Class 7 Basic Science Chapter 6 Question Answer Notes Heat in Everyday Life

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Heat in Everyday Life Class 7 Questions and Answers Notes

Class 7 Basic Science Chapter 6 Heat in Everyday Life Question Answer Pdf

Basic Science Class 7 Chapter 6 Question Answer Kerala Syllabus

Let Us Assess

Question 1.
Consider some situations in everyday life.

• Tightly bound electric wires get sagged in summer.
• One end of a PVC pipe is heated and the end of another pipe of the same diameter is inserted into it to join them.

a. Which property of matter with respect to heat is evident in the above two cases?
b. Based on this, can you explain why a fully inflated balloon bursts when exposed to sunlight?

Answer:
a. Thermal Expansion
When it gets hot, the metal wires expand and become longer, causing them to sag.

b. Thermal Expansion
A fully inflated balloon bursts in sunlight because the heat causes the air inside to expand. This increased pressure can stretch the balloon beyond its limit, leading to a burst.

Question 2.
Observe the arrangement of an experiment shown in the picture.

An injection bottle fitted with a plastic tube is placed in a beaker of hot water. The tip of this tube is inserted into the hole at the bottom of another jar filled with water.
a. What do you observe?
b. What inference can be drawn from this?
Answer:
a. When the injection bottle is placed in hot water, the air inside the bottle heats up and expands. This causes the coloured water in the jar to be pushed up the tube.
b. Heating the air inside the bottle makes it expand, which pushes the water up the tube (Thermal expansion). This shows that warm air takes up more space.

Question 3.
Classify and tabulate the following materials on the basis of thermal conductivity.
Iron, Paper, Bakelite, Copper, Wood, Steel, Aluminium, Cloth.
Answer:
Good conductors: Copper, Aluminium, Iron, Steel
Poor conductors: Wood, Bakelite, Paper, Cloth

Question 4.
Haven’t you noticed the utensils used for cooking? What is the difference between the materials used to make the utensil and its handles? Explain this on the basis of thermal conductivity.
Answer:
Materials for Utensils: Metals have high thermal conductivity, which means they heat up quickly and efficiently transfer heat to the food being cooked.
Materials for Handles: Plastic and wood have low thermal conductivity, meaning they do not conduct heat well. This keeps the handles cooler and safer to touch, preventing bums when cooking.

Question 5.
Hot tea of same quantity is kept in an open steel tumbler and in a closed glass tumbler of same size. Tea in which tumbler stays hot longer? Explain your finding on the basis of heat transmission.
Answer:
The tea in the closed glass tumbler stays hot longer than in the open steel tumbler. Because in an open tumbler heat is lost quickly through convection and evaporation, cooling the tea. But in a closed tumbler, the lid keeps heat and steam inside thereby reducing heat loss.

Class 7 Basic Science Chapter 6 Extended Activities Answers

Question 1.
Dismantle a thermoflask with the help of elders. Examine whether it has the following mechanisms to prevent heat transmission.

Method of Heat transmission	Preventive mechanism
Conduction	Vessel made of poor conductor
Convection	Evacuated double wall
Radiation	Silver coated interior of double wall

Answer:
Hint: The following diagram helps to identify the parts of a thermoflask.

Class 7 Basic Science Chapter 6 Intext Question and Answers

Question 1.
Observe the picture. Which energy forms are utilized here?
Answer:
Light energy, Solar energy, Heat energy, Wind energy We make use of different forms of energy in our daily life.

Question 2.
What are the various situations where heat energy is used? List them.
Answer:
For cooking, Boiling water, Drying Clothes, Photosynthesis etc.
Many changes are caused by heat energy in different states of water.

Question 3.
Ice is the solid form of water. What happens when ice is exposed to air?
Answer:
When exposed to air, ice melts into water.

Question 4.
What happens when water is boiled?
Answer:
Water changes into water vapour.
Steam is the gaseous form of water. When substances are heated, they absorb heat energy.
Let’s do an experiment to understand that heat energy can change the state of matter.
Melting Ice Cubes

Materials required: 2 Glass tumblers, water at normal temperature, hot water, ice cubes.
Take water at normal temperature in one glass tumbler and hot water in another one as shown in the picture. Put some ice cubes in both glasses.

