Thermal Energy
Thermal Expansion of Solids
Expansion of Solids
Demonstrate expansion of solids
When a solid is heated one or more of the following may occur:
- Its temperature may rise
- Its state may change
- It may Expand
Expansion of solids is the increase in dimensions of a solid when heated.
Contraction of solids is the decrease in dimensions of a solid when is cooled.
DEMONSTRATION OF EXPANSION OF SOLIDS
In order to demonstrate the expansion of solid we can use following method
- The ball and Ring Experiment
- The Bar and Gap Experiment
The ball and Ring Experiment
1st Case: When the ball is not heated then it will pass through the ring very easily because it has a small volume.
2nd Case: When the ball is heated, it will expand and increase in volume, so itwill not pass through the ring.
The Bar and Gap experiment
1stCase:When the Bar not heated (Not raised with temperature) then the dimension will remain constant.
2nd Case:When
the Bar is heated (raised with temperature) then the dimension of the
Bar will increase and eventually will not pass thought the Gap.
the Bar is heated (raised with temperature) then the dimension of the
Bar will increase and eventually will not pass thought the Gap.
Expansion of Solids in terms of Kinetic Theory of Matter
Explain expansion of solids in terms of kinetic theory of matter
When asolidis
heated, its atoms vibrate faster about their fixed points. The relative
increase in the size of solids when heated is therefore small. Metal
railway tracks have small gaps so that when the sun heats them, the
tracks expand into these gaps and don’t buckle.
heated, its atoms vibrate faster about their fixed points. The relative
increase in the size of solids when heated is therefore small. Metal
railway tracks have small gaps so that when the sun heats them, the
tracks expand into these gaps and don’t buckle.
Forces due toexpansion
Normally
Expansion and contraction is accompanied by tremendous forces; The
presence of force indicates the expansion and contraction is Resisted.
Expansion and contraction is accompanied by tremendous forces; The
presence of force indicates the expansion and contraction is Resisted.
Bar breaker
- Consists
a strong metal blocker with a pair of vertical jaws J and a strong
metal Bar R. The metal bar has a wing nut N at one end and an eye at the
other end. - The bar is placed between the two pair of Jaws
- A short cast iron C is inserted in the eye of the bar.
- The bar is then heated it expands and the wing not screwed to tighten the bar R against the jaws.
- The
bar is then allowed to cool as it cools, it contracts the short cast
Iron rod C which presses against the jaws of the bar breaker, Resists
the contraction of the Metal bar R. - The resistance to the
contraction of the bar sets up very large forces which breaks the short
cast Iron rod C in the eye of metal bar, Because the contracting bar is
trying to pull itself through the small gap in the frame.
Expansivity of Different Solids
Identify expansivity of different solids
The coefficient of linear expansion or linear expansivity (x)
The amount by which the linear dimension of a given solid expands depends on:
- The length of the solid
- The temperature to which the solid is heated
- The nature of solid
Coefficient
of linear Expansivity (x) is the fractional increase in length of the
solids per original length per degree rise in temperature.
of linear Expansivity (x) is the fractional increase in length of the
solids per original length per degree rise in temperature.
Mathematical formula
Thus
SI Unit of coefficient of linear expansivity (X) is per degree centigrade ºC -1
Example 1
A
copper rod has a length of 40cm on a day when the temperature of the
room is 22.3ºC. What will be its length become on a day when the
temperature of the room is 30ºC ? The linear expansivity of copper is 0.
000017/ºC
copper rod has a length of 40cm on a day when the temperature of the
room is 22.3ºC. What will be its length become on a day when the
temperature of the room is 30ºC ? The linear expansivity of copper is 0.
000017/ºC
Solution
Table which shows the coefficient of Expansivity Constant.
| Substance | Linear Expasivity (PerºC) |
| Aluminum (Al) | 0.000026 |
| Brass | 0.000019 |
| Copper | 0.000017 |
| Iron | 0.000012 |
| Steel | 0.000012 |
| Concrete | 0.000011 |
| Glass | 0.0000085 |
| Invar ( Alloy of Iron and Nickel) | 0.000001 |
The Application of Expansion of Solids in Daily Life
Explain the applications of expansion of solids in daily life
There
is a large number of important practical applications of thermal
expansion of solids; While laying the railway tracks, a small gap is
left between the successive lengths of the rails. This will allow
expansion during a hot day. The iron tyre is to be put on a wheel, the
tyre is first heated until its diameter becomes more than that of the
wheel and is then slipped over the wheel.
is a large number of important practical applications of thermal
expansion of solids; While laying the railway tracks, a small gap is
left between the successive lengths of the rails. This will allow
expansion during a hot day. The iron tyre is to be put on a wheel, the
tyre is first heated until its diameter becomes more than that of the
wheel and is then slipped over the wheel.
