STEC

1. Final Suggestions (All chapters)
Presenting By-
Dr. Hasina Akther
Assistant Professor
Physics

2. Questions on Elasticity
1. Definitions: Breaking stress, Factor of safety, Hooke’s Law, Different types
of modulus, Compressibility, Modulus of rigidity, Poission’s ratio, bending
momentum, Flexural rigidity, Cantilever.
2. State Hooke’s Law and draw stress-strain diagram, write details.
3. Shear is equivalent to compression and extension, prove that.
4. Prove that η = 1/2(α+β) where constants means its usual meaning.
5. Find out the co-relations among Y, K, η, σ, α and β [Y = 3K (1-2σ), 9/Y =
3/η +1/K, Y=2(1+σ), σ=3K-2/(6K+2)]
6. For bending the total moment of the forces, M = YIg/R.
7. What are transmission of heat & thermal conductivity and determine it by
the radial flow method of heat?

3. Math
1. A wire 8 m long and 1 mm in diameter, supports a mass of 8 kgm. It is stretched by 1 mm.
Calculate the Young’s modulus of the wire.
2. A pressure of 84 Kpa decreases the volume of 2004 L of water by 0.004 percent. Compute the
compressibility of water.
3 . Calculate the Poission’s ratio for a material given Y=12.25 N/m2 and =4.55×1010N/m2 .
4. Calculate  and σ for silver given Y and K for silver 7.25×1011 dynes/cm2 and 11×1011
dynes/cm2 .
5. A steel wire of 1.00 mm radius is bent in the form of a circular arc of radius 50 cm.
Calculate (I) the bending moment (ii) the maximum stress.[ Y=2×1012 dynes/cm2].
6. A Cantilever of length 50 cm is depressed by 15.0 mm at the loaded end. Calculate the
depression at a distance of 30 cm from the fixed end.
7. The opposite faces of a metal plate of 0.2 cm thickness are at a difference of temperature
of 100C and the area of the plate is 200 sq. cm. Find the quantity of heat that will flow
through the plate in one minute if K=0.2 CGS units.
8. An ice box is built of wood 1.75 cm thick, lined inside with cork 3 cm thick. If the
temperature of the inner surface of the cork is 0C and that of the outer surface of the
wood is 12 0C, what is the temperature of the interface? [ the thermal conductivity of
wood are 0.0006 and cork 0.00012 CGS unit.

4. Questions on Viscosity
1. Definitions: Viscosity, Laminar or viscous fluid, velocity
gradient, critical velocity, kinematic viscosity.
3. Define co-efficient of viscosity (Newton’s law of viscous
flow).
4. Write four assumptions for Poiseuille’s method of measuring
the viscosity.
5. Describe Poiseuille’s method for determining the coefficient of
viscosity of a liquid.
6. Discuss the necessary correction that must be applied to the
theoretical expression on which the method is based.

5. Questions on Quantum Physics
1. Brief the quantum theory of radiation.
2.What is wave function? Write the physical significance
of wave function.
3. What is Compton effect and find the relation
'− = (1−cos).
4. Write short note about black body radiation, electron
microscopy and Scanning electron microscope.
5. Give the differences between classical and quantum
mechanics.

6. Questions on Surface Tension
1. Definitions: Surface tension, surface energy, cohesive force,
adhesive force, molecular range, sphere of influence,
capillarity, angle of contact.
2. Define surface energy. Show that the surface energy per unit
area is numerically equal to the surface tension per unit length
3. Distinguish between cohesion and adhesion motion.
4. Find an expression for the excess pressure across the curved
surface of a curved membrane.
5. Find an expression for the height to which a liquid may rise in
a capillary tube.

7. Questions on Dynamics of circular motion
1. Definitions: Axis of rotation, torque, moment of inertia, angular
acceleration, Radius Of Gyration.
2. What is moment of inertia? Write the relation among torque, moment of
inertia and angular acceleration.
3. State and prove the theorem of parallel axis in moment of inertia.
4. Show that the moment of inertia of a uniform circular disc about an axis
passing through its centre and perpendicular to its plane is 0.5 MR2.
3. The moment of inertia of an annular disc. Or Prove I=M(R2
2-R1
2)/2.
4. The moment of inertia of a spherical shell & a solid sphere.
5. The moment of inertia of a Flywheel.

8. Questions
Math
1. A plate of metal 10-2 m2 area rests on a layer of castor oil 2x103 m thick whose coefficient of
viscosity is 1055 N-s/m2. Calculate the horizontal force required to move the plate with a
uniform speed of 3x10-2 m/sec.
2. Calculate the mass of water flowing in 10 seconds through a horizontal capillary tube of
circular cross-section of radius 10-3 m. The tube is fitted at the bottom of a constant level tank
at a depth of 1 m. Length of the tube is 0.3142m, coefficient of viscosity of water=10-3N-
s/m2, density of water = 103 kg/m3.
3. Calculate the excess pressure inside a soap bubble of radius 3×10-3 m. Surface tension of soap
solution is 20 ×10-3 N/m. Calculate also the surface energy of the soap-bobble.
4. What is the work done in blowing a soap bubble of radius 10 cm? What additional work will be
performed in further blowing it, so that its radius becomes 15 cm? T=30 dynes/cm.
5. In a capillary tube water rises to a height of 0.1 m. in the same capillary tube mercury is
depressed by 3.42×10-2m. Angle of contact for water and mercury are 0 and 135.Calculate
the surface tension of mercury[ T for water is 72×10-3N/m and density of Hg is
13.6×103kg/m3.
6. A liquid of density 1.05 gm/cc and angle of contact 20 has a vertical capillary tube of 2 mm
diameter dipping into it. If the surface tension of the liquid be 235dynes/cm, find the rise of
the liquid in the capillary tube.

9. Optics
1. Define wave front. Write the Huygens’ principle.
2. What are the differences between interference and diffraction?
3. How will you determine the wavelength of light using Fresnel’s
biprism?
4. Write the conditions for constructive & destructive interference.
5. Define the radius of curvature of Newton’s ring.
6. Diffraction grating and its uses.
7. Difference between zone plate & convex lens.
8. Discuss the Fraunhofer diffraction at a single slit. Draw the intensity
distribution for the diffraction pattern.
9. Explain the terms “plane of polarization, plane of vibration and
Brewster’s law”.
10. Describe the construction of a nicol prism and show how it can be used
as a polarizer or an analyzer.

10. Optics Maths
• A biprism is placed 5 cm from a slit illuminated by sodium
light (5890A). The width of the fringes obtained on a screen
75 cm from the biprism is 9.424X 10-2 cm. What is the
distance between the two coherent sources?
2. In a Newton’s rings experiment the diameter of the 15th ring
was found to be 0.590 cm and that of the 5th ring was 0.336
cm. If the radius of the plano-convex lens is 100 cm,
calculate the wave-length of light used.
3.How many orders will be visible if the wavelength of incident
radiation be 5000 A.U. and the number of lines on the
grating be 14000 an inch?

11. Sound & Crystal Physics
1. i) Introduction to Ultrasonics,ii) Ultrasonics production- Piezo
electric method.
2. Write about the properties of Ultrasonic waves.
3. Show that, the inter-planar distance of orthorhombic crystal
is given by
Math
1. Show that, in a simple cubic lattice the separation between the
successive lattice planes (100), (110) and (111) are in the ratio 10.71
0.58.
2. The lattice constant of a simple lattice is ‘a’. Find the lattice spacing’s
between (111), (112), and (113) lattice planes.
2
2
2
2
2
2
1
c
l
b
k
a
h
d
++
=