Question 5.
Ice cubes in which glass melts faster? Why?
Answer:
Glass with hot water. There is more energy in hot water. So ice can absorb energy from the hot water at a faster rate than cold water and melts faster.

Question 6.
Which form of energy caused the change of state of ice?
Answer:
Heat energy

Question 7.
Didn’t ice get adequate heat from water to melt?
Answer:
Yes

Question 8.
Have you noticed coconut oil solidifying during winter? What is the reason?
Answer:
Coconut oil is in liquid state. In winter the atmospheric temperature starts decreasing and starts cooling or losing heat, and changes to solid state.
Heat is a form of energy that can change the state of matter

Transfer of Heat
Observe the picture.

The picture shows a pot of rice being cooked on a gas stove.

Question 9.
How did the rice get the heat energy radiated from the flame of the gas stove?

Answer:
Rice gets cooked when the heat radiating from the flame of the stove is transferred through the pot ’ and water and reaches the rice.

Question 10.
What happens to the pot after turning off the gas stove for a while?
Answer:
Heat is transferred to the surroundings, not only from the pot but also from the substances inside it. This results in heat loss to the vessel and its contents.

Question 11.
Did all the pins fall down at the same time?
Answer:
No

Question 12.
Which pin had fallen first?
Answer:
The pin near the flame falls first.

Question 13.
What causes the pins near the flame to fall first and those farther away to fall later? Record your observations and inferences in the Science Diary.
Answer:
This is due to the transmission of heat from the flame through the Aluminum rod.
• Repeat this experiment with Copper and Iron rods.
Heat transmission occurs not only in Aluminium but in other metals like copper and iron rods. Heat is transmitted in metals by the transfer of heat energy.
• Repeat the experiment with a piece of wood and a glass rod.
Heat transmission does not occur in a glass rod and with a piece of wood.

Question 14.
In the following situations, do we use good conductors or poor conductors?
a. To remove a hot vessel from the stove
b. To make handles of cooking utensils
c. To make cooking utensils
Answer:
a. Poor conductors
b. Poor conductors
c. Good conductors

Question 15.
Both good conductors and poor conductors are used in the same vessel. Explain the reason for this.
Answer:
In a vessel, good conductors are used to efficiently transfer heat, while poor conductors are used to insulate or protect parts from heat. For example, in a cooking pot, the good conductor helps heat the food evenly, while the poor conductor on the handle prevents it from getting too hot to touch. This way, the vessel works better and is safer to use.

Question 16.
Find more examples of such vessels and present them in the class.
Answer:
Pressure cooker, Non-stick pan

Question 17.
Why do we put the fire right underneath the vessel while cooking? How about heating the sides of the vessel? What are your responses?
Answer:
Putting the fire underneath the vessel heats the bottom directly, which cooks the food quickly and evenly.

Let’s do an experiment

Materials required: A transparent plastic jar with a lid, a glass tumbler with the same diameter as that of the jar, mason pipe, Potassium permanganate, hot water, cold water. Make two holes in the lid of the plastic jar. Fix a 10 cm long mason pipe in each hole in an airtight manner. Take hot water in the glass tumbler having the same diameter as that of the plastic jar. Add some Potassium permanganate granules to it. Take some cold water in the plastic jar and close it with the lid fitted with the mason pipe. Place this plastic jar upside down over the glass tumbler filled with hot water containing Potassium permanganate.

Observation
The water in the plastic jar will start to turn purple. This happens because the purple colour from the hot water slowly moves up into the cold water.
• When hot water flows up through one mason pipe, cold water flows down through the other pipe. This cold water becomes hot and rises up again. Thus, heat spreads throughout the liquid.
• In this experiment, heat was transmitted from hot water to cold water by the displacement of molecules. Here the heat energy is transferred when molecules move across. Heat transmission occurs in all liquids by the displacement of molecules.

