Nature of Light and Electromagnetics Spectrum,Physics tutors Provider Karachi

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NEWTON’S CORPUSCULAR THEORY OF LIGHT:
Newton put forward a theory, called corpuscular theory of light. According to this
theory “a source of light emits out minute particle called corpuscles. When these
particies reach our eye, they produce the sensation of vision.”
Newton’s explained the following phenomenon of light.
i. The rectilinear propagation of light.
ii. The formation of shadow.
iii. The reflection of light.
iv. The refraction of light.
DEFECT:
To explain the refraction, he made wrong assumption that velocity of light in denser
medium is greater than the velocity of light in air.
WAVE THEORY OF LIGHT:
Huygens put forward a theory called wave theory of light. According to this theory”a
Source of light produces the sensation of vision.”
This theory explained the following phenomenon of light.
i. The rectilinear propagation of light.
ii. The formation of shadow.
iii. The reflection of light.
iv. The refraction of light.
DEFECT:
i. To explain the refraction of light, he made the wrong assumption that velocity
of light is smaller in denser medium, than in air.
ii. According to Huygens a source of light produces the wave sensation of vision
since medium is necessary for the propagation of waves, therefore it was
assumed that the entire space was filled with fluid, called ether.
MAXWALL’S ELECTROMAGNETIC WAVE THEORY:
Maxwell’s put forward a theory called Maxwell’s electromagnetic wave theory.
According to this theory, “Since light is considered as electromagnetic waves because
both have same speed and since electromagnetic waves do not need any medium for
their propagation, “ Therefore light waves can travel in space.
DEFECT:
Maxwell’s electromagnetic theory of light failed to explain the process of photoelectric
effect.
EINSTEIN’S PLANK’S QUANTUM THEORY:
QUANTUM THEORY OF LIGHT:
According to Quantum theory of light, “light are composed of bundles or particles of
energy called proton. The energy of each proton is directly proportional to the
frequency of radiation. “
MATHEMATICALLY QUANTUM THEORY OF LIGHT CAN BE EXPRESSED
AS:
Where,
E : Energy of proton
F ; Frequency of the radiations
H ; plank’s constant, 6.63 x 10-34 js.
DISPERSION:
Definition:
“If phenomenon of spreading of White light into its constituent colours is called
dispersion.”
It is explained by a simple experiment show in the fig when a beam of light (sunlight)
entering a dark room through a narrow hole in a wall, falls on a prism, then on coming
out of the prism forms a band of seven colours on the wall. This multicolor pattern of
light is called spectrum. The colors obtained are Violet, Indigo, Blue, Green, Yellow,
Orange and Red (V.I.B.G.Y.O.R)

RAINBOWS:
Sometimes an arc of beautiful colors appears in the sky after a rainfall. It is seen when
sun on the back side of observer. The rain drop behaves like prism and while light
entering the raindrops is splitted into its constituent’s colors. Such phenomenon of
light i.e. the formation of different colors is rainbow.

EMISSION OF LIGHT BY ATOMS:
According to Bohr’s atomic theory every substance consists of atoms. In an atom the
electron revolve round the nucleus in certain allowed orbit. The energy of the electron
in each orbit has definite value. When electron gain in certain amount of energy if
jumps into the higher orbit. Certain amount of energy it jumps into the higher orbit.
The atom is then said to in exited states. The atoms cannot remain with exited for a
long time. When electron jumps back into the lower orbit it emits energy in the form of
photons. The frequency of such light waves (photons) depends upon the orbit in which
electron transit.
THE ELECTROMAGNETIC SPECTRUM:
The spectrums of electromagnetic radiation consist of radio waves, microwaves, visible
waves, ultraviolet waves, x-rays and r-rays. These electromagnetic radiations have
different in their. Wave length frequencies but all they travel with the speed of light i.e.
3 x 10-8 m/s.
I. RADIO WAVE:
These electromagnetic waves have wave length between few millimeters to
several meters.
II. MICRO WAVE:
These electromagnetic waves have wave length between 1 millimeters to 300
meters.
III. INFRARED:
Infra red waves, also called heat waves, have a mean wave length of 10-5 m.
IV. VISIBLE WAVE:
These electromagnetic waves have wave length ranging from 400 millimeters to
700 nm.
V. ULTRA VIOLET WAVES:
There wave length is between 600 nm to 380 nm.
VI. X-RAYS:
The wave length range is from 109 m to 1011 m.
VII. R-RAYS:
There wave length range is from 1011m to 1014 m.
GREEN HOUSE EFFECT AND GREEN HOUSES:
GREEN HOUSE EFFECT:
“Infra red rays are absorbed by carbon dioxide and water vapors present in the
atmosphere and are not radiated back.”
Heat is trapped in this manner and this effect is known as green house effect.
GREEN HOUSE:
A green glass surface which absorbs infrared radiations is called green house.

