This demonstration shows how light energy can be transformed into both thermal and mechanical energy using a radiometer. The black sides of the vanes absorb more light and heat up more than the white sides. Air molecules striking the heated black surfaces gain more energy and rebound with greater force than those striking the white sides, causing the vanes to spin. A partial vacuum inside the bulb reduces resistance, making the effect easier to see.

1. Place a radiometer under a bright lamp or in direct sunlight.
2. Observe the vanes spinning inside the glass bulb.
3. Adjust the distance of the light source to see how brightness affects the speed.

The Radiometer - See the Energy of Light! - Arbor Scientific:

How a Crookes radiometer works - Applied Science :

📄 Radiometer - Science World: https://www.scienceworld.ca/resource/radiometer/

• Compare sunlight vs. artificial light.
• Test different lamp intensities or LED vs. incandescent bulbs.
• Record spin rates at different distances from the lamp.
• Use colored filters to see how wavelength affects energy absorption.

• Handle radiometer carefully – the glass bulb is fragile.
• Avoid using excessively hot lamps too close to the bulb to prevent overheating.
• Supervise students when using electrical lamps.

• What role does the partial vacuum play in the radiometer?
• Why do the black sides heat up more than the white sides?
• What would happen if both sides of the vanes were the same color?
• How does this demonstration connect to everyday experiences, like wearing dark vs. light clothing in the sun?