Experience this sphere powered by the sun! The vanes in the Radiometer are alternately dark and light in color. When the light strikes these vanes it transfers heat to each one - but not at the same degree. The lighter vane reflects the rays and the darker vane absorbs the rays. The stronger the light, the more energy there is causing the vanes to spin faster.
The radiometer is a light bulb shaped device containing an object that looks like a weather vane (wings arranged in a circle like spokes of a wheel). Developed to measure the intensity of radiant energy, or heat, the radiometer will:
1) Help you understand the principles of energy conversion.
2) Show how heat and mechanical energy are products of energy conversion.
Most of us don’t realize how important energy is in our lives. In actuality, every facet of our life involves energy. One of the reasons we tend to take energy for granted is that it is constantly changing from one form to another. We call this change energy conservation.
During this conversion, energy is changing to and from potential and kinetic forms of energy. Potential energy is the energy stored in matter; kinetic energy is the energy of motion. In all energy conversions, the useful energy output is less than the energy input. This is because some energy is used to do work, and some energy is converted to heat.
The original radiometer was invented by Sir William Crookes in the mid-nineteenth century. The device was developed to measure the intensity of radiant energy, or heat.
What causes the vanes of the radiometer to spin? The atmosphere inside a radiometer is a nearly perfect vacuum. More than 99% of the air has been removed, leaving only thousands of air molecules inside the radiometer compared to the trillions of molecules in the outside atmosphere. The “lighter air” inside the radiometer means that the air molecules are able to move about more freely.
The opposing sides of each vane within the radiometer are alternately dark and light in color. As light (infrared radiation) hits the vanes, the lighter side reflects the light while the dark side absorbs the radiant energy, a difference in temperature develops between the vanes. The freely moving air molecules bounce off the dark side with a great deal of energy. As the air molecules push away from the dark side of the vane, they form convection currents and momentum transfer causing the vanes to spin away from the side from which they pushed (that is away from the dark side of the vane).
Stronger light means that more energy will be absorbed on the dark side, and the air molecules will “kick off” faster and with greater force. Therefore, as the light gets brighter, the vane begins to spin faster and faster.
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