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Nature of Heat:
Heat is the transfer of energy (every in transit) from one body to another due to the
temperature difference between the two bodies. When the body absorbs the heat, its
internal energy increases and when it losses heat, its internal energy decreases.
Temperature:
Definition:
“Temperature is the degree of hotness or coolness of a body “.
OR
“The measurement of average translational kinetic energy of the molecules is called
temperature “.
Thermometer:
Definition:
An instrument which is used for the measurement of temperature is called the
nanometer. Any property of a substance which changes uniformly with temperature
can be used to measure the temperature.
Temperature scales:
The three scales commonly used to measure the temperature are:
i. Centigrade or Celsius scale.
ii. Kelvin’s or absolute scale.
iii. Fahrenhelt scale.
1. Centigrade or Celsius scale, in the melting point of ice is taken as 0oC and boiling
point of water is taken as 100oC . The interval between them is divided into 100
equal parts. Each part is called one degree centigrade which is written as 1oC.
2 The lowest temperature which can be reached is –273oC. This temperature is
taken 0oC on Kelvin’s scale. The size of the degree on the scale is also same as
that on centigrade scale.
3 In Fahrenheit scale, the melting point of ice is taken as 32oC and boiling point of
water is taken as 212o, and the internal given then is divided into 180 parts. Each
part is called one degree. Fahrenheit which is written as 1oF.









Inter Conversion of Scale:
The conversion of temperature in centigrade (Tc) into the temperature in Kelvin (Tk) is
performed by the relation.
Tk = Tc + 273
OR Tc = Tk - 273
Temperature in Fahrenheit (Tf) is converted into temperature in centigrade (Tc) by the formula.
Tf = 9 / 5 (Tc) + 32
Tc = 5 / 9 (Tf – 32 )
Ordinary Liquid in Glass Thermometer:
It consist of a glass slem with a capillary tube having a small bulb at one end. The bulb
end part of the capillary tube is filled with liquid (mercury or alcohol). The upper end of
the capillary tube is sealed to prevent the liquid from evaporation. Air is reserved from
the upper end before sealing , when the bulb is sealed , the mercury expands and rise in
the capillary tube. The stem is calibrated in degrees to measure the temperature. The
thermometer used in the laboratory has a range from – 10oc to 110oC.



Clinical thermometer:
Clinical thermometer is used to measure the temperature of human body. The normal
body temperature is about 98.4oF. The bulb of the thermometer is placed under the
tongue to measure the temperature of a body. The clinical thermometer has a narrow
bend or construction in its capillary tube bore near the bulb to prevent the mercury
level from falling when the bulb is removed from the patient’s mouth.


Maximum and Minimum Thermometer:
The purpose of this thermometer is to read
maximum and minimum temperature reached
over a period of time. It consist of a bulb A
continuously alcohol is connected through a
U shaped tube from B to C (containing mercury)
to a second bulb D nearly full with alcohol. Above D,
the space is evacuated.
Left limb of U-shaped tube is calibrated according
to the expansion of alcohol in AB. The right limb of
U-tube is also calibrated. So that both mercury
surfaces point to the same member. If mercury in AB
contracts, the pressure in CD well drive the mercury back.
On each mercy surface, there is a small iron index provided with a spring. Due to fall
in temperature the alcohol in A contracts and the left index moves up and is left there.
Due to rise in temperature, the alcohol in A expands and the right index moves and is
left there. The lower end of left index gives minimum temperature and the lower end
of right index gives maximum temperature over a period of time. The indices are
brought in contact with mercury by using small bouquet.
Transfer of Heat:
There are three ways by which heat is transferred from one place to another. They are
i. Conduction.
ii. Convection.
iii. Radiation.
Conduction:
Definition:
“The process in which heat is transferred from one place to another by the vibration
and collision of molecules or atoms, called conduction.”
Explanation:
When the heat is provided to one end of the heat conductor. Its temperature rise
which increase the kinetic energy of the molecules. Due to increase kinetic energy,
molecules start vibration with greater amplitude and make collision with neighboring
molecules. This collision causes the transference of energy from molecule to molecule.
In this way that is transferred from one end to other.
Example:
Solid heat conductor transfer heat by the process of conductor.
Convection:
Definition:
The process, in which heat is transferred from one place to another by the actual
motion of molecules, is called convection.
Since the molecules of liquids and gases are free to more, therefore in liquid and
gasses heat is transferred from one place to another by convection.
Example:
In fluid (liquids and gasses) heat is transferred by the process of convection.
Radiation:
Definition:
The process in which heat is neither transferred by the vibration and collision neither of
molecules, nor by the actual motion of molecules but it is transferred without any
material medium, is called Radiation.
In this process hot body radiates energy in the form of electromagnetic waves.
Heat reaches from sun to earth, by radiation.
Thermos Flask:
It is used to maintain constant temperature.
A thermos flask consists of a double walled glass.
The inner surface of the outer wall and the outer
surface of the inner wall are polished (silvered).
The space between to the two walls is evacuated and then sealed. The vacuum
between the two walls reduces the probability of transfer of heat by
conduction and convection.
Thermal Conductivity:
Definition:
The ability of a substance to conduct heat energy is called thermal conductivity.
Consider a metal block of length L and the cross section area A,
Such that it one end is constantly maintained at lower temperature
T1 and other end at a higher temperature T2. If Q heat is conducted
from hot end to the cold end in t second, then it is found that.
i. Heat is proportional to the cross sectional area
Q  A.
ii. Heat is proportional to the difference of the temperature.
Q  T OR Q  (T2 - T1)
iii. Heat is proportional to the time of the flow.
Q  t
iv. Heat is inversely proportional to the length
Q  1 / L
Combining them, we get: Q  A (T1 – T2 t
L
Q = K A (T1 – T2 t
L
Q = K A  T t T = T2 - T1
L
The constant K is called thermal conductivity of the material of rod. Different materials
have different value for K.
I f L = 1m
A = 1m2 that is if we take 1 meter cube of the substance)