Thermal Expansion of Liquids
The Apparent Expansion of Liquids
Explain the apparent expansion of liquids
Liquids
expands when heated and contracts when cooled. It is easier to observe
expansion in liquids than in solids. Different liquids expand at
different rates in response to the same temperature change. Liquids
expand much more than solids for equal changes of temperature. Apparent
expansion of liquids is always less than the true expansion of the
liquid.
expands when heated and contracts when cooled. It is easier to observe
expansion in liquids than in solids. Different liquids expand at
different rates in response to the same temperature change. Liquids
expand much more than solids for equal changes of temperature. Apparent
expansion of liquids is always less than the true expansion of the
liquid.
Demonstrate the Effects of Heat on Liquids
Demonstrate the effect of heat on liquids
Liquids
unlike solids can be poured. If a liquid is poured into a vessel, it
takes the shape of the vessel. For this reason a liquid can’t have
linear and aerial expansivity, thus liquids have only volume
expansivity. Liquids molecules have kinetic energy. This energy
increases if the temperature of the liquid is raised by heating. Heating
causes the molecules of liquid to move faster.
unlike solids can be poured. If a liquid is poured into a vessel, it
takes the shape of the vessel. For this reason a liquid can’t have
linear and aerial expansivity, thus liquids have only volume
expansivity. Liquids molecules have kinetic energy. This energy
increases if the temperature of the liquid is raised by heating. Heating
causes the molecules of liquid to move faster.
Activity 1
Items Needed
- Large heat safe glass bowl
- Cooking Oil
- Food Coloring
- Two 2×4 blocks
- Candle
- Match or Lighter
Instructions
- Begin by filling a large glass bowl with cooking oil.
- Next, add between 5-10 drops of food coloring into the oil. Helpful Tip: Place the drops near the center of the bowl.
- Prop the bowl up off the table using two 2×4 blocks.
- Light a candle and carefully place it under the bowl. The flame of the candle should touch the bottom of the glass bowl.
- Look
through the side of the glass bowl and watch carefully to observe what
happens. Helpful Tip: It will likely take 5 minutes before you see
anything happen to the liquid/food coloring.
You can alternatively follow the experiment through the following vedio
Verification of Anomalous of Water
Verify the anomalous expansion of water
The
instrument used to demonstrate anomalous expansion of water is called
hope’s apparatus. it consists of a brass cylinder, jacket J with a
mixture of ice and salt and two thermometers A and B at regular
intervals upward and at the bottom.The hope’s experiment shows that
water contracts as it cools down to 4 degree centigrade and then expands
as it cooled further below 4 degree centigrade.
instrument used to demonstrate anomalous expansion of water is called
hope’s apparatus. it consists of a brass cylinder, jacket J with a
mixture of ice and salt and two thermometers A and B at regular
intervals upward and at the bottom.The hope’s experiment shows that
water contracts as it cools down to 4 degree centigrade and then expands
as it cooled further below 4 degree centigrade.
In
the year 1805, the scientist T. C. Hope devised a simple arrangement,
known as Hope’s apparatus, to demonstrate the anomalous behaviour of
water.
the year 1805, the scientist T. C. Hope devised a simple arrangement,
known as Hope’s apparatus, to demonstrate the anomalous behaviour of
water.
Hope’s
apparatus consists of a long cylindrical jar with two openings on the
side, one near the top and the other near the bottom to fit thermometers
in each of these openings. A metallic cylindrical air-tight trough with
an outlet is also fitted onto the jar, on its central portion. Two
thermometers are fitted air-tight in the two openings of the cylindrical
jar. The thermometer near the bottom of the jar is T1, and the one near the top of the jar is T2.
Now the cylindrical jar is filled with water. The cylindrical trough at
the central portion of the jar is filled with a freezing mixture of ice
and common salt.
apparatus consists of a long cylindrical jar with two openings on the
side, one near the top and the other near the bottom to fit thermometers
in each of these openings. A metallic cylindrical air-tight trough with
an outlet is also fitted onto the jar, on its central portion. Two
thermometers are fitted air-tight in the two openings of the cylindrical
jar. The thermometer near the bottom of the jar is T1, and the one near the top of the jar is T2.
Now the cylindrical jar is filled with water. The cylindrical trough at
the central portion of the jar is filled with a freezing mixture of ice
and common salt.
The Application of Expansion of Liquids in Everyday Life
Explain the applications of expansion of liquids in everyday life
Water
in lakes and ponds usually freezes in winter. Ice, being less dense
floats on the water. This insulates the water below against heat loss to
the cold air above. Water at 4 degree centigrade being most dense,
remains at the bottom of the lake, while ice, being less dense than
water floats on the layers of water. This enables aquatic animals to
survive in the water below the ice.
in lakes and ponds usually freezes in winter. Ice, being less dense
floats on the water. This insulates the water below against heat loss to
the cold air above. Water at 4 degree centigrade being most dense,
remains at the bottom of the lake, while ice, being less dense than
water floats on the layers of water. This enables aquatic animals to
survive in the water below the ice.
The Concept of Thermal Expansion of Gases
Explain the concept of thermal expansion of gases
Gases
expand when heated just like solids and liquids. This is because the
average kinetic energy of the molecules in a gas is directly
proportional to the absolute temperature of the gas. Heating the gas
increases the kinetic energy of its molecules, making them vibrate more
vigorously and occupy more space.
expand when heated just like solids and liquids. This is because the
average kinetic energy of the molecules in a gas is directly
proportional to the absolute temperature of the gas. Heating the gas
increases the kinetic energy of its molecules, making them vibrate more
vigorously and occupy more space.
The Relationship between Volume and Temperature of Fixed Mass of Air at Constant Pressure
Investigate the relationship between volume and temperature of fixed mass of air at constant pressure
Three
properties are important when studying the expansion of gases. These
are; pressure, volume and temperature. Charles law states that the
volume of a fixed mass of gas is directly proportional to the absolute
(Kelvin) temperature provided the pressure remains constant.
Mathematically V1T2 = V2T1.
properties are important when studying the expansion of gases. These
are; pressure, volume and temperature. Charles law states that the
volume of a fixed mass of gas is directly proportional to the absolute
(Kelvin) temperature provided the pressure remains constant.
Mathematically V1T2 = V2T1.
Example 2
the
volume of gas at the start is recorded as 30 cm3with a temperature of
30°C. The cylinder is heated further till the thermometer records 60°C.
What is the volume of gas?
volume of gas at the start is recorded as 30 cm3with a temperature of
30°C. The cylinder is heated further till the thermometer records 60°C.
What is the volume of gas?
Solution:
We know,V/T = constant
therefore,
V1/T1=V2/T2
V1 =30 cm3
T1 =30°C = 30+273 = 303K(remember to convert from Celsius to Kelvin)
T2 =60°C = 60+273 = 333K
V2 =?
V1/T1=V2/T2
V2=V1xT2/T1
V2=30×333/303
= 32.97 cm3
The Relationship between Pressure and Volume of a Fixed Mass of Air at Constant Temperature
Investigate the relationship between pressure and volume of a fixed mass of air at constant temperature
The
relationship obtained when the temperature of a gas is held constant
while the volume and pressure are varied is known as Boyle’s law.
Mathematically, P1V1 = P2V2. Boyle’s law states that the volume of a
fixed mass of gas is inversely proportional to its pressure if the
temperature is kept constant.
relationship obtained when the temperature of a gas is held constant
while the volume and pressure are varied is known as Boyle’s law.
Mathematically, P1V1 = P2V2. Boyle’s law states that the volume of a
fixed mass of gas is inversely proportional to its pressure if the
temperature is kept constant.
PressurexVolume = constant
pxV = constant
Example 3
The volume of gas at the start is 50 cm3with a pressure of 1.2 x 105Pascals. The piston is pushed slowly into the syringe until the pressure on the gauge reads 2.0 x 105Pascals. What is the volume of gas?
Solution:
We know
p x V = constant
therefore,
p1xV1= p2xV2
p1=1.2 x 105Pascals
V1=50 cm3
p2=2.0 x 105Pascals
V2=?
p1xV1= p2xV2
V2=p1xV1/p2
V2=1.2×105x50/2.0 x 105
V2= 30 cm3
The Relationship between Pressure and Temperature of a Fixed Mass of Air at Constant Volume
Investigate the relationship between pressure and temperature of a fixed mass of air at constant volume
To
investigate the relationship between the pressure and the temperature
of a fixed mass, the volume of the gas is kept constant. The pressure is
then measured as the temperature is varied. P1/T1 = P2/T2 ,this is
called pressure law. The pressure law states that the pressure of a
fixed mass of a gas is directly proportional to the absolute temperature
if the volume is kept constant
investigate the relationship between the pressure and the temperature
of a fixed mass, the volume of the gas is kept constant. The pressure is
then measured as the temperature is varied. P1/T1 = P2/T2 ,this is
called pressure law. The pressure law states that the pressure of a
fixed mass of a gas is directly proportional to the absolute temperature
if the volume is kept constant
Example 4
Pressure of gas is recorded as 1.0 x 105N/m2at a temperature of 0°C. The cylinder is heated further till the thermometer records 150°C. What is the pressure of the gas?
Solution:
We know,p/T = constant
therefore,
p1/T1= p2/T2
p1=1.0 x 105N/m2
T1=0°C = 0+273 = 273K(remember to convert from Celsius to Kelvin)
T2=150°C = 150+273 = 423K
p2 =?
p1/T1= p2/T2
p2=p1xT2/T1
p2=1.0×105x423/273
= 1.54 x 105N/m2
The General Gas Equation from the Gas Laws
Identify the general gas equation from the gas laws
The three gas laws give the following equations:
- pV = constant(when T is kept constant)
- V/T = constant(when p is kept constant)
- P/T= constant(when V is kept constant)
These 3 equations are combined to give the ideal gas equation:
Where,
- p = the pressure of the gas
- V = the volume the gas occupies
- T = the gas temperature on the Kelvin scale
From
this equation we know that if a fix mass of gas has starting values of
p1, V1 and T1, and then some time later has value p2, V2 and T2, the
equation can be written as:
this equation we know that if a fix mass of gas has starting values of
p1, V1 and T1, and then some time later has value p2, V2 and T2, the
equation can be written as:
Exercise 1
Sabah
pumps up her front bicycle tyre to 1.7 x 105Pa. The volume of air in
the tyre at this pressure is 300 cm3. She takes her bike for a long ride
during which the temperature of the air in the tyre increases from 20°C
to 30°C. Calculate the new front tyre pressure assuming the tyre had no
leaks and so the volume remained constant?
pumps up her front bicycle tyre to 1.7 x 105Pa. The volume of air in
the tyre at this pressure is 300 cm3. She takes her bike for a long ride
during which the temperature of the air in the tyre increases from 20°C
to 30°C. Calculate the new front tyre pressure assuming the tyre had no
leaks and so the volume remained constant?
Absolute Scale of Temperature
Explain absolute scale of temperature
Absolute
zero is the lowest temperature that can be attained theoretically. It
is not possible to attain this temperature because all gases liquefy
before attaining it. The kelvin scale of temperature is obtained by
shifting the vertical axis to -273 degrees Celsius and renaming it 0 K.
On the scale 0 degrees Celsius becomes 273 K and 100 degrees Celsius
corresponds with 373 K.
zero is the lowest temperature that can be attained theoretically. It
is not possible to attain this temperature because all gases liquefy
before attaining it. The kelvin scale of temperature is obtained by
shifting the vertical axis to -273 degrees Celsius and renaming it 0 K.
On the scale 0 degrees Celsius becomes 273 K and 100 degrees Celsius
corresponds with 373 K.
Convertion of Temperature in Degrees Centigrade (Celsius) to Kelvin
Convert temperature in degrees centigrade (celsius) to kelvin
The
Kelvin temperature scale takes its name after Lord Kelvin who developed
it in the mid 1800s. It takes absolute zero as the starting point and
temperature measurements are given the symbol K (which stands for
“Kelvin”). Temperature differences on the Kelvin scale are no different
to those on the Celsius (°C) scale. The two scales differ in their
starting points. Thus, 0°C is 273K.
Kelvin temperature scale takes its name after Lord Kelvin who developed
it in the mid 1800s. It takes absolute zero as the starting point and
temperature measurements are given the symbol K (which stands for
“Kelvin”). Temperature differences on the Kelvin scale are no different
to those on the Celsius (°C) scale. The two scales differ in their
starting points. Thus, 0°C is 273K.
Converting from Celsius to Kelvin
- Temperature in °C + 273 = Temperature in K
Converting from Kelvin to Celsius
- Temperature in K – 273 = Temperature in °C
Example 5
The temperature of a gas is 65 degrees Celsius. Change it to the kelvin scale.
Solution
T(K) = degrees Celsius + 273, T(K) = 65+273
therefore T(K) = 338 K.
Standard Temperature and Pressure (S.T.P)
Explain standard temperature and pressure (S.T.P)
The
standard temperature and pressure (S.T.P) is a set of conditions for
experimental measurements to enable comparisons to be made between sets
of data. The standard temperature is 0 degrees Celsius (273 K) while the
standard pressure is 1 atmosphere (101300 Pa or 760 mm of mercury).
standard temperature and pressure (S.T.P) is a set of conditions for
experimental measurements to enable comparisons to be made between sets
of data. The standard temperature is 0 degrees Celsius (273 K) while the
standard pressure is 1 atmosphere (101300 Pa or 760 mm of mercury).
Expansion of Gas in Daily Life
Apply expansion of gas in daily life
Land
and sea breezes are the result of expansion of air caused by unequal
heating and cooling of adjacent land and sea surfaces. The piston engine
and firing bullets from guns work under principles of expansion of
gases.
and sea breezes are the result of expansion of air caused by unequal
heating and cooling of adjacent land and sea surfaces. The piston engine
and firing bullets from guns work under principles of expansion of
gases.
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