CHAPTER 9
TRANSFER OF HEAT NATURE
EXERCISE
Q. 1. State whether True or False.
(a) In solids, heat is transferred mainly through the process of convection. [T/F]
Ans. False
(b) Air gets heated by the process of convection. [T/F]
Ans. True
(c) Radiation is a method of heat transfer that requires a medium. [T/F]
Ans. False
(d) Water seeps through clay faster than through gravel. [T/F]
Ans. False
(e) A sea breeze is the movement of cooler air from the sea towards the land during the day. [T/F]
Ans. True
Q. 2. Darken the circle of the correct answer.
(i) A hot metal pan is removed from a flame and placed on a pan counter. It eventually cools down to room temperature. How does it primarily lose its heat?
(a) Through convection.
(b) Through conduction.
(c) Through radiation.
(d) Through a combination of conduction and convection.
Ans. (c)
(ii) What is the primary reason why water seeps much more slowly through clay than through gravel?
(a) Clay is found deeper underground than gravel.
(b) Gravel particles are smaller and remain packed together more tightly.
(c) The spaces between clay particles are much smaller and loosely bound.
(d) The chemical composition of clay repels water.
Ans. (c)
(iii) Which of the following processes primarily transfer heat through a solid metal rod and water?
(a) Radiation and convection
(b) Conduction and convection
(c) Convection and radiation
(d) Radiation and conduction
Ans. (b)
(iv) A pressure cooker is made of steel or aluminium, while its handle is made of plastic or wood. Why are different materials used?
(a) Steel or aluminium is a poor conductor of heat, and plastic is a good conductor.
(b) Steel or aluminium is a good conductor of heat, and plastic is a poor conductor.
(c) Steel or aluminium transfers heat by convection, while plastic transfers heat by conduction.
(d) Steel or aluminium transfers heat by conduction, while plastic transfers heat by convection.
Ans. (b)
Q. 3. Read the following two statements carefully. One of them is given as the ‘Assertion’ and the other as the ‘Reason’.
Assertion: Sea breeze blows from the sea toward the land during day time.
Reason: Land gets heated up faster than water under sunlight, so warm air over land rises and is replaced by cooler air from the sea.
Choose the correct answer from the available options:
(a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
(c) Assertion is true, but Reason is false.
(d) Assertion is false, but Reason is true.
Ans. (a).
Q. 4. Fill up the blanks.
(a) The process of heat transfer from the hotter part of an object to a colder part without changing the position of its particles is called _________.
Ans. conduction
(b) Materials that do not allow heat to pass through them easily are called _________ of heat.
Ans. poor conductor
(c) In liquids and gases, heat is transferred mainly by the process of _________.
Ans. convection
(d) All kind of objects exchange heat with their surroundings through the process of _________.
Ans. radiation
Q. 5.
A stainless-steel spoon kept in a cup of hot water becomes hot within a few minutes. Explain how heat is transferred along the spoon and predict which part becomes hot first and which part gets heated up last?
Ans. Heat travels through the spoon by the process of conduction because steel is a good conductor of heat. The heat passes from the hot water to the spoon and then spreads throughout it.
The end of the spoon dipped in hot water becomes hot first, while the handle or the farthest end of the spoon becomes hot last.
Q. 7.
On sunny days in coastal areas, houses often have windows open facing towards the sea. Explain how this design helps keep the indoors comfortable, with reference to the mechanism of sea breeze.
Ans. During daytime, land gets heated more quickly than sea water. As a result, the air above the land becomes hot and rises upward. Cooler air from the sea then moves towards the land to occupy the empty space. This cool air coming from the sea is known as sea breeze. Therefore, windows facing the sea are kept open so that the cool sea breeze can enter the house and keep the indoors comfortable.
Q. 8.
People sitting around a fireplace feel warm even if the air between them is cool. Explain the actual mode of heat transfer involved in this process.
Ans. The mode of heat transfer involved in this process is radiation. In this process heat is transferred from an object to the other without any medium.
Q. 9.
List the major causes of groundwater depletion, highlighting the specific factors in rural, urban, and industrial areas.
Ans.
(a) Causes of groundwater depletion in rural areas
(i) Cultivation of high water demanding crops.
(ii) Wastage of water by inefficient irrigation system.
(b) Causes of groundwater depletion in urban areas
(i) Over-extraction of groundwater by a large population for daily consumption and industrial use.
(ii) Loss of vegetation cover and wetlands.
(iii) Reduced infiltration of rainwater due to structures made of concrete.
(c) Causes of groundwater depletion in industrial areas
(i) Excessive and unregulated extraction of groundwater for use in various industrial processes.
(ii) Pollution of groundwater by industrial effluents.
Q. 10.
Two identical cups are filled with equally hot tea—one porcelain and one stainless steel. Predict which cup of tea will remain hot for a longer time, and explain the reason.
