Heat
Chapter 11
= Question No.1 =
Differentiate between heat and temperature.
Heat
Temperature
Heat is the energy in transit from one body to another due to
temperature difference.
Temperature is the degree of hotness or coldness.
It is the total kinetic energy of the body.
It is the average kinetic energy of the body.
Its unit is Joule.
Its unit is ° C, ° F, and K.
= Question No.2 =
What is meant by the thermal expansion of solid?
Thermal Expansion of solid
Solids expand on heating and their ability to expand depends on their molecular structure. The increase in amplitude of molecules causes an increase in the average distance between
them. Hence solids expands on heating.
= Question No.3 =
How can coefficient of Linear expansion be defined?
Coefficient of Linear Thermal Expansion
Definition
"The change in length per unit length per degree rise in temperature.''
Mathematical Form
Mathematically,
D L = a L1D T------- (I)
Since,
D L = L2 - L1
D T = T2 - T1
Therefore substituting these values in eq(I)
L2 - L1 = a L1(T2 - T1)
L2 = L1 +a L1(T2 - T1)
L2 = L1[1 + a (T2 - T1)]
Units
Units of Coefficient of Linear thermal expansion are 1/° C and 1/K.
= Question No.4 =
What is meant by volumentric expansion?
Coefficient Of Volumetric Expansion
Definition
"The change in volume per unit volume per unit change in temperature.''
Mathematical Form
Mathematically,
Units
The units of coefficient of volumetric expansion are 1/° C and 1/K.
= Question No.5 =
What do you understand by thermal expansion of liquid?
Thermal Expansion of Liquids
Liquids also expand on heating like solids, but expansion in case of liquids is volumetric because liquids have no definite shape and they acquire the shape of the vessel in which they are
poured.
= Question No.6 =
Define Real and Apparent Expansion of Liquide.
Apparent Expansion
Apparent Expansion is the expansion in which only expansion of liquid is considered, expansion of vessel is not considered. So apparent expansion is smaller than real expansion.
Real Expansion
When liquid contained in a vessel is heated not only does the liquid expand but the volume of the vessel also increases. So real expansion is the expansion in which expansion of the
liquid as well as expansion of the vessel is considered.
Real Expansion = Apparent Expansion + Expansion of Vessel
= Question No.7 =
What is anomalous expansion of water with its application.
Anomalous Expansion of Water
Volume of liquids generally increases with increase in temperature. However water behaves differently. As the temperature of the water is raised from 0° C to 4° C water does not
expand but contracts. When its temperature is lowered from 4° to 0° C it expands which is called Anomalous Expansion of Water.
Applications
1.In winter, the water of ponds, lakes and sea in north and South Pole of the earth cools down as the atmospheric temperature falls. As the temperature falls below 4° C the
water at the surface expands, becomes lighter and does not sink. Ice continues to build up at the surface while water near the bottom remains at 4° C. This helps fish and other
forms of marine life to survive in winter season.
2.During rainy seasons lot of water seeps through the cracks in rock in winter when water expands rocks are broken due to this expansion.
3.In cold climate water supply pipes burst when liquid expands on cooling.
= Question No.8 =
How thermal expansion of gases can be explained?
Thermal Expansion of Gases
Gases also expand on heating. Expansion in gases is also volumetric. Unlike liquids and solids, equal volumes of different gases when equally heated undergo almost equal expansion.
= Question No.9 =
What is specific heat?
Specific Heat
Specific Heat is defined as:
"The quantity of heat required to change the temperature of unit mass of substance by one degree celsius."
Mathematically,
Its unit is J/kg.K It does not depend on shape, volume or mass of the object, but only on the nature of the substance.
= Question No.10 =
What is means by law of heat exchange?
Law of Heat Exchange
If two bodies with unequal temperatures are brought in contact with each other, the warmer body loses heat while the cooler body gains heat till both attain the same temperature and
attain the same temperature and attain thermal equilibrium. This is known as law of heat exchange.
Heat lost by hot body = Heat gained by cold body
= Question No.11 =
How specific heat of solids can be determined?
Measurement of Specific Heat of Solids
Calorimeter is used to measure the specific heat of solids. It is made of copper. Following data is obtained in this experiment.