T = 1oC t = 1 second
Substituting values in 1
Q = K x 1 x 1 x 1 Q = K
It shows that, “the thermal conductivity is the quality of heat conducted per second per
meter cube of a substance whose opposite faces are maintained at a temperature
difference of 1oC “.
Thermal Expansion:
Definition:
Increase in the size of the object due to heat is called thermal expansion.
Thermal Expansion in Solid:
When solid is heated its temperature rises and its molecules start vibrating with greater
amplitude. Due to this, the average distance between the molecules increases and the
solid expands.
There are two expansions in solids.
i. Linear thermal expansion. ii. Volumetric thermal expansion.
Linear Thermal Expansion:
Definition:
“ Increase in the length of the rod due to heat is called linear thermal expansion.”
Consider a metal rod having length L, when the temperature is increased by T, let the
increase be T. It is found that,
L  AL1 L  T
Combining them, we get:
L  L1 T L =  L T
Where “ “ is the coefficient of linear expansion. It can be written as:
 = L
L1 T
It shows that, change in length per unit length per degree rise in temperature is called
coefficient of linear expansion.
Consider L =  L1 T
But L = L2 - L1 & T = T2 - T1
L2 L1 =  L1 (T2 – T1)
L2 = L1 +  L1 (T2 – T1) It gives the final length
L2 = L1 1 +  (T2 - T1) after the rise in temperature.
Volume Thermal Expansion:
Definition:
“Increase in volume of the object (space /cube) due to heat is called volumetric
thermal expansion.”
Consider an object having volume V1. When the temperature is increased by T, let the
Increase by V., it is found that,
V  V1
V  T
Combining them, we get V  V1 T
V =  V1 T
Where “” is the coefficient of linear expansion. Above equation can be written as:
 = V
V1T
It shows that, “change in volume per unit volume per degree rise in temperature is
Called coefficient of volumetric expansion.
Consider: V =  V1T
But V = V2 – V1 & T = T2 – T1
V2 - V1 + V1 (T2 – T1)
V2 = V1 +  V1 (T2 - T1)
V2 = V1 1 +  (T2 - T1 )
It gives the final volume after the rise in temperature.
Relation Between Coefficients of Linear And Cubical Expansions:
The coefficient of volumetric (cubical) expansion is three times the coefficient of linear
expansion. i.e.  = 3
Bimetallic strips:
Two metals of slightly different coefficient of thermal expansitives combined together
to form bimetallic strips when this strips is heated, it bend.
Bimetal strips:
In bi metal thermometer the bimetallic strips is in the form of long spiral whose one
end is fixed and other end is connected to a pointer. When temperature raises the
spiral get into lighter position due to different nature of two metals. Due to this pointer
moves over a scale and gives the temperature.
Thermostat:
A device which is used to maintain the constant temperature is called thermostat.
It is used in refrigerator, air conditioner, electric oven etc. to control the temperature.
Fire Alarm:
The bimetallic strip is also used in fire alarm. Due to fire when the temperature rises,
the bimetallic strip bends and touches the contact due to which the current flows and
either the bulb glows or the bell rings giving the warning about life.
Thermal Expansion of Liquid:
Liquid do not have definite shape. Therefore, there is only one expansion in case of
Liquids. This is called volumetric expansion.
Real and apparent expansion:
When a liquid in a vessel is heated, not only the liquid expands but the vessel also
expands. Thus the observed increase in volume of liquid is not the actual increase in
volume of the liquid because we should consider the increase in volume of the vessel.
Thus, Real expansion = apparent expansion + expansion of the vessel.
Anomalous expansion of water:
When water is heated from 0oC to 4oC the water does not expand but it contracts and
its density increase. When water is further heated from 4 to 100oC, its volume increases
and density decreases. Since volume decreases when the temperature is raised from
