Radiation

1. Radiation

2. Heat from the Sun reaches the Earth by radiation What is Radiation? Radiation is the third process of heat transfer ( the other two types are conduction and convection).Radiation is a type of electromagnetic waves of different frequencies and wavelengths but with the same speed in vacuum. It is the continual emission of infra-red waves from the surface of the bodies, transmitting through space, without the aid of a material medium. It can take place in a vacuum. For example, heat from the Sun reaches the Earth by the process of radiation.

3. Infra-red Radiation • Absorption of infra-red radiation Infra-red radiation is absorbed by all objects and surfaces. The absorption causes a temperature rise. Heat due to infra-red waves are called radiant heat. The hotter the object, the greater is the amount of radiant heat emitted. • Emission of infra-red radiation Infra-red radiation is emitted by all objects and surfaces. This emission causes the temperature to fall.

4. Factors affecting the rate of transfer of energy by radiation • Colour and texture of the surface Dull, black surfaces are better emitters of infra-red radiation than shiny, white surfaces. The rate at which infra-red radiation is emitted is higher if the surface is dull and black. • Surface Temperature The rate of transfer of energy by radiation also depends on the surface temperature. The higher the temperature of the surface of the object is relative to room temperature, the higher the rate of energy transfer. • Surface Area The third factor which affects the rate of transfer of energy by radiation is the surface area of the object. If we compare two objects of the same mass and made of the same material, but having different surface areas, the object with the larger surface area will emit infra-red radiation at a higher rate.

5. Consequences of Radiation • Colour and texture of clothing On sunny days, wearing dull, black clothes will be much more uncomfortable than wearing shiny, white clothes due to the large amount of radiant heat absorbed. • Skin cancer With the damage done to the ozone layer in the atmosphere, human beings are increasingly exposed to harmful radiation from the Sun. The ultraviolet radiation from the Sun is one of the causes of skin cancer.

6. Since shiny surfaces are bad emitters of radiation, shiny teapots can keep tea warmer than a black teapot for a longer time. In addition, since shiny surfaces are bad absorbers of radiation, shiny containers can keep a cold liquid cooler for a longer time than black containers. Shiny teapot Everyday applications of radiation • Vacuum flasks The vacuum flask is designed to keep liquids hot by minimising heat losses. Heat loss by radiation is harder to stop as radiant heat can pass through a vacuum. To minimise heat loss through radiation, the walls of the glass are silvered so as to reflect the radiant heat back into the hot liquid. • Teapots

7. Glass Roof Infra-red radiation from the sun Glass sides Plants and soil absorb radiation and emit radiation with longer wavelengths which are trapped inside the greenhouse • The greenhouse On a warm day, infra-red radiation from the Sun passes through the glass of the greenhouse and is absorbed by the soil and plants inside. The soil and the plants therefore become warmer and they emit infra-red radiation of longer wavelengths as they are a lower temperature source compared to the Sun. These longer wavelengths of radiation are unable to pass through the glass( the glass lets in the short wavelength radiation from the Sun, but acts as a shield to outgoing long wavelength radiation) and so heat is trapped inside the greenhouse. This causes the temperature inside the greenhouse to rise and this is good for plant growth.

8. Questions

9. Q1. What is radiation? Answer: Radiation is a type of electromagnetic waves of different frequencies and wavelengths but with the same speed in vacuum. It is the continual emission of infra-red waves from the surface of the bodies, transmitting through space, without the aid of a material medium. Q2. When Infra-red radiation is absorbed, what happens to the temperature? Answer: The temperature will rise. Q3. What are the factors that affect the rate of transfer of energy by radiation? Answer: Colour and texture of the surface Surface temperature Surface area

10. Q4. What are the consequences of radiation? Answer: On sunny days, wearing dull, black clothes will be much more uncomfortable than wearing shiny, white clothes due to the large amount of radiant heat absorbed. With the damage done to the ozone layer in the atmosphere, human beings are increasingly exposed to harmful radiation from the Sun. The ultraviolet radiation from the Sun is one of the causes of skin cancer. Q5. What are the everyday applications of radiation? Answer: The vacuum flask is designed to keep liquids hot by minimising heat losses. Heat loss by radiation is harder to stop as radiant heat can pass through a vacuum. To minimise heat loss through radiation, the walls of the glass are silvered so as to reflect the radiant heat back into the hot liquid.

11. Since shiny surfaces are bad emitters of radiation, shiny teapots can keep tea warmer than a black teapot for a longer time. In addition, since shiny surfaces are bad absorbers of radiation, shiny containers can keep a cold liquid cooler for a longer time than black containers. On a warm day, infra-red radiation from the Sun passes through the glass of the greenhouse and is absorbed by the soil and plants inside. The soil and the plants therefore become warmer and they emit infra-red radiation of longer wavelengths as they are a lower temperature source compared to the Sun. These longer wavelengths of radiation are unable to pass through the glass( the glass lets in the short wavelength radiation from the Sun, but acts as a shield to outgoing long wavelength radiation) and so heat is trapped inside the greenhouse. This causes the temperature inside the greenhouse to rise and this is good for plant growth.

12. Thank You For your attention Done By: Joash Kai Siang Jason Daniel