Mass of Inner vessel = m1 kg
Mass of Inner vessel + water = m2 kg
Mass of Inner vessel + water + zinc = m3 kg
Mass of water = (m2 - m1) kg
Mass of Zinc = (m3 - m2) kg
Initial temperature of water and inner vessel = T1° C
Temperature of Zinc = T2 ° C
Temperature of mixture = T3 ° C
Rise in temperature of water and inner vessel = (T3 - T1) ° C
Fall in temperature of Zinc = (T2 - T3) ° C
Specific Heat of inner vessel metal = C1 J/kg K
Specific Heat of Zinc = C2 J/kg K
Specific Heat of water = 4200 J/kg K
Now apply the Law of Heat Exchange:
Heat Lost by Zinc = Heat gained by water + Heat gained by inner vessel
(m2 - m3) (T2 - T3) C2 = 4200(m2 -m1) (T3 - T1) + m1C1(T3 - T1)
All the values are known so specific heat can be calculated.
= Question No.12 =
What do you understand by the term Latent Heat of Fusion and Latent Heat of Vaporization?
Latent Heat of Fusion
"The quantity of heat required to transform one kg of ice completely into water at 0° C is known as Latent Heat of
Fusion."
This heat absorbed by melting ice does not increase the temperature but only helps it to transform from solid to liquid state. This heat actually helps in breaking up bonds of attraction
between other molecules.
Latent Heat of Vaporization
"The quantity of heat energy required to transform 1 kg of water at its boiling point (100° C) completely into gas
(steam) is known as the Latent Heat of Vaporization.''
All the additional heat energy supplied to the boiling water at 100° C is utilized to transform the liquid state of water into its gaseous state.
= Question 13 =
What is the effect of pressure on melting point (Regelation)?
Regelation
The melting point of those materials which expand on being frozen get lowered when pressure over one atmosphere is exerted on them.
Experiment
Take a copper wire with weight on its both ends and place the wire across the block of ice. The copper wire slowly through the block and weight fall to the floor. Large pressure exerted
by the wire slightly lowers the freezing point of ice. So, ice beneath the wire melts water above the wire refreezes this process continues until the wire cuts through the ice block.
= Question No.14 =
What do you know about the effect of pressure on boiling point?
Effect of Pressure on Boiling Point
If the pressure on the surface of a liquid is increased above the normal atmospheric pressure, its boiling point increases. Example air pressure at mountains is lower than at the sea level.
Experiment
Fill a round bottom Flask to half its capacity. After boiling water for couple of minutes remove the burner and cork it. No invert it and pour some cold water on its bottom. After some
time water starts boiling again on cooling. The reason is that since flask is corked so it is not exposed to atmospheric pressure, only pressure which is present is the vapour pressure on
cooling water pressure decreases to such an extent that water starts boiling even at very low temperature.
= Question No.15 =
Explain evaporation. What are the factors on which evaporation depends? Also explain effect of evaporation.
Evaporation
Definition
"Phenomenon of changing of liquids into vapour without boiling is called Evaporation.''
Factors on which Evaporation Depends
It depends upon the following factors:
1.Nature of Liquid
Some liquids have low boiling point, they evaporates much more quickly. Examples are alcohol and ether.
2.Temperature of Liquid
If the surface temperature is high, evaporation rate will increase. Example is ironing of clothes.
3.Surface Area of the Liquids
If the surface area of the liquid is increased, evaporation rate will increase, e.g liquid spread over large area evaporates quickly.
4.Dryness of Air
Drier the air quicker the rate of evaporation. For example in humid weather clothes take much more time to dry.
5.Wind Speed
Higher the wind speed, greater the rate of evaporation.
6.Air Pressure on the Surface of Liquids
If the pressure on the surface of the liquid is lowered, its rate of evaporation shoots up.
Effect of Evaporation
Effect of evaporation is cooling. In evaporation molecules with a lot of kinetic energy escape outside the liquid. Since they take away a lot of kinetic energy from the liquid, the total
kinetic energy possessed by all the remaining molecules decrease. Hence the temperature which is just the measure of average kinetic energy of molecules decreases.
= Question No. 16 =
What is the refrigerator? Write is construction and working.
Refrigerator
Refrigerator is a device which is used for keeping fruits, vegetables and other eatables cool.
Construction
Refrigerator consists of three parts:
1.Evaporator
2.Compressor
3.Condenser
Freon gas is used as a refrigerator
Working
1.The gas is first compressed and fed into the condenser.
2.In condenser it liquefies under pressure.
3.Now this gas is passed through an expansion valve and comes into the evaporator.
4.In evaporator liquid freon evaporates under normal pressure absorbing a lot of heat from the area surrounding the evaporator.
