Heat transfer by radiation
Radiation is the transfer of heat energy from a region of high temperature to a region of low temperature by infrared radiation.
Unlike conduction and convection, radiation takes place without the need of any particles.
Because no particles are involved, radiation can work through the vacuum of space.
This is why we can still feel the heat of the Sun even though it is 150 million km away from the Earth.
Heat radiation investigation
The transfer of infrared radiation from a hot object to cooler surroundings can be investigated using a piece of apparatus called a Leslie cube.
This is a metal cube with four side prepared in different ways: black, white, shiny, or dull.
It can be filled with hot water or heated on an electrical hot plate so that all four sides are at the same temperature.
Method
- Measure the temperature a fixed distance from each side of a Leslie cube using four identical thermometers.
- Heat the Leslie cube by filling it with boiling water.
- Continue to measure and record the temperatures every 30 seconds for five minutes, then plot a graph of temperature on the y-axis, against time on the x-axis, for each side.
- Compare the four graphs obtained.
Control Variables
Distance of each thermometer from the sides of the cube, the type of thermometer used and the time taken for each reading.
Results
The temperature of the thermometer opposite the dull, black side reaches the highest temperature in the same time interval.
From this we can say that dark matt surfaces are better at radiating heat energy than light shiny surfaces.
