CENTRAL INSTITUTE OF PLASTICS ENGINEERING & TECHNOLOGY
Question Bank
3 MARK --- QUESTION
4/5 MARK ----QUESTION
COURSE: DPMT
SEMESTER: I
SUBJECT: ENGINEERING PHYSICS
2 mark - questions
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1 Define Stress
Ans. The restoring force per unit area is called stress
The unit of stress N/m2
Stress=F/A
2. Define Strain
Ans. The ratio of change in dimension to its original dimension
is called strain.
3. State Hooke’s Law and express in mathematical form
Ans. According to Hooke’s
law, within elastic
limits stress is proportional to strain, i.e.,
Stress a Strain
=Stress/Strain=Constant =E
The constant
of proportionality E is known as modulus of elasticity.
F=-kx, where k is the spring
constant. The negative
sign represents that the displacement is in the direction
opposite to the direction of applied force.
4. Define surface
tension or coefficient of surface tension
Ans. It is defined
as the work done per unit area in
increasing the surface
area of a liquid
under isothermal condition.
Unit N/m
5. State Boyle’s law
Ans. The law
states that at constant temperature, the volume of a given mass of a gas is inversely proportional to its pressure.
vᾃ 1/p
P1V1=P2V2=constant
6. State Charle’s law
Ans. The law states that pressure
remaining constant, the volume of a given mass of a gas is directly
proportional to its absolute temperature.
vαt
7. Define specific heat
Ans. Specific heat is defined as heat required
to raise the temperature of 1 kg of the material
by 1 Kelvin. Its unit is kilo calorie/kg
K or Joule/kg K having dimensional formula
as[ M0L2T-2ϴ-1].
8. Define specific heat at constant
volume Cv
Ans. The specific heat at
constant volume is the amount
of heat required
to raise the temperature
of one gram gas through 1⁰ C when the
volume of the gas is kept constant.
9. Define specific
heat at constant pressure Cp
Ans. The specific heat at constant pressure is the amount of heat required to raise the temperature of one gram gas through 1⁰ C when the pressure
of gas is kept constant.
10. Write Mayer’s
Relation
Ans. If Cp
and Cv are molar specific heats of an ideal gas at constant pressure
and constant volume respectively then Mayer’s
relation is stated as
Cp - Cv = R
Where R is universal gas constant having
value R= 8.3 Joulse mol-1K-1
11. What is Conduction?
Ans. It is the mode of transmission of heat in which
heat is transfrred from a region
of higher temperature to a region of lower temperature
without the bodily movement of the
molecules of a substance.
12. What is
Convection?
Ans. It is the
process in which particles near the source of heat absorbs energy, become
lighter and rises upwards. Liquids
and gases are heated by convection.
13. What is Radiation?
Ans. It is the
mode of transfer of heat
in which heat is transferred from source to the object
without any intervening medium taking
part.
14. State Newton’s
law of cooling
Ans. The law states
that the rate of loss of heat radiated
by the body is directly
proportional to the temperature difference between body and surroundings so long as the difference is small
mc
dΦ/dt ᾃ(Φ1 ------Φ2)
15. State the different types
of unit systems.
Ans.
(i)
CGS
System
(ii)
FPS
System
(iii)
MKS
System
16. Define dimensionless variables
Ans. Quantities which are variables but not having
dimension are called
dimensionless variables. e.g specific gravity,
strain
17. Define dimensional variables
Ans. Variable quantities which
have some dimension are called dimensional variables, e.g force,
momentum, acceleration etc.
18. Define dimensionless constants
Ans. The constant quantities which have no dimensions are called dimensionless constants, e.g. pure
numbers or some constants
19. Define dimensional constants
Ans. Some constants like velocity of light,
gravitational constant have got a fixed value and also have dimensions. These constants are called dimensional constants.
20. What is dimensional formula?
Ans. A dimensional formula
is an expression which shows how and which of the fundamental quantities enter into the units of
physical quantity.
21. Deduce the dimensional formula for (A)
Pressure (B) Work
Ans.
Therefore, the dimension formula of work is [ML2 T-2]
22. If
the value of acceleration due to gravity (g) =9.8 m/s2, what
will be its value in CGS system.
Ans.
23. State conservation of momentum
Ans. The law states
that if no external force acts on a closed
system of objects, the momentum of the
closed system remains constant, i.e when two or more bodies act upon one
another, their total momentum remains constant, provided no forces
acting on it.
24
What are the types of stress?
Ans.
a) Compression stress
b) Tensile stress
c) Shear stress
d) Hydrostatic stress
25. Define Young’s modulus and give its unit.
Ans. It is defined
as the ratio of the longitudinal stress
to the longitudinal strain in the range of
elastic limit.
Young’s modulus is denoted
by Y
i.e
Young’s Modulus (Y)= longitudinal stress / longitudinal strain
The unit of Young’s
modulus is N/m2.
26. Define Bulk Modulus and give its unit.
Ans. The ratio of normal stress to the volume strain is called as bulk modulus
of elasticity and it is denoted
by K.
Bulk Modulus(K)= normal stress/ volume strain
The unit of bulk modulus is N/m2.
27. Define Rigidity Modulus
and give its unit
Ans. The ratio of tangential
force per unit area to the angular
deformation produced is called modulus
of rigidity or rigidity modulus.
It is denoted by η.
F/A
η= tangential/shear strain=T/Φ=l/L
The unit of
rigidity modulus is N/m2.
28. Define Poisson’s Ratio
Ans. It is
defined as the ratio of lateral strain to the longitudinal strain of a body in
the elastic limit. It is denoted by σ.
