- What do you see in these pictures?
- What is meant be expansion?
Is the difference between the original size of an object and its size when its cooled or heated.
- Why things expand?
When a solid is heated its particles
vibrate more rapidly. As a result they collide and push each other
further apart. |
|
-
- Explain what happen when solids are heated?
When a solid is heated, its molecules gain kinetic energy and
vibrate more vigorously. As the vibration become larger, the molecules
are pushed further apart and the solid expands slightly in all directions.
- Explain what happen when solids are cooled?
When a solid is cooled, its molecules lose kinetic energy and
have less vibration. As the vibration become lower, the molecules are
pulled closer and the solid contracts slightly in all directions.
- List the factors which affect the expansion of
solids?
Original length (direct), temperature (direct), material type
- Compare between the expansivity of solids,
liquids, and gases.
Solids in general have the smallest expansivity while gases have
the greatest expansivity and liquids lie in between.
- List four real-life
problems due to expansion of materials.
| On a hot day concrete runway sections in airport expands and
this cause cracking. To solve this
problem we leave small gabs between sections. |
|
|
| On a hot day concrete bridges expand. To
solve this problem, we leave small gab at one end and support the
other end with rollers. |
|
|
| Telephone wire contract on cold days. To
solve this problem, we leave wires slack so that they are free to
change length. |
|
|
| On a hot day railway lines expand. To
solve this problem, gaps are left between sections of railway
lines to avoid damage of the rails as the expand in hot weather. |
|
|
- What us meant by bimetal
strip?
A bimetal strip is a two-thin strips of different metals welded
together.
- Describe the action of a bimetal?
When the bimetal strip is heated, the brass expands more than invar
and this makes the strip bends with brass on the outside of the
curve.
If the strip is cooled, instead of heated, it would bend the
opposite way.
|
|
- Explain how to build a fire alarm using bimetals.
- What is meant by a thermostat?
A thermostat is temperature operated electrical switch that uses
the expansion properties of a bimetal strip.
- Explain the structure and the action
of thermostat?
The figure shown to the right shows a
thermostat. The control knob sets the temperature at which the
switch will turn off. The bimetal strip provides the expansion
and contraction which results closing or opening the electrical
circuit of the system under control.
When the bimetal strip is heated it curves and breaks contact then
the temperature reaches a certain value. Thus, switching off the
current to the system under control. |
|
- List some applications to thermostat in industry
- electric irons
- fish tanks
- home heating/cooling systems
- Ovens, refrigerators,
- fire alarms, car flashers
|
|
-
- What do you see in the picture below?
- Explain what happen when liquids are heated?
When a liquid is heated, its molecules gain kinetic energy and
vibrate more vigorously. As the vibration become larger, the molecules
are pushed further apart and the liquid expands slightly in all directions.
- Explain what happen when liquids are
cooled?
When a solid is cooled, its molecules lose kinetic energy and
have less vibration. As the vibration become lower, the molecules are
pulled closer and the solid contracts slightly in all directions.
- List the factors which affect the expansion of
liquids?
temperature (direct), liquid volume (direct), liquid type
- Compare between the expansivity of liquids and solids?
Expansivity of liquids is much greater than the expansivity of solids.
- Explain why when heating a liquid, its level initially decreases and then it increases to become more larger than the original level?
The liquid level drops due to the expansion of its container which initially absorbed all the heat. After a while, the heat reaches the liquid it compensates for the expansion of the container and rises much more than the original level.
- List some applications that uses the expansion of liquids?
- Thermometers
- The valve shown below operates based on the expansion of the oil. As the room warms of the oil in the valve expands and pushes the piston down. This shuts off the flow of hot water. When the temperature drops the valve opens again.
- Explain the effect temperature on volume of water?
The water volume decreases from 0ºC-4ºC. After 4ºC, the volume of water increases gradually.
- When water has its minimum volume or higher density?
Water has its minimum volume at 4ºC.
- Explain the effect temperature on density of water?
The water density increases from 0ºC to 4ºC. After 4ºC, the density of water decreases gradually.
- Explain why filled bottles of water when placed in a freezer may burst when water is frozen?
When water freezes it changes to ice and its volume increases by about 9%. Since bottle is filled, then there is no space left for the increased 9%, thus a high pressure starts to builds up against the bottle walls from inside. This high pressure burst the bottle.
- Explain why ice floats on water?
When water freezes it changes to ice and its volume increases by about 9%. The increase in volume means that the ice is less dense than water beneath it and it will floats.
- Explain why the surface of a lake freezes while the deepest water stays at 4C?
-
- Compare the expansion of gases to that of solids and liquids?
The expansion of gases is much more larger than that of solids or liquids under the same rise in temperature.
- Explain the effect of temperature on gas volume when pressure is constant?
When pressure is constant, the volume of a gas is directly proportional to the Kelvin temperature (Charlie's Law).
When the temperature of a gas is increased, the molecules move faster and the collisions become more violent thus they spread away from each other causing the volume to increase.
- Explain the effect of temperature on gas pressure when volume is constant?
When volume is constant, the pressure of a gas is directly proportional to the Kelvin temperature (Pressure Law).
In gas, molecules are always on the move. They travel fast, hitting each other and the sides of their container. If the temperature is increased, the molecules move faster and the collisions become more violent thus the pressure increase.
|
|
- Explain an experiment to show the study the effect of temperature on gas pressure?
- What is the statement of "Charlie's law"?
When pressure is constant, the volume of a gas is directly proportional to the Kelvin temperature.
Mathematically: V1/T1=V2/T2
- What is the statement of the pressure law?
When volume is constant, the pressure of a gas is directly proportional to the Kelvin temperature.
Mathematically: T1/P1=T2/P2
- What is the statement of the Boyle's law?
When temperature is constant, the volume of a fixed max of a gas is inversely proportional to the pressure
Mathematically: P1V1=P2V2
- What is the general law of gases?
When gas parameters change from P1,V1, and T1 to P2, V2, T2 then P1V1/T1=P2V2/T2
|