## January 27, 2014

### Junior Inter Physics Imp Questions - Thermal Properties of Matter

Q: Can a substance contract on heating? Give an example.
A: Yes. Substance will contract on heating.
Eg: Leather, cast iron, rubber.

Q: Why gaps are left between rails on a railway track?
A: To compensate expansion of rails during summer, a gap is left between ends of two successive rails.

Q: Why do liquids have no linear and areal expansion?
A: Liquids have only volume expansion. They do not have their own shape, they occupy the shape of the container. Hence they do not have linear and areal expansions.

Q: What is specific gas constant? Is it same for all gases?
A: Universal gas constant per unit mass is called specific gas constant 'r'. It's value changes from gas to gas.

Q: Why utensils are coated black? Why the bottom of utensils are made of copper?
A: Since black bodies are good absorbers of heat, so lower portion of utensil is coated black. Copper is a good conductor of heat. It promotes the distribution of heat over the bottom of the vessel for uniform cooking.

Q: What is green house effect? Explain global warming.
A: Green House Effect: It is a process by which thermal radiation from earth's surface is absorbed by atmospheric gases (CO2, methane, nitrous oxide) and is re-radiated in all directions. The part of this re-radiation is
back towards the surface which results in heating up of earth's surface and atmosphere.

Global Warming: Concentration of green house gases enhanced due to human activities making earth warmer which cause problems for human life, plants and animals.

Q: Roof of buildings are often painted white during summer. Why?
A: White colour is a good reflector of heat. Good reflector is a bad absorber of heat. So, buildings are kept cool during summer.