Heat - Revision Notes

 CBSE Class 7 Science

Revision Notes 
Chapter – 4
Heat

  • Heat: It is a form  of energy, which makes any object hot or cold.
  • Temperature:  The degree of hotness  of an object is called temperature.
  • Our sense of touch is not reliable to measure the temperature.
  • Thermometer is a device used for measuring temperatures.
  • Heat is the cause of temperature.
  • Clinical thermometer is used to measure our body temperature. The range of this thermometer is from 35°C to 42°C.  For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from –10°C to 110°C.
  • The normal temperature of the human body is 37°C.
  • The materials which allow heat to pass through them easily are conductors of heat.
  • The materials which do not allow heat to pass through them easily are called insulators.
  • Clinical Thermometer: It is a thermometer used to measure the temperature of our body. It consists of a long, narrow, uniform glass tube with a bulb containing mercury at one end. There is a kink near the bulb. It reads a range of temperatures from  94°F to 108°F(35°C and 42°C).
  • Laboratory Thermometer: It is a thermometer used to measure the temperature of objects other than our body. It consists of a column of mercury enclosed in a glass casing. The column is continuous without any kink. It measures a range of temperature from -10˚C to 110˚C
  • Sea Breeze: Durign the day, the land heats up faster than the sea.
  • Warm air above the land rises and cold air from sea takes its place.
  • Warm air from the land moves towards the sea to compele the cycle.
  • This produces a sea breeze from the sea to the land.
  • Land Breeze: At night the land cools faster than sea.
  • The warm air above the sea rises.
  • This warm air is replaced by colder air from the land producing a land breeze
  • Transfer of Heat: Heat flows from a hotter object to a colder object until both objects reach the same temperature.
  • The heat flows from a body at a higher temperature to a body at a lower temperature. There are three ways in which heat can flow from one object to another. These are conduction, convection and radiation.
  • Conduction: It is the process by which heat is transferred from the hotter end to the colder and end of an object.
  • Convection: It is the flow of heat through a fluid from places of higher temperature to places of lower temperature by movement of the fluid itself.
  • Radiation: It is the mode of transfer of heat in which energy is directly transferred from one place to another. It does not need any material medium.
  • 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.
  • Woollen clothes keep us warm during winter. It is so because wool is a poor conductor of heat and it has air trapped in between the fibres.