The formula for expansion of solids
You can work out the amount that a solid expands when its temperature is raised by a certain amount by using the following formula:
Expansion = original length x rise in temperature x linear expansivity
The
linear expansivity is a constant for a material and is how much a unit length of the material
would expand for a 1
o rise in temperature — it is a very small number: 0.000 0012 for
iron.
This means that a 1 m length of iron would expand by 0.000 0012 m when its
temperature is raised by 1
o C.
Example problems
Find the increase in the length of an iron girder 100 m long when the temperature is raised by 40oC.
Expansion 100 x 0.0000012 x 40 = 0.048 m = 4.8 cm.
Remember that it is the CHANGE in temperature that is important
Questions
1. Draw two diagrams to show what happens to the same bimetallic strip when it is:
(a) heated in a flame
(b) cooled in a freezer
2. What happens to the hole in a metal washer when the washer is heated? Does the hole get bigger, smaller or stay the same size?
3. Why will a hot, thick glass beaker shatter if plunged into cold water?
4. How will the expansion of the pendulum affect the running of a grandfather clock with a metal pendulum?