σ=β/ᾃ
Where α is the longitudinal strain and β is the lateral strain.
29. Define Surface energy and write the relation between
surface tension and surface energy
Ans. Surface energy
is defined as the excess energy
at the surface of a material
compared to the bulk.
Work done W= F x ΔX
·
W=
T x 2l x ΔX
·
W= T x ΔA T=W/ ΔA
Where T is the surface
tension and W is the surface energy.
30. Define coefficient of viscosity and give its expression
Ans. The coefficient of viscosity is defined as the tangential force per unit area which resists the flow of two parallel
liquid layers having unit velocity gradient perpendicular to the streamline flow.
Where η is the coefficient of viscosity.
31. Define streamline and turbulent flow.
Ans. Streamline flow is a flow in
which all the particles of the fluid follow
a smooth path and these path do not cross one
over the other.
This flow is also
known as laminar flow.
Turbulent flow is a flow in which all the particles of the fluid do not follow a smooth path and these paths cross one over the other.
32. Define Reynold’s Number
Ans. It can be
defined for a number of different situations where a fluid is
in relative motion to a surface.
Where Re is the Reynold’s
number, η is the coefficient of viscosity, ρ is
the density of fluid and r is the radius of the tube and Vc is
the critical velocity. Re of less than 2100 are generally considered to be of laminar
type.
33. Define scalar and vector
with example
Ans. A scalar quantity
is defined as a
quantity that has magnitude only. Example speed, mass, volume.
A vector quantity is defined as a quantity that has both magnitude and
direction. Example velocity, acceleration, Force.
34. Define Centripetal force and give its expression
Ans. It is defined
as a component of force acting on a body in curvilinear motion
that is directed toward
the centre of curvature or axis
of rotation.
Where m is mass v is velocity and r is the radius.
35. Define Centrifugal force and give
its expression
Ans. It is defined as a tendency
of an object following a curved path to fly away from the centre of curvature.
Where w is the
weight of the object, v is the velocity, g the acceleration due to gravity and r radius of circle.
36. Write the relation between
linear acceleration and angular
acceleration
Ans.
37
Define angular momentum
and its unit.
Ans. The angular momentum (L) of a particle about a given origin is defined as,
L=rxp
Where r is the position vector of the particle
relative to the origin, P is the linear momentum of the particle. The SI unit of angular
momemtum is Nms or kg m2s-1.
38.
Define critical angle and
total internal reflection.
Ans. Critical angle is defined
as an angle of incidence at which the angle of refraction is 90 0.
Total internal reflection is the phenomenon
that occurs if the angle of incidence
is greater than a certain
limiting angle, called the critical
angle.
40
Write the characteristics of Laser
Ans.
·
Coherence
·
High intensity
·
High directionality
·
High monochromaticity
41. What is population inversion
Ans. It is the
state of achieving more number of atoms in the
higher energy state than in the
lower energy state,
N2> N1
42. What is pumping and write
different types of pumping
Ans. Pumping is
the mechanism of exciting the atoms from ground state to a higher energy state
by supplying energy from an external
source.
The commonly
used pumping methods are
·
Optical pumping
·
Electrical pumping
·
Direct pumping
41. What is optical pumping.
Ans. When the atoms are irradiated with an electromagnetic radiation of energy (hv), atoms in the
lower energy state absorb this
energy and are excited to the higher energy state. This method of pumping is called optical pumping.
This type of pumping technique is used in solid-state laser.
44. State the types of laser give example
Ans.
·
Solid state laser-Nd-YAG
laser
·
Gaseous laser- CO2 laser
·
SemiconductorlaserInjectionlr 45Writesomemedicalapplicationoflasr
·
ENT
·
Dermatology
·
Burn therapy
·
Gynaecology
46.
Define triangle law of
forces
Ans.
Triangle law of forces
states that, if two forces
acting at a point are represented in magnitude and direction by the two adjacent sides of the triangle taken in order,
then the closing
side of the triangle
taken in the reverse order
represents the resultant of the forces in magnitude
and direction.
Where a,b,c are the sides and αβỵ are angle between the sides of a triangle.
47 State Lami’s theorem
Ans.
Lami's theorem states that, if three concurrent forces act on a body keeping it in Equilibrium, then each force is proportional to the sine of the angle between the other two forces.
48. State metal stable state
Ans. Metastable state is an
excited state of an atom or other system with a longer lifetime than the other excited states. However, it has a
shorter lifetime than the stable ground state. Atoms in the metastable state remain excited
for a considerable time in the order of 10-6 to 10-3.
49. Distinguish between spontaneous and stimulated
emission
Ans.
|
S.No |
Spontaneous emission |
Stimulated emission |
|
1 |
The transition of an electron from the excited state
to the ground
state happens as a result
of the natural tendency of the
electron without the action of
any external agent. The radiation
produced as a result of such transitions is called as spontaneous radiation. |
Stimulated emission of radiation is the process
whereby photons are used to
generate other photons that have exact
phase and wavelength as that
of parent photon. |
|
2 |
No external stimuli required. |
Thus stimulated emission is caused by external stimuli. |
50. Distinguish between
concave and convex
lens
Ans.
|
S.No |
Concave |
Convex |
|
1 |
It is thick in the middle
and thin at the edges |
It is thin in the middle
and thick at the edges |
|
2 |
It converges the incident rays towards the principal axis. |
It diverges the incident rays away from the principal axis. |
|
3 |
It has a real |
It has a virtual focus. |
.
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