Question 18.
Can heat be transmitted without the help of a medium?
Answer:
Yes, heat can be transmitted without the help of a medium through a process called radiation. You know that the Earth gets heat mainly from the Sun. We also know that there is a vacuum area between the Sun and the Earth. This vaccum area is spread over 15 crore km. There is no medium between the Earth and the Sun. Therefore, heat cannot be transmitted by conduction or convection. The heat from the Sun reaches the Earth by a process called radiation.

Question 19.
Write down some situations where heat is transmitted by radiation.
Answer:

• Heat reaches down from a glowing filament bulb.
• Fireplace: The warmth from a fire radiates out and heats the room.
• Microwave Oven: Microwaves use electromagnetic radiation to heat food.

Question 20.
Which are the commonly used devices to reduce heat loss? List them.
Answer:
Thermoflask, casserole, thermal cooker

Question 21.
Find out the various situations in which ice boxes are used.
Answer:
Ice boxes help maintain the temperature of food and beverages, preserving freshness and ensuring safety during travel, camping trips, fishing etc

Question 22.
How does the ice box minimize all three types of heat loss?
Answer:
Conduction: Thick walls stop heat from coming through.
Convection: An airtight design prevents warm air from flowing around the ice cube.
Radiation: Reflective surfaces block heat rays.

Question 23.
Haven’t you seen the wires on the electric pole for distributing electricity? Why do these wires get sagged in summer?
Answer:
When it’s hot outside, the temperature rises, and so do the temperatures of the wires. Most electric wires are made of metals like aluminium or copper, which expand when they get hot. This means the wires get longer and, as a result, they sag more.

Question 24.
Let’s find out the reason by analysing the following situations.
a. A very tight pen cap is removed by heating gently.
b. The tight lid of a steel tiffin box is opened by gently heating.
Answer:
a. When you gently heat a tight pen cap, it expands due to thermal expansion of solids because the particles move faster and spread apart. This makes the cap loosen and easier to remove from the pen.
b. When you gently heat the tight lid of a steel tiffin box, the lid expands more than the box itself. This is due to thermal expansion, where the particles in the metal move faster and spread apart when heated. As a result, the lid loosens and becomes easier to open.

Question 26.
What happens to the water level in the refill?
Answer:
The water inside the bottle will expand as it heats up. This causes the water level in the refill tube to rise.

Question 27.
If the water in the injection bottle cools down, will the water level return to its initial position?
Answer:
Yes, if the water in the injection bottle cools down, the water level in the refill tube will go back to its original position. As the water cools, it contracts and takes up less space, causing the level to drop.
Inference

• On heating, the water inside the bottle will expand and cause the water level in the refill tube to rise.
• On cooling, water contracts and the water level is restored.

Question 28.
Place the Aluminium lamp in hot water. What happens? Why?
Answer:
When the Aluminium lamp becomes hot, the air inside it also become hot. As this hot air expands, the coloured water in the tube moves upwards.

Question 29.
Now place the Aluminium lamp in cold water. What do you observe? Why?
Answer:
As the Aluminium lamp cools down, the air contracts, causing the coloured water to move back into the tube and reach its initial position.

Question 28.
Place the Aluminium lamp in hot water. What happens? Why?
Answer:
When the Aluminium lamp becomes hot, the air inside it also become hot. As this hot air expands, the coloured water in the tube moves upwards.

Question 29.
Now place the Aluminium lamp in cold water. What do you observe? Why?
Answer:
As the Aluminium lamp cools down, the air contracts, causing the coloured water to move back into the tube and reach its initial position.

Question 30.
When does the temperature of the atmosphere rise? During the day or at night? Why?
Answer:
The temperature of the atmosphere rises during the day. This happens because the sun heats the Earth’s surface, which then warms the air. As the sun shines, temperatures increase until they usually peak around noon.

Question 31.
Do we experience the same temperature in the morning and at noon? What about the evening?
Answer:
The temperature of the atmosphere rises during the day, peaking around noon when the sun is highest. In the morning, it’s usually cooler because the sun has just risen. By noon, it’s warmer, and in the evening, temperatures start to drop as the sun sets. So, temperatures vary throughout the day.