0oC to 4oC. Therefore when temperature is lowered from 4oC to 0oC the volume
increases. This is called anomalous expansion of water.
Effect of anomalous expansion of water:
i. In winter season:
At 0oC the surface water of ponds, lakes freezes to ice but at the bottom the
temperature of water remains at 4oC, this helps fish and other forms of marine
life to survive in winter season.
In winter season the water supply pipe lines burst when the temperature falls
below at 4oC. Below 4oC, the water expands and causes the pipeline to burst.
ii. In rainy season:
Lot of water seeps through cracks in rocks, in winter this water expands on
freezing and exerts very high pressure raising the rocks to breaks.
Thermal expansion in gasses:
Gasses also expand on heating. For example, in summer when the temperature is very
high the tubes of bicycles get burst. Due to very high temperature the air in the tube
expands and exerts very high pressure on the walls of the tube, causing it to burst.
Gas laws:
There are four fundamental quantities, pressure, volume, temperature and mass to
explain the behavior of gasses. The relation ship between these quantities.
Boyle’s Law:
Statement # 1:
“When mass and temperature of a gas are kept constant, the volume of a given mass is
inversely proportional to the applied pressure.”
Statement #2:
“When mass and temperature of a gas are kept constant, the product of pressure and
volume always remains constant.”
Statement #3:
If ‘P’ is the applied pressure and ‘V’ is the volume then mathematically Boyle’s law is
given as: V  1/P
V = constant x 1/P
PV = constant
If ‘P1’ and ‘V1’ are the initial pressure and initial volume.
P1V1 = K …………..1
If “P2’ and ‘V2’ are the final pressure and final volume.
P2 V2 = K ………… 2
Equating 1 and 2
P1V1 = P2V2
Charle’s law:
When mass and pressure are kept constant, the volume of a given mass of gas is
directly proportional to the absolute temperature.
Mathematical form:
If ‘V” is the volume and ‘T’ is the temperature then mathematically Charle’s law given are:
V  T
V = KT
V/T = K
If ‘V1’ and ‘T1’ are the initial pressure, volume temperature.
V1 = K ……………………1
T1
If ‘V2’ and ‘T2’ are the initial pressure, volume and temperature.
V2 = K ……………………2
T2
Equating 1 and 2 V1 = V2
T1 T2
Pressure law:
Statement:
When mass and volume of a gas are kept constant, the pressure of given mass of a gas
is directly proportional to the absolute temperature.
Mathematical form:
If ‘P’ is the pressure and ‘T’ is the absolute temperature then mathematically it is given
as: P  T
P = constant T
P = constant
T
General gas equation:
Definition:
The combine mathematical form of Boyle’s law and Charle’s law is called general gas
equation: Fom Boyle’s law PV = K …………………i
From Charle’s law V/T = R ……………….ii
Combining 1 and 2 PV = K …………..1
T
If ‘P1’ , ‘V1 ‘ and ‘T1’ are the initial pressure , volume and temperature.
P1V1 = K …………1
T1
If ‘P2’ , ‘V2’ and ‘T2’ are the initial pressure, volume and temperature.
P2V2 = K …………2
T2
Combining 1 and 2 P1V1 = P2V2
T1 T2
If we take the mass of the gas as 1 mole, can be written as
PV = K
T
Where ‘R’ is the universal gas constant and has a value
R = 8.313 J / mol
Fpr ‘n’ no of moles
PV = nR
T
This is called general gas equation. PV = nRT
Specific Heat:
Definition:
Amount of heat required to raise the temperature of 1kg of a substance by 1K or 1oC is
called specific heat. OR
Amount of heat per unit mass per degree rise in temperature is called specific heat.
Mathematical form:
Mathematically is given as: C = Q
mT
Where C = specific heat Q = amount of heat supplied.
m = mass of substance T = rise in temperature
Above equation can also be written as CmT = Q
Q = CmT
Q = Cm (T2 – T1)
Unit:
The unit of specific heat is J/kgC or j/Kg K
Law of heat exchange:
Heat always from hot body to cold body but the total amount of energy remains same. OR
Heat lost by hot body is equal to the heat gained by cold body.
Thus:

Measurement of specific heat of solid:
An instrument which is used for the measurement of heat is called calorimeter. It is a
copper vessel enclosed in a wooden box insulating material in between. The vessel is
covered by a wooden lid with a hole for the thermometer and another hole for stirrer
to stir the contents of the calorimeter.
The specific heat of solid say zinc can be determined as explained below:
Mass of calorimeter = mc
Mass of calorimeter + water = M
Mass of water = mw = M - mc
Mass of zinc = m
Initial temperature of cal = T1
Initial temperature of zinc = T2
Final temperature of mixture = T3
Specific heat of calorimeter = Cc
Specific heat of water = Cw
Specific heat of zinc = C
According to law of heat exchange Heat lost by = heat gained by
Hot zinc calorimeter + water
Cm(T2 – T3 = Cc mc (T3 – T1) + Cw mw (T2 – T1)
C = (Ccmc + C wmw) (T3 – T1)
M (T2 – T3)
Above relation is used to determine the specific heat of zinc.

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Q1. What is meant by Matter?
Ans: MATTER:
Any thing which has mass and occupied space is called Matter.
Example:
Table, book, earth and etc.
Q2. Give the molecular theory of Matter?
Ans: MOLECULAR THEORY OF MATTER:
i. According to this theory, matter is made of tiny particle called Molecules and
atoms.
ii. The molecules of matter are in c continues and rapid motion.
iii. The difference between solid, liquid and gases states are due to the distance
between the molecules and due to violent motion of the molecules.
Q3. How many state of matter are?
Ans: There are three state of matter.
(i) Solid (ii) Liquid (iii) Gas
Q4. Give the molecular theory of Solid.
Ans: MOLECULAR THEORY OF SOLID:
I. In solids, the molecules are closely packed due to the strong force of attraction.
II. Molecules cannot move freely but they can move to and fro about their mean
position.
iii. Solids have definite volume and shape due to their force of attraction and very
Tiny space between them.
iv. It is not easy to compress solid but they broken down.
Q5. Give the molecular theory of Liquids.
Ans: MOLECULAR THEORY OF LIQUIDS:
i. The liquid molecules can move freely from one place to another place as
compared to solids.
ii. Liquids have definite volume due to some force of attraction between their
molecules, but no definite shape due to weak force of attraction between their
molecules.
iii. The distance between liquid molecules is larger as converted to solid molecules.
Q6. Give the molecular theory of Gases.
Ans: MOLECULAR THEORY OF GASES:
I. Gases have no definite shape and volume because of very large distance
between their molecules and very least force of attraction between their
molecules.
ii. The force of attraction can be negligible between gases molecules due to this
the gases molecules can freely move from one place to another.
iii. The molecules of a gas collide with one another and with the walls of the
container and exert pressure on the walls.
iv. Gases expand on heating because the kinetic energy of molecules is increased
and distance between them is also increased.
Q7. Differentiate between solids, Liquids and Gases.
Ans: SOLIDS LIQUIDS GASES
(i) They have definite shape and volume.
(ii) The molecule of solids have vibratory motion.
(iii) They have greater .density.
(iv)The distance between molecules solids is
very short (i)They have definit volume but
not shape.
(ii)The molecules of liquids have random motion.
(iii)They have low density as compared to solids.
(iv)The distance between Molecules of liquids is greater than solids. (i)They have not definite shape and volume.
(ii)The molecules of gas moves in a straight line.
(iii)They have very low density as compared to solids and liquids.
(iv)The distance between Molecules of gases is much
Greater than solids & liquids.
Q8. What is meant by Brownian motion?
Ans: Brownian motion:
In 1827, a scientist named Robert Brown observed
the movement of dust particles in air seem to very
irregular motion. He also observed the movement
of pollen grains suspended in water with a microscope
and noticed that they were continuously moving in
zig zag path as shown in figure. The zig zag motion
of these particles is called Brownian motion.
Q9. Define Elasticity and Elastic Limit with example.
Ans: Elasticity:
First Definition:
If we apply a force to pull rubber band, it is stretched. When the force is removed. The rubber band comes to its originals shape. This behaviour of any body is called Elasticity.
Second Definition:
Such characteristic of matter in which it tends to oppose every deforming force is
called Elasticity.
Examples:
(i) If a wooden meter rod can bent into an arc by applying force. When force is
removed, it straightens
(ii) Similarly, elasticity is also present in steel rod.
ELASTIC LIMIT:
If we bent a wooden meter into an arc and increases our force then at certain stage the
wooden meter can be break. It means we reached at the elastic limit of wooden meter.
So, it is defined as:
“Such maximum force applied by a body to oppose, every deforming force is called
elastic Limited.”
If we increase our force from elastic limit of a body then it does not comes to its
original position.
Q10. Explain elasticity of bodies on the basis of molecular theory.
Ans: EXPLANATION OF ELASTICITY:
i. Due to very small distance between the molecules of a solid, there is quite strong force between the molecules and they are closely packed..
ii) If a certain force is applied on a body ,then it changes the place of molecules.
Therefore, change in shape volume or length may take place. When force is withdrawn the molecules may become the original place due to strong internal
molecular force of attraction.
iii) Elasticity of a body depends upon the nature of a body. For example, the force,
of attraction between rubber molecules is less as compare to steel. So, less force
is required to deformate rubber as compared to steel..
Q11. Define deformation. Explain with the types.
Ans: DEFORMATION:
If a force is applied on a body to change the shape, then that state is called Deformation.
TYPES OF DEFORMATION:
Linear Deformation:
If a force is applied on a body to change in length, then this state is called Linear
Deformation.
Cubic Deformation:
If the volume of a body change due to applying force, then that state is called Shearing
Deformation.
Q12. Define Stress. Give its unit in different systems.
Ans: STRESS:
When a force is applied to change the length, volume or shape of a body. The value of
This force per unit area is called Stress.
OR
“The magnitude of force applied per unit area of the body is called Stress.”
Mathematically:
It a force “F” Newton is applied on unit area “A”. The stress can be written as
Stress = Force
Area
 = F
A
Where  Greek word is called “ETA”.
SYSTEMS UNITS OF STRESS
S.I.System
C.G.S. System
B.E - System Newton / metre2 or N/m2
Dynes / centimetre2
Lbs / ft 2