5.Now this freon gas comes into compressor which compresses it into condenser.
6.In condenser it liquefies and delivers the heat taken from cycle.
= Question No.16 =
How many types of thermometer are there?
Ordinary Liquid in Glass Thermometer
The most common type of thermometer is the liquid in glass thermometer. It consists of glass with a capillary tube, having a small bulb at one end. This bulb is filled with liquid. Usually
mercury or alcohol coloured with a red dye to make it visible are used.
Clinical Thermometer
A clinical thermometer is used to find the temperature of the human body. The glass stem of the clinical thermometer has a narrow bend in its capillary. This helps to stop the mercury
thread moving back towards the bulb after the thermometer is removed from the patient's mouth. It range is usually from 35° C to 43° C. (95° F to 110° F)
Maximum and Minimum Thermometer
Maximum and minimum thermometer is used to record the maximum and minimum temperatures reached over a period of time. This thermometer consists of a fairly large cylindrical
bulb, which contains alcohol, and is connected through a U-shaped tube filled with mercury. At the end of this U-tube second bulb is provided.
= Question No.18 =
What are the three numerical scales for temperature?
There are three numerical scales for temperature measurements, namely Celsius, Fahrenheit and kelvin. To assign numerical values to different temperatures, two reference points are
first find. The common reference points for a temperature scale are melting point of ice and boiling point of water.
Celsius
The most commonly used temperature scale is the Celsius and Fahrenheit scales. The Celsius scale, some times called the centigrade scale, has its 0° at the melting point of ice and 100°
at the boiling point of water. The interval between these two points is divided into 100 equal divisions are units.
Farenheit
The Fahrenheit scale is based on the melting point of ice as 32° C and the boiling point of water as 212° F. There are 180 equal divisions are units between these two points.
Kelvin
The third scale of temperature is the Kelvin scale. Its unit is the Kelvin, denoted by symbol K (not ° K) and it has the same magnitude as a degree Celsius.
Interconversion of Temperatures Scale
Kelvin TK = Tc + 273
Fahrenheit TF = 9/5 TC + 273
Centigrade TF = 9/5 TC + 273
= Question No.20 =
What are the three processes by which energy can be transferred from one place to another?
There are three different processes, namely conduction, convection and radiation by which heat energy can be transferred from one place to another.
Conduction
In this process heat energy transfer takes place from atom to atom without the movement of a substance or not from one position to another. Conduction occurs at different rates in
different materials. The ability of a material to conduct heat in fact depends on its atomic or molecular structure. In metals there are a large number of free electrons, which can move
rather freely around. This in addition to molecular collision these free electrons also carry thermal energy from one put to the metal to another, that is only metals are good thermal
conductors. Compared with metals, liquid and gases are poor thermal conductors, because their intermolecular distances are relatively large.
Example
When one end of a long copper rod coated with paraffin wax is placed in a Bunsen flame, the wax will be observed to melt near the flame, and then gradually melt further along the rod.
= Question No.21 =
What are the applications of thermal conduction in our daily life?
Introduction
The good as well as bad thermal conductors have many useful applications in our daily life. Cooking pets and pans are made out of metals so as to conduct heat readily to the food
inside and to spread it evenly. Pot holders and table mats for hot pans etc. On the other hand are made out of cloth and wood or plastic foam i.e. power thermal conductors to avoid
burning of hands and table top etc.
Convection
The transfer of heat by convection requires the movement of molecules from one place to another through large distances. This process of heat energy transfer by the migration of a
substance or bulk movement of a gas or a liquid from one position to another is called convection. Mode of heat transfer is Peculiar to fluid i.e. liquids and gases.
Example
1.Distribution of heat in the earth's atmosphere takes place by winds which blow from the hot regions to the cold ones.
2.Ventilators provided in the walls near the ceiling of a room help to keep the inside temperature moderate.
Radiation
Heat energy from the sun reaches the earth after travelling millions of kilometers in space. It means neither conduction nor convection is involved in the heat transfer from the sun to the
earth. This is in fact achieved by a third mode of heat transfer called radiation in which heat is transferred from one place to another.
The hot objects limit radiation, which carry away energy. When these radiations fall on an object, their energy is transferred to the latter in the form of heat.
= Question No.22 =
Thermoflask
Thermoflask is a pot designed to prevent heat from fluid inside, due to all of the three heat transfer mechanism.