Question 32.
Can changes in atmospheric temperature cause natural phenomena?
Answer:
Storms, Droughts, Floods, Weather changes etc. The sand and the water on the Earth get heated due to the heat from the Sun.
Soil will heat up faster than water when both are placed in sunlight. This is because soil needs less energy to increase its temperature compared to water.

Let’s do an experiment on a sunny day.

Materials Required: Two glass tumblers, two laboratory thermometers, water, sand.
Take sand in one glass tumbler and water in another as shown in the figure and check the temperature with a laboratory thermometer. Place both the glasses in the sun. Then measure the temperature of sand and water with a thermometer at an interval of 20 minutes and record it in the table.

Time (minutes)	Temperature(0C)
	Sand	Water
20	40	27
40	50	29
60	60	31

Observation
Sand gets heated faster than water.
Now, move both the glasses from the sun to a shade. Measure and record the temperature at an interval of 20 minutes.

Time (minutes)	Temperature(0C)
	Sand	Water
20	60	31
40	55	29
60	50	27

Observation
The sand will cool down faster than water. This is because sand loses heat more quickly than water does when both are moved to a shaded area.

Heat in Everyday Life Class 7 Notes Extra Questions and Answers

Question 1.
Roy and his mother are making tea. He observes and lists down some of the things that happen when tea is made. Those are given in the table below.
A) Complete the table.

B) Observe the picture of the thermoflask.
Write down how each of the parts marked in the picture help to prevent heat loss.

C) Apart from the parts marked in the figure, what are the other arrangements in the thermoflask to prevent heat loss? Write any one.
Answer:
A) i) Conduction
ii) Convection
iii) The heated air
B)
i) The vacuum between double walls – As there is no air, heat loss by conduction is controlled.
ii) Inner surface coated with silver salts – Heat loss by radiation is controlled.

C) Glass vessel and lid – Heat transmission through conduction will be very less.

Question 2.
Observe the picture of the lantern used in the ancient days.

a. When we hold our hand on the top of a burning lamp, we feel hotter. Why?
b. What happens when we close the holes on the lower part of the glass? Write your conclusion.
c. Name the heat transmission method indicated above.
Answer:
a. The air inside the glass gets hot and rises up. So the hand above the flame gets more heat due to convection.
b. It prevents fresh air from being supplied to the lamp, which will cause the flame to go off.
c. Convection

Question 3.
Why are the smoke pipes of factories fixed at a height?
Answer:
This helps to reach the smoke very high and make the burning strong by making a powerful convection flow.

Question 4.
A steel glass containing hot tea is kept on a table. Will the tea become cold after some time, or what are the ways in which the tea loses heat?
Answer:
The tea loses heat by conduction, convection and radiation.

Question 5.
Discuss how the thermal expansion of objects in the following situation is useful.
a) The method of fixing the metal frame to the wheel of the bullock cart.
b) To loosen the cap of a fountain pen that is tightened if it is heated.
c) To take out a glass tumbler that got jammed into another, it is dipped in hot water.
Answer:
a) The metal frame expands while heating. So it slips easily onto the wheel. As the frame cools, it contracts to the original size and fits tightly on the wheel.
b) As the top of the pen is metal it expands more on heating. So we can loosen it easily.
c) When immersed in hot water glass expands. Because of this it is easy to take out a glass tumbler that got jammed into another.

Question 6.
Observe the picture given below.
What are the ways in which heat is transferred in the numbered positions?

Answer:
1 – Convection
2 – Conduction
3 – Radiation

Question 7.
A bottle completely filled with water and tightly closed breaks when it is kept in the freezer of a refrigerator. Why?
Answer:
The water on getting cold becomes ice and expands. So, the bottle completely filled with water and tightly closed breaks when it is kept in the freezer of a refrigerator.

