Thermal radiation and surface radiation

Energy and Energy Resources

Starter Activity

Energy is ability to do work.

The unit of energy is Joule(J)

Forms of energy;

Light energy, Heat energy, Electrical energy, Sound energy, Kinetic energy, Potential energy (Gravitational or Elastic) and Chemical energy.

By the end of the lesson pupils should know that;

objects give off thermal radiations depending on the temperature of an object.

surfaces emit and absorb radiations.

Thermal Radiation, Conduction, Convection, Green house effect, Electromagnetic spectrum, Wave length, Gammer rays, infrared, ultraviolet rays, visible light, X-ray, radio wave,

In pairs;Discuss how heat energies is transferred

in A, B and C in the above diagram

In groups of three;Discuss why the body of the above animals are showing different colours .

Every objects gives out (emits) different amounts of thermal radiation depending on their temperature and their surface .

The hotter an object, the more thermal radiation it emits (e.g Sun ).

The red part on the animals indicate that area has more heat ( the region is richly supplied with blood).

The blue parts of the animal indicate that the area is cold (has less heat)

Turn to page 229 and read Energy from the Sun.

Using information from the page above, discuss the following in pairs;

1. How does heat energy from the sun reach us on earth?

2. What happens to most of the radiations in the Earth’s atmosphere?

The sun emits radiation in form electromagnetic waves.

Earth’s atmosphere blocks most of the radiation, such as ultraviolet rays.

But it doesn’t block thermal radiation.

What is green house effect?

The Earth’s atmosphere acts like a greenhouse made of glass.

In a green house , shorter wavelengths radiation from the sun can pass through the glass.

Longer wavelength thermal radiation is trapped inside by the glass, making the greenhouse warm.

1. What are the green house gases ?

2. And how do they cause green house effect?

1. Carbon dioxide

2. Methane

3. Water vapour

These gases absorbs the Earth’s infrared radiation

Look at the pictures below and in pairs;

Discussed why the thermal blanket and fire suit have shiny outer surface and the car radiator is painted black?

Fir

e M

an

Car Radiator

Th

erm

al B

lan

ket

Dull black surface loses energy more quickly; its a good radiator and good absorber. It takes in and give out a lot of radiation. That’s why car radiators and motor bike engine are painted black in colour.

The shiny surfaces reduces radiation (and convection and evaporation). It is a poor radiator and poor absorber. That’s why the thermal blankets and fire suit have shiny outer surfaces.