Construction
It consists of a double walled glass vessel, which is silvered on the outer surface of the inner wall and on the inner surface of the outer wall. The glass vessel is enclosed in a metal core
such that it rests on a cork at the bottom of the case, and is secured at the neck with a pad of felt or a ring of rubber.
= Question No23 =
What is thermal conductivity?
The thermal conductivity of a substance is the measure of its ability to conduct heat energy. Experimentally, thermal conductivity can be measured as follows.
Consider a solid slab of thickness of L and face area A, such that its two faces are maintained at temperatures T1 and T2 (T1 x T2)
= Question No.24 =
What is the molecular view of thermal expansion.
As the temperature of a solid is raised the molecules vibrate through large distances. The increase in amplitude of vibration of molecules causes an increase in the average distance
between them. Hence solids expand on heating. Conversely, solids contracts as the temperature is lowered.
= Question No.25 =
What is Bimetallic Strip and what are its applications.
A bimetallic strip is made of pieces of two different metals, iron and brass, attached to each other. When it is heated it bends with the brass on the outside of the curve. Since the outside
of the curve is longer than the inside this down that the brass layer has expanded more than the iron one.
Bimetallic strips are used in many devices, which are in common use.
Bimetal Thermometer
A bimetal strip can be used to make a simple thermometer which is though but every to reed. When the temperature rises, the bimetal strip coils itself into an even tighter spiral due to
different expansion rates of the two metals which form the bimetal strip and the pointer moves arrow the temperature scale.
Thermostat
Thermostat are devices which control temperature in a certain space e.g. in refrigerator, electric ovens, motor car engines etc.
Construction
As temperature of the air inside the room rises. The bimetal strip bends and the electrical contact is disconnected. This switches off the heater. When the room temperature falls, the
bimetal strip cools and straightens. As the contacts touch eacht other, the heater is switched on again.
Fire Alarm
Another very useful application of a bimetal strip is a fire alarm. One end of a bimetal strip is firmly fined while the other end is free. The heat energy given of when a fire starts raises
the temperature of the bimetal strip. The free end of the strip bends towards the contacts and on touching it electric current flows through the circuit.
= Question No.26 =
State Boyl's Law and Charle's Law.
Boyle's Law
Statement
"Volume of a given mole of a gas is inversely proportional to the pressure, if the temperature is kept constant.''
Mathermatical Form
Mathematically, it can be described as:
PV = Constant
Graphical Representation
The graph between pressure and volume of a given mole of gas is a smooth curve showing curve that they are inversely proportional to each other.
Charle's Law
Statement
"The volume of a given mass of a gas is directly proportional to its absolute temperature, provided the pressure of the
gas is kept constant.''
Mathematical Form
Mathematically,
V a T
Graphical Representation
The graph between Volume and temperature of a given mass of a gas is a straight line showing that they are directly proportional to each other.
= Question No.27 =
What is pressure law?
Pressure Law
Statement
"The pressure of a given mass of a gas is directly proportional to its absolute temperature, provided the volume of the
gas is kept constant.''
Mathematical Form
= Question No. 28 =
The three gas laws namely Boyle's Law, Charle's Law and the Pressure Law, can be combined together in the expression.
For 1 mole (the amount of gas is measured in a unit called a mole (mol) which contains a fixed number, called Avogadros Number (NA) of particles of a gas), we have:
PV = RT
Where R is the Universal Gas constant. It has a value of 8.31 mole/K and generally per n moles have:
PV = nRT
Waves and Sound
Chapter 12
= Question No.1 =
Define Simple Harmonic Motion.
The vibratory motion of a mass attached to a spring is called simple Harmonic Motion. The motion in which acceleration is always proportion to its displacement and the acceleration is
always directed towards the equilibrium position is called Simple Harmonic Motion.
= Question No.2 =
Derive the expression of Simple Harmonic Motion.
Simple Harmonic Motion
Consider a block at rest in its equilibrium position on a frictionless block to right, there will be a restoring force F exerted on the block by the spring and this force is directed to the left as
shown in the figure:
According to Hook's Law:
F a -x
F = -Kx
Since direction of displacement is opposite to that of restoring force. According to Newton's Second Law.
F = ma = -Kx
a = -x
This is basic equation of motion for an object undergoing simple harmonic motion. Since:
K = constant
Mass = Constant
Therefore:
a = - (constant) x
a = -(displacement)
= Question No.3 =
Define Simple Harmonic Motion with the Help of Pendulum and Mass Suspended by a Spring.
