7th Class Science Heat Radiation of Heat

       Radiation of Heat

Heat from the Sun comes down on the surface of the Earth through atmosphere. A major part of solar radiation is reflected into space by atmosphere. Only some part of radiation comes on the surface of the earth. In the figure below, 25% of solar radiation is reflected by wind and 3% of solar radiation is reflected by the earth surface.

Look at the following picture of solar radiation

                                       Solar Radiation

In the figure below, a bundle of wood stick burns and radiates heat energy.                

              Radiation  

Air around the fire gets heated first and moves upward. To fill the air gap, cold air comes around the fire and gets heated too. Our hands near the fire feel heat due to the radiation of heat.                                      

Radiation of heat energy is useful for the human being. The temperature of the human body is 98.4°F and should be constant. Air, around the fire, is heated due to convection of heat. Other end of the iron rod, which is away from fire, is heated by the conduction of heat. In the following figure, a solar plate converts solar radiation into electrical energy.

Look at the following picture of radiation of heat

      Which one of the following reflects more heat energy, coming from Sun, into space?

(a) Surface of the earth

(b) Atmosphere of the earth

(c) Core of the earth

(d) All of these

(e) None of these

Answer: (b)

      Whole part of the iron rod is heated by heating just its one end. Which one of the following features of iron is responsible for the same?

(a) Iron is the poor conductor of heat

(b) Iron is the good conductor of heat

(c) Iron is the insulator of heat

(d) All of these

(e) None of these

Answer: (b)