Q.13. Write the types of Stress.
Ans: There are three types of Stress.
i. Linear Stress.
ii. Cubic Stress.
iii. Surface Stress.
1. Linear Stress:
When change in length of a body, due to stress is called Linear Stress.
2. Cubic Stress:
When change in length, width and height of a body due to stress is called Cubic Stress.
3. Shearing Stress:
When change in surface of a body due to stress is called Shearing stress.
Q14. What is meant by Strain and Longitudinal Strain?
Ans: STRAIN:
“Such change in volume, length or shape produced by Stress is called Strain.”
LONGITUDINAL STRAIN:
The ratio between the change in length and original length is called Longitudinal Strain
or Linear Strain.
Mathematically:
If “L” is the original length and “ I “ is change in length of a body then,
Strain = Change in Length
Original Length
Strain = I / L
Where “Є” denotes Strain.
Є = I /L
UNIT:
Strain has not unit because it is a ratio between two similar quantities.
Q15. Differentiate between Stress and Strain.
Ans:
STRAIN STRESS
1. It is the ratio between changed in
length per unit original length.
2. It is a ratio between two quantities,
3. It has no unit.
4. Its formula is ∊ = ∆L/L 1. The force per unit area of a body is
called stress.
2. It is a scalar quantity.
3. In S.I system, its unit is N/m2
4. Its formula is  = F
A
Q16. State Hook’s law. Explain with the help of Graph.
Ans: SATEMENT:
The law state the within elastic limit the deformation of body is directly proportional to
the force producing it. “ OR “
In an elastic limit, Stress is directly proportional to strain the relation is called Hook’s
Law.
Mathematically:
Stress  Strain
Stress = Cons tan t (Strain)
Constant = Stress
Strain
Hook’s law also defined as “The force acting on a body is directly proportional to
Deformation within elastic limit.”
F  -x
F = kx
Where “k” is Hook’s constant and x is deformation.
EXPLANATION OF HOOK’S LAW BY GRAPH:
In this graph, if we increase stress then strain will also increase. Even a body reaches to
A point “ x “ , here elasticity maintained. If stress kept continues then the body will go to
Plastic region. It means elasticity of elastic body finished. In plastic region, we increased
More stress then the body will break. The point is called Breaking point. The above
Graph proved the following point.
i. Stress is directly proportional to Strain.
ii. More Stress finished the elasticity of a body.
iii. To known about elasticity of a body.

Q17. State the law of Young’s Modulus and verify Hook’s law.
Ans: YOUNG’S MODULUS:
The ratio between Stress and Longitudinal strain is called Young’s Modulus.
Mathematically:
Young’s Modulus = ____ Stress _
Longitudinal Strain
Y = 

 = ∆L
L
 = F
A
So, equation (i) becomes,
Y = 
¬ ∈
Y = F ÷ AL
A L

Y = F X L
A AL
Y = FL
A ∆L1
Where Y is denoting Young’s Modolus.

VERIFICATION OF THE HOOK’S LAW
According to Hook’s law
Stress  Strain
E  AL
A L
For an elastic limit, the above equation becomes
F = K L
A L
F = AK L
L
F = AK L Where AK = constant
L L
F = (Constant) L
F  L
Q18. Write the characteristics of stationary liquids.
Ans: Characteristics of Stationary Liquids:
i. The pressure exerted by the liquid acts perpendicular to the walls of vessel in
which it is kept.
ii. Pressure exerted on the liquid is transmitted equally in all directions.
iii. In liquids, the pressure at the same depth is equal in all directions.
Q19. Define and explain Pressure. Give its unit in different system?
Ans: Pressure:
The perpendicular force acting on the unit area of a body is called Pressure.
Explain:
i. If we push a drawing pin with a sharp pointed tip into a piece of wood. It will
penetrate the wood.
ii. Under the tip of the drawing pin the force is very high on the small area of the
tip of the pin. Hence it penetrates into the wood.
iii. Now it is difficult to cut things with a blunt knife because the area of the blunt
edge of the knife is relatively more and the force over this area is less as
compared to the sharp edge.
Mathematically:
Pressure = Force / Area
P = F / A
SYSTEM UNITS OF PRESSURE
M.K.S. System
S.I. System
C.G.S. System
B.E. System Newton / metre2 or N/m 2
Pascal (Pa)
Dynes / centimeter 2
Lbs/ft 1






