Long Answer Questions:
1. Write about the different modes of heat transfer.
2. Write two applications of heat radiations.
3. What is thermometer? Write its types.
4. Give an activity to show that liquids transfer heat by the process of convection.
5. Draw a labelled diagram of a clinical thermometer.
6. Explain with the help of an activity that black surfaces are better absorbers of heat.
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Answers
Answer:
1.Heat transfer takes place by the process of radiation when there are no particles of any kind which can move and transfer heat. So, in an empty space or vacuum heat is transferred by radiation. We shall now study heat transfer by conduction, convection, and radiation in detail.
2.A good example would be heating a tin can of water using a Bunsen burner. Initially the flame produces radiation which heats the tin can. The tinj can then transfers heat to the water through conduction. The hot water then rises to the top, in the convection process.
3.A thermometer is a device that is used to measure the temperature of a body. Common types of thermometers are Medical thermometers, Infrared thermometers, Mercury thermometers, thermocouple thermometers, laboratory thermometers, Bimetallic strip thermometers, Pyrometers, etc.
4.You need two glasses, some colour, hot and cold water. Take hot water in a glass and add some colour to it. Take cold water in another glass and place the CD on this glass as a lid.
6.A black object absorbs all wavelengths of light and reflects none and that's why it appears black. Consequently, black absorbs the most heat. Objects that are white, on the other hand, reflect all wavelengths of light and that's why they appear white to us, therefore absorb the least heat.