Ans. The porcelain cup will remain hot for a longer time. Because porcelain is a poor conductor of heat and hence it does not allow heat from the tea to pass through it. On the other hand, stainless steel is a good conductor of heat and it allows heat from the tea to pass through it. Then the heat is radiated from its surface.
Q. 11.
The temperatures of three substances were recorded after being heated to the same temperature and then allowed to cool under the same conditions. The data are shown below:
| S.I. No. | Time (minutes) | Temperature of Substance A (°C) | Temperature of Substance B (°C) | Temperature of Substance C (°C) |
|---|---|---|---|---|
| 1 | 0 | 80 | 80 | 80 |
| 2 | 10 | 72 | 65 | 55 |
| 3 | 20 | 66 | 58 | 40 |
| 4 | 40 | 62 | 46 | 32 |
Answer the following:
(a) Which substance cools fastest?
Ans. Substance C
(b) Which substance retains heat for the longest time?
Ans. Substance A
(c) Based on the above data, which substance would you prefer to use for making a tea cup?
Ans. Substance A
Q. 12.
A hot water bag gradually cools down after being used for some time. Through which process does it lose heat? Explain.
Ans. A hot water bag mainly loses heat through conduction. Heat passes from the hot water to the rubber bag and then from the bag to the body by direct contact. Some heat is also lost to the surroundings through radiation.
Q. 13.
Explain why do thin blankets used together provide more warmth in winter than a single thick blanket?
Ans. Two thin blankets trap a layer of air between them. Since air is a poor conductor of heat, it prevents heat from escaping from our body to the surroundings. Therefore, two thin blankets together give more warmth than a single thick blanket.
Q. 14.
Why is it advised to paint the outer walls of buildings white in hot regions?
Ans. White colour reflects most of the heat falling on it and absorbs very little heat. As a result, buildings painted white remain cooler in hot regions during summer.
OLD Question Answer
Transport systems of animals and plants
Exercise
1) Match the 1st pillar to the 2nd pillar
Pillar-1 Pillar-2
i) Leaves a) Absorption of water
i ) Xylem b) Transfusion
i i i) Chili Shipa d) Water transport
iv) Flame e) Carbohydrate synthesis
2) Fill in the blanks.
i) Radiation is transported to different parts of the body after the heart by ________.
Answer: Arteries
ii) Hemoglobin is carried in ________ cells.
Answer: Red blood cells.
i i i) Arteries and veins are connected by ___________ reticulum.
Answer: FOR STUDENTS
iv) Coordinated expansion and contraction of the heart is called __________.
Ans: The pulse is spoken.
v) The main excluded substance in humans is _______.
Answer: Writing.
v i) Sweat contains water and ________.
Answer: There is urea.
vii) Julia’s condition The excretory fluid removed from the kidney is called ________.
Answer: Birth.
viii) The upward movement of water through suction is due to ________.
Answer: Sensation.
3) Leave the correct answer.
a) Water transport in plants,
i) Xylem ii) Phloem iii) Pores iv) Cells
Answer: – Xylem.
b) Absorption of water by plants can be increased if plants are kept-
i) Canopy ii) Low consumption iii) Under foam
iv) Polythene monolayer covered bags
Answer: – Cut off.
4) Explain the need for transportation of plant or animal material.
Answer: FOR STUDENTS
5) If Tejat Anuchakrikika Nathake Tetia what will be written?
Ans:- If Tejat Anuchakrikika is kept, then Tej Khamala is not closed.
6) What is literature? Mention two functions of Patrandhra .
Ans: – Leafy and porous leaves.
1) Leaves remove carbon dioxide from the atmosphere.2) Sensation is carried out in the plant through leaf pores.
7) Sensation is the essential function of plants? Explain?
Ans:- Plants absorb mineral nutrients and water through soil. All those plants that absorb water from the soil do not use it. Water evaporates through the pores on the surface of the pot through the process of transpiration. As a result of the evaporation of water from the leaves, absorption forces are created inside the xylem tubes. With which the oak tree can transport water to a great height. The plant is also cooling to the senses.
8) What are the components of radiation?
Ans:- The components of blood are – plasma, red blood cells, white blood cells, and platelets.
9) What is the need for radiation in all parts of the body?
Ans: – Radiation to all parts of the body For this reason, the digested food particles are transported to different parts of the body through the small intestine. After breathing, oxygen is absorbed by the body’s cells and the body removes unnecessary substances from the body.
10) What gives color to radiation?
Ans: – Hemoglobin gives light color.
11) Describe the function of heart?
Ans: – It is the organ which beats continuously and carries out the work of the Niyat pump by drawing in other substances with the help of the heart.
12) What is the need for Uliai Diato after the body is excluded?
Ans:- Excluded substances are toxic and need to be washed by the body.
13) Human Drawing Techniques Now draw a picture and identify its different parts.
Answer:- You will do this work yourself.
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