CBSE Class 7 Science Chapter 4 Notes Heat
Heat Class 7 Notes Understanding the Lesson
1. Heat is a form of energy.
2. The hotness and coldness of a body is relative.
3. Our sense of touch is not always a reliable guide to the degree of hotness of an object.
4. The measure of degree of hotness of an object is called temperature.
5. Thermometer is a device which is used to measure temperature.
6. The thermometer that measures our body temperature is called a clinical thermometer.
7. Clinical thermometer consists of a long, narrow, uniform glass tube and a bulb at one end. It has a kink which prevents mercury level from falling on its own. The range of this thermometer is from 35°C to 42°C (Fig. 4.1).
8. The normal temperature of human body is 37°C.
9. To measure the temperature of non-living objects, a laboratory thermometer is used. The range of laboratory thermometer is from -10°C to 110°C. (Fig. 4.2).
10. Nowadays, a digital thermometer is used instead of a clinical thermometer. It has no mercury in it.
11. Heat always flows from higher temperature to lower temperature. The three ways in which heat can flow from one object to another are conduction, convection and radiation.
12. The process by which heat is transferred from the hotter end to the colder end of an solid object is known as conduction.
13. The materials which allow heat to pass through them easily are called conductors. For example, iron, copper, zinc, etc.
14. The material which do not allow heat to pass through them easily are called poor conductors or insulators. For example, plastic, rubber, wood, etc.
15. Convection is the process of transferring heat from a hotter region to cooler region by the actual movement of particles. It generally occurs in liquid and gaseous medium.
16. Convection takes place when the air near the heat source gets hot and rises. The air from sides comes in to take its place.
17. The flow of cool air from the sea towards the land to replace the hot air on land, is called sea breeze [Fig. 4.3(a)]. This phenomenon takes place during the day.
18. During the night, the currents of air flow from the cooler land towards the warmer sea. This is called land breeze. [Fig. 4.3(b)],
19. The process of transmission of heat without any contact between the source and the object is called radiation.
20. All hot bodies radiate heat.
21. Dark-coloured objects absorb radiation better than the light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.
22. Woollen clothes keep us warm during winter. This is because wool is a poor conductor of heat and it has air trapped in between the fibres.
Class 7 Science Chapter 4 Notes Important Terms
Celsius scale: Celsius scale or centigrade scale is the unit used for measurement of temperature. It is a metre scale of temperature.
Conduction: The process by which heat is transferred from the hotter end to the colder end of an object is known as conduction.
Conductor: The material which allow heat to pass through them easily is called conductor.
Convection: The process of transferring heat from a hotter region to cooler region by the actual movement of particles is called convection.
Insulator: The material which do not allow heat to pass through them easily is called insulator.
Land breeze: The process of flowing of air currents from the cooler land towards the warmer sea is called land breeze.
Radiation: The process of transfer of heat in which no medium is required is called radiation.
Sea breeze: The flow of cool air from the sea towards the land to replace the hot air on land is called sea breeze.
Temperature: The reliable measure of the hotness of an object is called temperature.
Thermometer: A device used to measure the temperature is called thermometer.