) is subjected to
alternating magnetic field, the bar expand and contracts in length alternately The frequency of
contraction or expansion is twice the frequency of alternating magnetic field. This effect is
known as Magnetostriction effect.
Frequencies ranging from a few hundred hertz to 300,000 hertz
3. What is meant by NDT?
It is a method of testing a material without destructing or damaging the materials
4. Mention the properties of ultrasonic waves
a. When an ultrasonic wave meets the surface of separation between two media, it
undergoes reflection.
b. By the superposition of two ultrasonic waves of nearly the same frequency beats
can be produced.
c. The frequency of ultrasonic waves varies when there is a relative motion between
the source and receiver. That is they exhibit the phenomenon of Doppler Effect
d. When an ultrasonic wave meets obstacles, the waves will bend round the edge of
the obstacle and thus they exhibit the phenomenon of diffraction
5. What is meant by SONAR? What are the application of SONAR
Sound Navigation and Ranging. The principle of SONAR is based on the echo technique
1) It is used to locate shoal of fish
2) It is used for seismic survey using an instrument called as seismography
3) It is useful in all merchant and military ships
4) It is used to find the depth of sea and distance and direction of submarines.
6. What is sonogram
Sonogram is an instruments used to visualize the images of the internal organs of the body by
using high frequency ultrasonic sound waves.
7. What is meant by LASER? Give its special characteristics.
Laser stands for Light Amplification by stimulated Emission of Radiation
High directionality, High intensity, highly monochromatic and Highly coherent
8. What is population inversion? What is the need for population inversion for producing
lasers?
The establishment of a situation in which the number of atoms in higher level is more that in
lower energy level is called population inversion.
Stimulated emission process is a key factor for the production of laser. For stimulated emission,
more number of atoms must be in the excited state.
9. Distinguish between spontaneous and stimulated emission of radiation
Spontaneous emission
Emission of light radiation is not triggered by
external source
Emitted photon travels in random direction
Emitted photon cannot be controlled
This process is a key factor for ordinary light
Stimulated emission
Induced emissions of light radiation caused by
incident photons
Emitted photon travels in particular direction
Emitted photon can be controlled
This process is a key factor for laser operation
10. Distinguish between homo junction and hetero junction laser.
Homojunction Laser
Hetrojunction Laser
It is made from single crystalline material
It is made from different crystalline materials
Power output is low
Power output is high
Pulsed output ( Sometimes continuous)
Continuous output
Cost is less
Cost is more
Life time is less
Life time is more
Example: GaAS, In P
Example: GaAS/GaAlAs and InP/ InAlP
11. What are the factors affecting the acoustic quality of a building?
Reverberation time, Presence of echoes, adequate loudness,Focusing and interference effects,
Resonance’s within the building, Echelon effect and noises
12. Define reverberation time of an auditorium
The interval of time taken by sustained or continuous sound to fall in intensity to one
millionth of its original value is called reverberation time.
13. Define absorption co-efficient of the material
Definition: The sound absorption coefficient (a) of a material is defined as the ratio of sound
energy absorbed by it to the total energy incident on it.
Sound energy absorbed by the surface
Absorption coefficient (a) = ------------------------------------------------------Total sound energy incident on the surface
14. Define intensity of sound and its unit
Intensity of sound is measured by the quantity of wave energy flowing across unit area held
normally to the direction of propagation of the sound waves per second.
Its unit is watt/m2.
Expression for the Intensity of Sound
Intensity of sound,
I  2 2 n2 a 2  v
n = frequency of the sound wave
a = amplitude of the wave
ρ = density of the medium through which sound travels
v = velocity of the sound in the medium.
15. State Weber – Fechner law.
Loudness of sound judged by the ear is proportional to logarithm of intensity.
Loudness L is directly proportional to log10 (I)
L prop log10 (I)
L = k log10 (I)
Here k is a constant depending on the sensitivity of the ear, quality of the sound and other
factors.
16. Explain the basic principle of fiber optic communication?
It is based on the principle of total internal reflection
17. What are the conditions to be satisfied for total internal reflection?
The core should have higher refractive index (n1) than that of the cladding (n2)
The light should incident at an angle greater than critical angle c
18. Distinguish between step-index and graded-index fibers
Step Index Fiber
Graded Index Fiber
Definition: Optical fiber with acore having
Definition: Optical fiber whosecore has a
uniform refractiveindex is called step index
refractive index thatdecreases with increasing
fiber.i.e., refractive index abruptlychanges in radialdistance is called Graded indexfiber.
a single step at corecladding interface
Attenuation is more
Attenuation is less.
Numerical aperture is more.
Numerical aperture is less.
Signal distortion is more
Signal distortion is less.
Bandwidth is small
Bandwidth is large.
19. Distinguish between single mode and multimode fiber?
S.No Single Mode Fibre
1
2
In single mode fibre only one mode (LP 01)
mode or HE11 mode) can propagate through
the fibre
The single mode fibre has smaller core
diameter (10 µm ) and the difference
between the refractive indices of core and
Multimode fibre
Multimode fibre allows a large number of
paths or modes for the light rays traveling
through it
Generally in multimode fibre the core
diameter and the relative refractive index
difference are large than the single mode
the cladding is very small.
In practice there is no dispersion ( i.e. no
degradation of signal during traveling
through the fibre)
Since the information transmission
capacity proportional to dispersion, the
single mode fibers are mode suitable for
long distance communication
fibre.
Even though there is self focusing effect
3
there is signal degradation due to multimode
dispersion and material dispersion
Due to large dispersion and attenuation of
4
the signal the multimode fibers are less
suitable for long distance communication.
Any how these fibers are generally used in
the local area network
Launching of light into single mode fibers Launching of light into fibre and jointing of
5.
and jointing of two fibers are very two fibers are easy in these fibers
difficulty
Fabrication is very difficult and so the fibre Fabrication is less difficulty and so the fibre
6..
is so costly
is not costly
Laser diode is used for launching light into Semiconductor laser is used.
7.
the fibre
Any four points
20. Define acceptance angle and numerical aperture
Numerical aperture
Acceptance angle
Light gatheringcapacity of an optical fiber is
The Maximum angle at (or) below which the
called Numerical aperture.
light can suffer total internal reflection is
called acceptance angle.
Sine of the acceptance angle is called numerical Acceptance angle
aperture. Formula to find the Numerical
  sin  12  22
aperture.
NA =

12   22



21.
Calculate the increase in the acoustic intensity level when the sound intensity is doubled.
Sound intensity ratio (I2/I1) =2
Sound intensity level  = 10 log10 (I2/I1)
22.
Given that the velocity of ultrasonic wave in sea water is equal to 1440 m/s. find the
depth of a submerged submarine. If an ultrasonic plus reflected from the submarine is
received 0.33 sec after sending out ultrasonic waves.
Total distance travelled by ultrasonics = v x t
Depth of submerged submarine (d) is half of the total distance travelled by ultrasonic.
23.
Calculate the wavelength of light emission from GaAs whose band gap is 1.44 eV.
 = (hc/ Eg) Å h – 6.625 x 10-34, c = 3 x 108 m/sec