Q20. What is meant by Pressure of Liquids and on what factors does it depend?
Ans: PRESSURE OF LIQUIDS:
Water contained in a glass has weighed. As the weight is a force what acts downward,
therefore the water exerts a pressure on the bottom of the glass. Similarly, every liquid
exerts force per unit area of container, which is called Pressure of Liquid.
Pressure of Liquids depends upon following factors:
i. Density of Liquid:
If a liquid more dense then pressure is more.
ii. Depth of Liquid:
If the depth of liquid is greater than the pressure is greater.
Q21. Prove that the pressure of liquids depends upon density and depth or P = phg.
Ans: Suppose water contained in a gas, exerts force per unit area is called Pressure. If “F” is
force, “A” is area and Pressure is “P” then.
P = F / A ________________1
We know that
F = mg ________________2
Mass per unit volume is called Density and it is denoted by (RHU) OR “p “
P = m / V
M = Pv
The volume is, V = Length x Width x Height
V = L x W x h
V = A x h
So, m = P (A x h) put in equation – No.2
F = mg
F = P (A x h)g
Now put the value of “F” in equation No.1
P = p (A x h)g
A
P = phg
Where “p” is density, h = depth, g = acceleration due to gravity. Hence it proved the
pressure of liquid depends upon depth and density.

Q22. Give the principle of Pascal.
Ans: PRINCIPLE:
According to this principle, if a pressure is applied to a liquid contained in a vessel, it is
transmitted pressure equally in all direction and acts perpendicularly to the walls of the
container. This was discovered by Blaise Pascal, and is known as Pascal’s Principle.
Explanation:
It is explain with the help of following experiment.
Experiment:
i. Take a vessel which is connected with four
Similar pistons.
ii. Fill it with water.
iii. Apply a force to one end of the pistons.
iv. The other three pistons simultaneously
move through small distance outwards.
v. Thus it can be proved that the pressure
has been transmitted in all directions
throughout the water.

Q23. How many types of Hydraulic Machines.
Ans: TYPES OF HYDRAULIC MACHINES:
There are three types of Hydraulic Machines.
i. Hydraulic Break system.
ii. Hydraulic Lifts.
iii. Hydraulic Press.

Q24. What do you know about Hydraulic break system.
Ans: HYDRAULIC BREAK SYSTEM:
System is used in vehicle,
consists of a master cylinder joined by
tubes to four smaller cylinder, one for
each wheel of vehicle. The master
cylinder and each of the brake cylinders
are provided oil tight pistons.
When we push on the brake pedal it
causes a force on the piston in the
master cylinder. This pressure
transmits equally in all directions.
This pressure effects the points present in the wheel cylinder. These pistons force the
brake shoes to expand and resulting friction stops the wheel. It is an example of
Pascal’s Law.
Q25. Write note on Hydraulic Press.
Ans: HYDRAULIC PRESS:
The working of hydraulic press is same
hydraulic lift, in a hydraulic press the
piston ‘B’ is used to compress any material
over it a rigid roof material is placed
between roof and piston ‘B’. When force is
applied on piston ‘n’ then B moves upwards.
It compresses cotton into a compact bale.
Q26. Write short note on Hydraulic lift.
Ans: HYDRAULIC LIFT:
In Hydraulic lift, narrow cylinder ‘A’ connected with wider cylinder B and they are fitted
with air tight pistons.











It is filled with some incompressible fluid. By pressing cylinder ‘A’, the pressure is
transmitted equally according to Pascal’s principle to the piston of the cylinder ‘B’ and
B moves upward. The piston ‘B’ is used as a platform for a car or any heavier object to
be lifted.
Q27. What is meant by Pressure of gases? On what factor it depends?
Ans: PRESSURE OF GASES:
When a gas is closed in a cylinder in a container, then molecules of gas collide with
each other and also strike against the walls of the container. During collision, the
molecules exert force per unit area of container, this force is called Pressure of gases.
FACTORS ON WHICH PRESSURE OF GASES DEPENDS:
The pressure of gases depends upon the following two factors:
i. Volume of Gas
If the volume of gas is greater then pressure is increased.
ii. Temperature of Gas
If the temperature of a gas is increased then the molecules of gas collide with
The walls firstly and exerted greater pressure on the walls of container.
Q28. Explain Atmospheric pressure. Give also the experiment of Von Guericke.
Ans: ATMOSPHERIC PRESSURE:
The air is mixture of Nitrogen, Oxygen and many other gases. These gases exerts
pressure is called Atmospheric pressure.
The density of air changes from sea level to different altitudes. It is most dense at sea
level, its density decreases with increase of height above sea level.
At sea level the pressure of air is about 100,000 Pa. We do not normally feel
atmospheric pressure as the pressure inside our bodies is almost the same as that
outside.