Question 8.
Fill in the blanks suitably
a. It is mainly by ……….. the heat transfer takes place in liquids and gases.
b. A ………is required for heat transfer by conduction and convection.
c. ……….. is the method by which heat is transmitted without the help of the medium.
d. Solids ………. on heating.
e. ……….. works on the basis of the ability of liquids to expand and contract.
Answer:
a. Convection
b. Medium
c. Radiation
d. Expands
e. Thermometer

Question 9.
At which place is a land breeze and sea breeze felt strongly?
A. High Land
B. Mid Land
C. Coastal areas
D. Coastal areas and highland
Answer:
C. Coastal areas

Question 10.
Wind blows from sea to land during the day. What is the reason for this?
Answer:
During day time, the land gets heated up more quickly than the sea. The air above the land gets heated and expands. The air with lower density rises up. The comparatively cooler air above thq sea blows towards the land. This is called sea breeze.

Question 11.
Statements regarding sea breeze and land breeze are given below. Among them select the right ones and classify them.
At night breeze blow from sea to land.
At daytime breeze flow from land to sea.
At night sea gets cooled fast.
At night breeze blow from land to sea.
At night land gets cooled fast.
At daytime the air above the land rises upwards.
At daytime the air above the sea rises upwards.
Answer:

Question 12.
Choose the correct statement from those given below, in relation to the activity you have done.
> Land gets heated sooner during daytime.
> Sea gets heated sooner during daytime.
> During daytime the air above the land gets heated and rises up.
> During night land cools down sooner.
> During night the air above land cools down quickly.
> During night the air above the sea cools down only slowly.
> During night the hot air above the sea rises up.
Answer:
Correct statements are given below:
> Land gets heated sooner during daytime.
> During daytime the air above the land gets heated and rises up.
> During night land cools down sooner.
> During night the air above land cools down quickly.
> During night the air above the sea cools down only slowly.
> During night the hot air above the sea rises up.

Question 13.
The heat from the Sun reaches the Earth by a process called
Answer:
Radiation.

Question 14.
List the given below as good conductors and poor conductors.
Answer:
Good conductors: Copper, Aluminium, Tin, Zinc.
Poor conductors: Wood, Cloth, Plastic, Charcoal, Rubber, Glass.

Question 15.
Gaps are left between sections of rail tracks. Why?
Answer:
Gaps are left between sections of rail tracks to allow for thermal expansion. When the temperature rises, the metal rails expand, and the gaps prevent the tracks from bending. This helps maintain safety and ensures the smooth operation of trains in various weather conditions.

Question 16.
Hot air balloons always rise up. Why?
Answer:
Hot air balloons rise because the warm air inside expands and becomes less dense than the cooler air outside.

Question 17.
A reliable measure of the hotness of an object is its ……….
Answer:
Temperature.

Question 18.
“Temperatures vary throughout the day”. Comment on the statement.
Answer:
The temperature of the atmosphere changes throughout the day. It is usually cooler in the morning when the sun has just risen. By noon, temperatures peak as the Sun is at its highest. In the evening, temperatures begin to drop as the sun sets. Overall, temperatures fluctuate from morning to night.

Question 19.
What is the normal temperature of the human body? How is it measured?
Answer:
The normal temperature of the human body is 37°C (98.6°F). A clinical thermometer is used to measure our body temperature.

Heat in Everyday Life Class 7 Notes

• Heat is a form of energy that can change the state of matter.
• Transmission of heat refers to the flow of heat from one place to another.
• Transference of heat energy from one part to a different part of a body or from one body to another in contact with it, without the actual movement of the molecules, is called conduction.
• Substances that allow heat to pass through them well by conduction are called good conductors and those substances that do not allow heat to pass through them well are called poor conductors.
• Convection is the process of heat transfer in fluids (liquids and gases) through the movement of molecules.
• Radiation is the transfer of heat without needing a medium. Heat moves in all directions through radiation.
• If we are able to prevent the transfer of heat by conduction, convection and radiation, we can keep hot objects hot and cold objects cold for a long time.
• Solids, Liquids, and Gases expand on heating and contract on cooling.
• Temperature is a measure of the hotness or coldness of an object.
• A clinical thermometer is used to measure body temperature.
• A laboratory thermometer is an instrument used in a laboratory to measure temperature.
• Atmospheric temperature refers to the temperature of the air in the Earth’s atmosphere.
• A sea breeze occurs because land heats up and cools down faster than water. During the day, the land becomes warmer than the sea, causing the air above the land to heat up, expand, and rise.