EVENTS CONVENT HIGH SCHOOL
01/02/2022 CLASS- 7 SESSION 2021-22
SUBJECT : SCIENCE
CHAPTER-4
HEAT
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Q.1.Fill in the blanks
(a) The hotness of an object is detetmined by its ____________ .
(b) Temperature of boiling water cannot be measured by a ____________ thermometer.
(c) Temperature is measured in degree ____________ .
(d) No medium is required for transfer of heat by the process of ____________.
(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ____________
(f) Clothes of ___________ colours absorb heat better than clothes of light colours.
Ans. (a) temperature (b) clinical (c) Celsius (d) radiation (e) conduction (f) dark
Very Short Answer Type
Question 1.In a mercury thermometer, the level of mercury rises when its bulb comes in contact with a hot object. What is the reason for this rise in the level of mercury?
Answer:
As the temperature increases, then expansion in mercury takes place which leads to the rise in the level of mercury in thermometer.
Question 2.Shopkeepers selling ice blocks usually cover them with jute sacks. Explain why.
Answer:As we know that jute sacks is thermal insulators, it helps ice not to be melt immediately. So, shopkeepers used to cover ice blocks with jute sacks.
Question 3.The radiators in cars are painted black. Explain why.
Answer:Since, the black bodies are better radiators, so due to this reason, radiators in cars are painted black.
Question 4.To keep her soup warm, Paheli wrapped the container in which it was kept with a woollen clothes. Can she apply the same method to keep a glass of cold drink cool? Give reason for your Answer:
Answer:
Yes, she can apply the same method to keep a glass of cold drink cool because wool is a thermal insulator, and it cannot allow to heat pass through it.
Short Answer Type
Question 1.The handle of a pressure cooker is covered with the thick plastic. Explain why?
Answer:
As we know that plastic is a bad conductor of heat due to which the heat from the cooker does not flow to its handle and we can hold it easily.
So, this is a reason because of which the handle of a pressure cooker is covered with the thick plastic.
Question 2.Differentiate between two modes of transfer of heat, i.e. convection and conduction?
Answer:
Difference between convection and conduction
| Conduction | Convection |
| The mode of transfer of heat from the hotter part material to its colder part or from a hot material to a cold material in contact with it without the movement of material as a whole. So, this phenomenon is known as conduction | The mode of transfer of heat from the hotter part of a fluid to its colder parts by the movement of liquid itself. So, this phenomenon is known as convection. |
| In all the solids, heat is transferred by the process of conduction | In all the liquids and gases, heat is transferred by the process of convection |
Question 3.Describe the effects of heat?
Answer:
The effects of heat are
(i) When an object is heated, then it becomes hotter and may get expand. So, in this heat may change the state of the body like ice can also get change into the water.
(ii) Heat sometimes acts as a catalyst to speed up the chemical reaction.
(iii) Heat can even kill the bacteria as well.
Question 4.The freezer is located at the top of the refrigerator. Explain why?
Answer:
The freezer is located at the top of the refrigerator. It is because the air inside and around the compartments of freezer gets cool and move downwards and on the other side, the lesser cool air moves upward to get cooled.
So, as a result of this, convection of heat are setup in the air and the tower section of the . refrigerator also gets cooled faster. .
