Thermal Radiation

DONE BY:NUJOOD AL-HASHARABRAR AL-HADDABI

KAWTHAR AL-LAWATIMARIA AL-WAHAIBI

The sun’s energy travels to us in a vacuum. they can travel through a vacuum (empty space). They heat up things that absorb them, so are often called thermal radiation.

Thermal Radiation

All objects give out some

thermal radiation. The higher their surface

temperature and the greater their surface area, the more energy they radiate per second.

Warm objects radiate infrared.

Thermal Radiation

Thermal

radiation is

mainly infra

red

waves, but

very hot

objects also

give out light

waves.

Some surfaces are better

at emitting (sending out) thermal radiation than others. For example a black saucepan cools down more quickly than a similar white one because it emits energy at a faster rate.

Emitters and absorbers

Dull, black

surfaces are

better

absorbers

than

shiny/white

surfaces.

Emitters and absorbers

Shiny/white

surfaces are

better

reflectors

than dull

black

surfaces.

Emitters and absorbers

This chart

shows how

some surfa

ces

compare as

emitters,

reflectors,

and

absorbers of

thermal

radiation.

Comparing emitters

The metal cube is filled with boiling water which heats the surfaces to the same temperature.

The thermal radiation detector is placed in turn at the same distance from each surface and the meter readings are compared.

Comparing absorbers

The metal plates are placed at the same distance from a radiant heater.

To find out which surface absorbs thermal radiation most rapidly, the rises in temperature are compared.

Emitters and absorbers

Comparing emitters

Comparing absorbers

Emitters and absorbers

A solar panel uses the sun’s

thermal energy to worm up water for houses.

The blackened layer absorbs the radiant energy and warms up water flowing through the pipes.

Solar panel

A vacuum flask can keep drinks hot or

cold. It has these features for reducing the rate

at which thermal energy flows out or in:1. An insulated stopper to reduce

conduction and convection.2. A double-walled container with a gap

between the walls. Air has been removed from the gap to reduce conduction and convection.

3. Walls with silvery surfaces to reduce thermal radiation.

Vacuum flask

Refrences

BookComplete Physics for IGCSE

By Stephen Pople