Simple Harmonic Motion Due to Pendulum
Motion of pendulum is simple harmonic motion because when pendulum is moved from its mean position a restoring force is set which is always opposite to the direction in which it is
displaced.
Simple Harmonic Motion Due to the Mass Suspended By a
Spring
When mass is suspended by a spring and it is moved downwards a restoring force is set which is always opposite to the direction in which is displaced.
= Question No.4 =
Define the Following:
Vibration
"One complete round trip of a body is known as Vibration.''
For example incase of simple pendulum if it is displaced to its max value it will move to other extreme value and returns back to the initial point this is one vibration.
Time Period
"It is the time taken to complete one vibration or oscillation.''
It is measured in seconds.
Frequency
"It is the number of vibration in one second.''
It is expressed as vibration/sec, cycles/sec or Hertz. It is the reciprocal of time period.
Displacement
"Displacement of a vibrating body at any instant is its distance from the equilibrium position at that instant."
Amplitude
"It is the maximum displacement of a body on either side of its equilibrium position."
Wavelength
"The distance below two consecutive crest and trough is called wavelength.''
It is denoted by l and read as Lambda.
Soundwave
"The longitudinal waves that are due to a vibrating source and that are capable of producing a sensation in the auditory
system are called Sound Waves."
Crest
"The projections of the waves are called Crest.''
Trough
"The depressions of the waves are called Trough.''
= Question No.5 =
What is a Ripple Tank?
Ripple Tank
Take some water in a large tray take a meter rod to which a handle is attached. Dip the meter rod in water and move it up and down. As the meter rod vibrates waves once produced
in the form of crest and trough. Place a small cork on the water as the wave pass over the cork, it will vibrate up and down perpendicular to the direction of the waves at is own place.
This shows that as the wave travel along the water surface water particles vibrate perpendicular to the direction of waves, but they do not leave their position.
= Question No.6 =
What is the relation between velocity, wavelength and frequency?
Consider a wave of wave length "l " and frequency "n " travelling with velocity "V" in required medium for the wave to travel a distance of one wavelength so that:
l = VT
The frequency of the wave is naturally determined by the frequency of vibrating particle.
Or,
Substituting the value of "T" in equation.
l = VT
V = n l
= Question No.7 =
What is Resonance? Give its example.
Resonance
When the frequency of the driving force "V" is exactly equal to the natural frequency of the oscillator "n" the driving force imparts the maximum energy to the oscillator resulting in
considerable increase in amplitude of vibration a condition called Resonance.
Resonance occur when ever a system is set in oscillation at its own natural frequency as a result of impulses received from some other system which is vibrating with the same
frequency.
Example
While crossing the bridge, the soldiers are ordered not to march in steps but to break their steps. The reason is that the bridge receives periodic impulses by regular foot steps of a
marching column of soldier if the time period of periodic impulses happens to by equal to the natural time period of the bridge, a vibration of dangerously large amplitude may be
produced and bridge may collapse.
= Question No.8 =
What are the characteristics of sound?
Characteristics of Sound
Following are the characteristics of sound:
1.Intensity and Loudness
"It is the average power crossing a unit area of surface perpendicular to the direction in which the sound waves are travelling."
In M.K.S system unit of intensity is watt per wave is proportional to the square of the amplitude of sound wave.
Loudness is closely related to intensity the loudness "L" and intensity level are related by:
2.Pitch
"The frequency of pure sound is a physical quantity this frequency produces a stimulus to the ear. The sensation corresponding to this is called
Pitch of Sound.''
Pitch of sound depends upon frequency of the vibrating body. Pitch is measured in Hertz.
3.Quality
Ear possesses great sensitivity to quality of sound. It is the quality which makes possible for us to distinguish among the voices of our friend even when they have been distorted by
telephone transmission.
= Question No.9 =
Derive the expression of wave velocity.
The speed of a wave is the distance traveled by it in unit time in the direction of wave.
But,
Hence,
V = fl
= Question No.10 =
What are the two important properties of waves?
Bouncing back of wave from a surface is called reflection. The angle at which the wave is reflected is equal to the angle at which the wave is incident on the surface. Waves coming
from the source and hitting on obstacle in barries called reflected waves have the same frequency because they are produced by the same source.
= Question No.11 =
What do you understand by the term Interference? Explain types of Interference.
Interference
Interference means the interaction of two waves passing through the same require of space at the same time.
When two sets of waves meet, they are neither reflected nor absorbed by each other one simply passes all
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