NCERT Class 7th Science Chapter 4 Heat, NCERT Science Solutions,NCERT Solutions,NCERT Solutions Class 7, www.educationphile.com, Heat, Conduction, convection, radiant heat, sea breeze, land breeze

Chapter 4
Heat


In winters we wear woollen clothes and in summer we wear cotton clothes we wear clothes according to the season. When we are outside we feel hot in summer, so how we find something is hot or cold.



Examples of Hot and Cold
Examples of Hot and Cold


Hot and Cold
We can feel hot or cold by our sense of "touch". It is not reliable all the time so we use some device to measure the exact temperature and that is called as thermometers.

Measuring Temperature
We know that when someone is ill, doctor use thermometer to measure the temperature of the body and this thermometer is called Clinical ThermometerThe clinical thermometer has a temp. range from 35°C to 42°C and Fahrenheit is 94 to 108.   

Clinical Thermometer, Class 4 heat, ncert class 7 chapter 4
Clinical Thermometer

Laboratory Thermometer

For other objects, we use laboratory thermometer is used.
Different types of thermometers are used for different purposes. The maximum and minimum temperatures of the day, shown in weather reports, are measured by a thermometer known as a maximum-minimum thermometerLaboratory thermometer can measure temperature from -10 °C to 110 °C.

Clinical Thermometer
Laboratory Thermometer


Mercury is very toxic for health that’s why nowadays digital thermometer is being used. 

Digital Thermometer
Digital Thermometer

TRANSFER OF HEAT

We have seen when we heat a frying pan or any utensils we can feel the heat in the handle, why? Because of the transfer of heat.


Types of Heat Transfer, NCERT Class 7th Science Chapter 4 Heat
Modes of Heat Transfer

Conduction (प्रवाहकत्त्व)

The Process by which heat is transferred from the hotter end to the colder end of an object is known as conduction. In solids, heat is mostly transferred by conduction.


Conduction, NCERT Class 7th Science Chapter 4 Heat
Conduction
Conductors à the materials which allow heat to pass through them called as Conductors, for example:- iron, copper, aluminium, etc.

Insulators à The material which does not allow heat to pass through them as called as Insulators, for example:- wood, plastic, ceramic, etc. water and air are poor conductors of heat.

Convection (संवहन)

When the water is heated, the water near the flame gets hot. Hot water rises up. The cold water from the sides moves down towards the source of heat. This process repeats and whole water gets heated; this process of heat transfer is known as convection.

Convection, NCERT Class 7th science, Chapter 4: Heat
Convection

People of coastal area experience a phenomenon.

Sea Breeze
The air from the sea flows and replaces the hot air of land and this cycle continues in the day time, this happens when land gets hotter faster than the water in the day time.

Sea Breeze, Convection of air, NCERT Class 7 science, chapter 4: Heat
Sea Breeze

Land Breeze
In the night time reverse is happens water get cooler more slowly than the land and cool air flows from land to water this phenomenon is called as Land Breeze.

Land breeze, NCERT Class 7 science, Chapter 4: Heat
Land breeze

Radiation (विकिरण)

Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object.


Radiation (examples of Radiant Heat), NCERT Class 7th Science Chapter 4 Heat
Radiation
Kinds of Clothes We Wear in summer and winter
We prefer light-coloured clothes in summer and in winter we usually wear dark-coloured clothes because the dark colour absorbs more heat.

In winter we wear woollen clothes because wool is a poor conductor of heat and air traps in woollen fibres. This air prevents the loss of heat from our body to the cold surroundings. That’s why we feel warm.

Effect of the colour and Woollen clothing, NCERT Class 7th Science Chapter 4 Heat
Effect of the colour and Woollen clothing

Exercise:
1. State similarities and differences between the laboratory thermometer and the clinical thermometer.
Answer:
Similarities: Both are used to measure temperature.
Both have mercury in it.

Differences: 
Clinical Thermometer
1. The temperature range in the thermometer is 35°C to 42°C.
2. It is used for clinical purposes only.
3. They have the kink to prevent the flow of mercury by its own.

laboratory thermometer
1. In laboratory thermometer, the temperature range is –10 °C to 110 °C.
2. It is used in labs where temperature range is large.
3. They do not have kink. 

2. Give two examples each of conductors and insulators of heat.
Answer: 
Conductor: Iron and Copper
Insulator: Wood and Plastic

3. Fill in the blanks:
(a) The hotness of an object is determined by its Temperature.
(b) The temperature of boiling water cannot be measured by a Clinical thermometer.
(c) Temperature is measured in degree Celsius.
(d) No medium is required for transfer of heat by the process of radiation.
(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of Conduction.
(f) Clothes of dark colours absorb heat better than clothes of light colours.
4. Match the following:

(i) The land breeze blows during
 (d) Night
(ii) The sea breeze blows during
(c) day
(iii) Dark coloured clothes are preferred during
(b) winter
(iv) Light coloured clothes are preferred during
(a) summer

 5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Answer: More layers of clothes help to retain the heat and we feel warmer instead of one thick clothing.

6. Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.


7. In places of the hot climate, it is advised that the outer walls of houses be painted white. Explain.
Answer: White colour does not absorb heat and helps to reflect the light that’s why it is advised to paint the buildings in white colour

8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be
(a) 80°C (b) more than 50°C but less than 80°C
(c) 20°C (d) between 30°C and 50°C
Answer: (d) between 30°C and 50°C

9. An iron ball at 40°C is dropped in a mug containing water at 40°C.
The heat will
(a) Flow from iron ball to water.
(b) Not flow from iron ball to water or from water to iron ball.
(c) Flow from water to iron ball.
(d) Increase the temperature of both.
Answer: (b) Not flow from iron ball to water or from water to iron ball. Because both have the same temperature.

10. A wooden spoon is dipped in a cup of ice cream. Its other end
(a) becomes cold by the process of conduction.
(b) becomes cold by the process of convection.
(c) becomes cold by the process of radiation.
(d) does not become cold.
Answer: (d) does not become cold.


11. Stainless steel pans are usually provided with copper bottoms. The reason for this could be that
(a) Copper bottom makes the pan more durable.
(b) Such pans appear colourful.
(c) Copper is a better conductor of heat than the stainless steel.
(d) copper is easier to clean than stainless steel.
Answer: (c) Copper is a better conductor of heat than the stainless steel.

Keywords: Celsius scale, Conduction, Conductor, Convection, Insulator, Land breeze, Radiation, Sea breeze, Temperature, Thermometer, NCERT Free Solutions, CTET Paper-II, CTET TGT, KVS, UPSC.
All Rights Reserved to educationphile.com

Post a Comment

Thank you for visiting

Previous Post Next Post