NCERT Class 7 Science Chapter 4 | Heat | Expected Questions
Expected questions from NCERT Class 7 Science Chapter 4 Heat are given below.
Fill in the blanks.
1. In winter we wear ……………………….. clothes. (woollen / cotton)
2. In summer we wear, ………………………. clothes. (woollen / cotton)
3. Woollen clothes are obtained from ……………………….. (plant / animal) fibres.
4. Cotton clothes are obtained from ……………………….. (plant / animal) fibres
1. woollen; 2. Cotton; 3. Animal; 4. Plant
5. …………………….. is the measure of the hotness of an object
6. Which device is used to measure temperature?
7. What is a clinical thermometer?
Clinical thermometer is the device used to measure our body temperature.
8. Write a short note on clinical thermometer.
A clinical thermometer is a device used to measure body temperature. It consists of a long, narrow and uniform glass tube. At one end of this glass tube, there is a bulb containing mercury. You can also find a small, shining thread of mercury outside the bulb. There is a scale on the thermometer and it measures temperature in degree Celsius. A clinical thermometer can measure temperature from 350 C to 420 C.
9. What is the normal temperature of human body?
10. Why does a clinical thermometer has a range between 350C and 420C?
The clinical thermometer is only used to measure human body temperature. The temperature of the human body does not normally go below 350C or above 420C. Hence, this thermometer can only measure temperature in between these limits.
11. What is a maximum-minimum thermometer?
A maximum-minimum thermometer is used to measure the maximum and minimum temperature of the previous day shown in whether reports.
12. What is the range of a typical laboratory thermometer?
A typical laboratory thermometer has a range between -100C and 1100C.
13. What are the main differences between clinical and laboratory thermometers?
The clinical thermometer is used to measure the temperature of the human body whereas the laboratory thermometer is used to measure the temperature of other objects. The clinical thermometer has a range between 350 C and 420 C whereas a laboratory thermometer can measure between -100C and 1100C. While taking the temperature, the laboratory thermometer should be kept upright and not tilted. Also, the reading should be taken while the thermometer is still in contact with the liquid or other substance whose temperature is to be measured. This is because in the case of a laboratory thermometer, the mercury tends to fall as soon it loses contact with the object whose temperature is taken. A clinical thermometer has a kink near the bulb to prevent the mercury from falling on its own. And hence, its reading does not change even after it is removed from the object whose temperature is measured.
15. Heat flows from a ………………….. object to a …………………… object.
Hotter object to a colder object
16. What is conduction?
Conduction is the process by which heat is transferred from the hotter end to the colder end of an object.
17. Name the process responsible for the transfer of heat in solids
18. What are conductors of heat?
Materials which allow heat to pass through them easily are good conductors of heat. Examples are: iron, copper, aluminium
19. What are insulators?
Insulators are materials which do not allow heat to easily pass through them. They are bad conductors of heat. Examples are: plastic and wood.
20. Explain how heat is transferred in water with the help of an activity
Fill two-thirds of a beaker or flask with water. Place it on a tripod and then put a candle below the beaker/flask. Once the water in the beaker is still, place a crystal of potassium permanganate at the bottom of the beaker gently with a straw. The candle should be placed just below the crystal. When the candle is lit, the water near the flame will become hot first. This hot water will move up and then the cold water from the sides will move down to occupy its space. When this water also becomes hot, it will move up and water from the sides will move down towards the heat source again. This process continues till the whole water becomes hot. This mode of heat transfer is known as convection.
21. What is sea breeze?
Land gets heated faster than water. Hence, during the day, air over the land in coastal areas becomes hotter than the air over the water. This hot air will move up and then cooler air from the sea will rush in to take up its space. Meanwhile the warm air from the land will move towards the sea. This cool air from the sea is called sea breeze.
22. What is land breeze?
At night, the land cools down faster than the water. Consequently, cool air from the land will move towards sea at night. This is called the land breeze.
23. What is radiation?
Radiation is the process by which sun’s heat reaches earth. No medium is required to transfer heat by radiation.
24. Why do we wear light colored clothes in summer?
Light coloured clothes reflect most of the heat that falls on them and hence they keep us cool in summer.
25. Why do we wear dark colored clothes in winter?
Dark colored clothes absorb more heat than light colored clothes and hence they keep us warm in winter.
26. How do woollen clothes keep us warm in winter?
Wool is a poor conductor of heat and there is air trapped between the wool fibres. This air prevents the flow of heat from our body to the cold surroundings. This way they keep us warm.