EXPERIMENT OF VON GGUERICKE:
i. The existence of atmospheric pressure
was first performed by a German scientist
Von Guericke.
ii. He took two hollow metallic hemispheres
which were made to fit with each tightly.

iii. Air inside the hemispheres was removed
through a small hole by means of an air pump.
iv. It was found that the hemispheres could not be pulled apart when the air had
been removed.
v. The hemispheres were so tightly hold that it looks two teams each of eight
horses to separate them.

Q29. What is barometer and how many types of Barometer are.
Ans: BAROMETER:
A device for measuring the atmospheric pressure is called barometer. There are two
types of Barometer.
(i) Mercury Barometer (ii) Aneroid Barometer

Q30. Write a note on Mercury barometer.
Ans: MERCURY BAROMETER:
Atmospheric pressure is measured in a laboratory
by a device called Mercury Barometer.
CONSTRUCTION:
A barometer consists of a thick walled glass tube
1 meter length which is opened at one end and
closed from the other side. To start with the tube
is filled with mercury. The open end is firmly covered
with a thumb and then carefully inverted in a vessel
containing mercury. Some of the mercury from the
leaving a space at the closed end. It is found to be
approx. 760 mm. The length of mercury in tube equal
to the atmospheric pressure.

Q31. Write note on Aneroid Barometer.
Ans: ANEROID BAROMETER:
The aneroid barometer is commonly used for household i purposes. It consists of a
corrugated steel box ‘A’ partially evacuated of air. The top of the box pressure against
a strong spring ‘S’. If the air pressure rises, the top of the bon is pressed inwards and
If the pressure decreases the top moves upwards. The movement of the top due to
changes in pressure is magnified by a system of lever connected to a small rod fixed on
the top of ‘A’. The movement of the lever enables a printer ‘P’ to move over a suitable
calibrated scale.
Q32. Write the application of atmospheric pressure.
Ans: The following are uses of atmospheric pressure.
(i) It is used to make siphons. Ii) It is used to make pumps.
(iii) It is used to make syringes.
Q33. State Archimedes Principle.
Ans: ARCHIMEDES PRINCIPLE:
When a body is wholly or partially immersed in a liquid, then a force acts on the lower
surface of the body, this force equal to the volume of body and called upward thrust.
So, a body immersed in a liquid it experiences and upward thrust equal to the weight
of the liquid these its weight is decreased in water. This principle was first observed by
Archimedes. So it called Archimedes Principle.
Q34. Give the experimental proof of Archimedes Principle.
Ans: EXPERIMENTAL PROOF OF ARCHIMEDES PRINCIPLE:
For experimental verification of Archimedes Principle, consider the following experiment.
Consider a cylindrical object of area ‘A’ and height ‘h’ immersed in a liquid of density p;
four sides for acting on that body in which two from left and right and other two
from up and downward. The force acting from left and right cancel the effect of each
other and also up downward forces do the same. The force acting upon surface of a body.
The force acting upon surface of a body F1 = Ah1pg + Apa
The force acting lower the surface of the body.
F2 = Ah2pg + Apa
Upthrust = F2 F1
Upthrust = (Ah2pg + Apa) - (Ah1pg + Apa
Upthrust = Ap2pg + Apa Ah1pg – Apa
Upthrust = Ah2 pg - Ah1pg
= Ap(h2 h1)g
= Aphg
= pg(I x h x w )
= pgV
We know that Mass
density = volume
p = m
V
PV = m
Put the value in equation (i)
Upthrust = pVg
= mg
Upthrust = W W = mg
Uthrust = Weight of the body.
We can now draw the following conclusions for floating bodies in fluids.
i. The up-thrust force depends upon density an volume.
ii. Up-thrust force equal to the weight of the body.
iii. These results prove Archimedes Principle.
Q35. Write the conditions fro the floatation of the bodies.
Ans: CONDITIONS:
i. If the weight of the body is greater than the upward thrust the body will sink in
the liquid which is providing upward thrust.
ii. If the weight of body is less than the upward thrust, the body will rise up and
float on the surface of the liquid..
iii. If the weight of the body is equal to the upwards thrust the body will float
partially immersing into the liquid.
Q36. Explain why an Iron ship floats while a piece of stone sinks in water.
Ans: A ship is constructed in ship in such a way that the density of the ship be will less than
the density of water displaced by it to move over. The volume of ship is very large and
hence the upward thrust on it is also very large. This upward thrust not only neutralizes
the weight of ship but provides some additional upward force on the ship. The ship,
therefore, does not sink in water.
A piece of stone sinks in water because its weight is greater than the upward thrust of
water.
Q37. Write the condition for the motion of submarines in water.
Ans: CONDITION FOR THE MOTION OF SUBMARINES IN WATER:
Submarines can float on the surface of water and when is needed they can dive in
water. Submarines are fitted with large hollow ballast tank. To dive in water, the
submarine takes water into its hollow tanks. This increases the weight of submarine and
it submerges in water.
Diving submarine: