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Thermal expansion of solids, liquids and gases Thermal Properties
Thermal expansion of solids, liquids and gases • Describe qualitatively the thermal expansion of solids, liquids and gases ◦ Show an appreciation of the relative order of magnitude of the expansion of solids, liquids and gases • Identify and explain some of the everyday applications and consequences of thermal expansion • Describe qualitatively the effect of a change of temperature on the volume of a gas at constant pressure Matter in general expands when heated. This can be explained using the molecular model of matter. When a solid is heated, its molecules vibrate faster about their fixed positions. As a result of this, the molecules move slightly further apart than when they are cold. The cumulative effect of all the molecules result in the volume expansion of the solid.
Solid expansion The expansion of a solid when heated is small. A metre rule may expands by 1 – 2 mm when heated. Through small, this expansion can create a very large force if it is restrained. Railway tracks expand during a hot day. If the tracks are not designed for the expansion, the entire track may bend out of shape during expansion. However, the expansion of solid may also be put into good use. Two pieces of different metals with different expansion coefficients may be bound together. When temperature changes, the two metals expands differently. This causes the strip to bend according to the temperature. This bimetallic strip may be used to open and close an electric circuit to control temperature.
Liquid expansion Liquid also expands for the same reason. However, since liquid particles are usually less tightly bound to each other molecules, they generally move further than solid particles when heated. Hence, liquid expands more than solid if the temperature rise is the same. This expansion of liquid may be used in a liquid-in-glass thermometer. The volume increase of alcohol or mercury may be calibrated to provide a temperature reading since the expansion is almost directly proportional to the temperature rise.
Gas expansion • Gases behave differently from solids and liquids. • Gas molecules are far apart and weakly attracted to each other. • Heat causes the molecules to move faster and the volume increases much more than solids and liquids. • However, gas do not have to expands when heated. • If the gas is confined to a fixed volume, the increase in temperature may cause the pressure to increase if the volume of kept constant. • If the gas is allowed to expand, the pressure may be kept constant. We may use the kinetic model to explain this. When a gas is heated, the molecules move faster. The higher speed of molecules result in a higher frequency of collision with the container walls. These collisions are also harder as the molecules are faster. Together, these cause the pressure to increase. As the pressure is higher than original value, the gas will push the piston out. This result in a volume increase. As the volume is now larger, the frequency of collisions with the container walls is less and the pressure decrease. The volume stops expanding when the internal pressure equals to the original external pressure.
This is expansion of gas under constant pressure. Feb 19, 2012 • • • •
Posted by admin 2 comments IGCSE Physics Bimetallic Strip, Cumulative Effect, Everyday Applications, Expansion Coefficients, Expansion Of Solids, Glass Thermometer, Hot Day, Liquid Expansion, Liquid Particles, Liquids And Gases, Molecular Model, Molecules, Order Of Magnitude, Solids Liquids And Gases, Temperature Reading, Temperature Rise, Thermal Expansion Of Solids, Two Pieces, Volume Expansion, Volume Increase
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muzaffar mehdi (Oct 01, 2013) i love it, it helped me to do my school work thats coooooooooool
krishanand (Apr 18, 2016) excellent
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