7th Class Science Heat Thermal Expansion and Application

Thermal Expansion and Application

Category : 7th Class

*       Thermal Expansion and application


Thermal expansion is defined as the physical change in unit length, at per degree temperature. Coefficient of thermal expansion of the material is defined as, the degree of expansion divided by the change in temperature at constant pressure. Thermal expansion of a body depends on the applied temperature. If applied temperature is increased then it causes the thermal expansion of the body. Decreased temperature causes the contraction. In the general case of volumetric thermal coefficient of solid, liquid and gas is expressed as,

Volumetric change

 Change in temperature

 Actual volume of the material

 At constant pressure

 Volumetric coefficient of thermal expansion  


Pressure does not have affect on solid and liquid. But in the case of gas, pressure plays a very important role and coefficient of thermal expansion will vary, if pressure varies.

Coefficient of thermal expansion (Linear expansion) in a solid depends on the applied temperature. Pressure on a solid object does not cause change inside the object. Therefore in the case of solid, applied pressure is assumed to be negligible.

 Pressure is negligible

  Thermal coefficient in the area of a solid

Coefficient of thermal expansion of a liquid is calculated by its coefficient of thermal expansion in solid state and in gaseous state where, p»3a. Coefficient of thermal expansion in gases is volumetric expansion. Volume of the gases at constant pressure will increase if temperature increases and vice versa.

Volumetric thermal

V = Actual volume

P = At constant pressure

The object whose shape and size changes due to applied temperature can be used for some applications, like preparing thermometer. Thermal expansion can be seen in thermometer. The principle at which the application of thermal expansion works is defined as the expansion of materials at increasing temperature.      





       Gas expands with the application of heat. Which kind of expansion is noticed during the thermal expansion of the gases?

(a) Linear expansion

(b) Volumetric expansion

(c) Isotopic expansion

(d) All of these

(e) None of these


Answer: (b)



         The thermal expansion of a solid is the linear expansion. Which one of the following should be increased for increasing the thermal expansion?

(a) Light

(b) Sound

(c) Heat

(d) All of these

(e) None of these


Answer: (c)

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