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Thermal Expansion Examples
Give Reasons for the following
1. Gaps are left in between rails while laying a railway track.
During summer season the rails made of iron expand due to hot sunshine. The ends of the rails come closer and they may hit each other. To .avoid this, expansion gaps are left between the ends of rails.
2. Gaps are left in between two joints of a concrete bridge.
The concrete slabs expand during hot summer. Their edges may hit each other and cause dislocation. To prevent this gaps are left in between two joints of a concrete bridge
Cracking of a thick glass tumbler
Glass is a poor conductor of heat. When hot liquid is poured into the tumbler, the inner surface of the tumbler becomes hot and expands while the outer surface remains at the room temperature and does not expand. Due to this unequal expansion, the tumbler cracks.
Electric wires between electric posts contract on cold days and sag in summers. To solve this problem, we leave wires slack so that they are free to change length.
Glassware used in kitchen and laboratory are generally made up of Borosilicate glass (pyrex glass). The reason is that the Borosilicate glass do not expand much on being heated and therefore they do not crack.
* The photographs below show an expansion joint at the end of a bridge in winter and in summer. Which season is shown in each picture? Explain how do you know?
A. Photograph A is taken in winter. As the climate is cool, the edges contract. So there is a wide gap.
B. Photograph B is taken in summer. As the climate is hot the edges expand. So the gap becomes small.
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