Quick Answer: Crookes Radiometer is a partially evacuated glass bulb containing lightweight vanes on a spindle; in sunlight or bright light the vanes rotate, demonstrating the effect of radiant energy.
Last updated: October 2026
Key Features
Low-pressure glass bulb with a rotating vane assembly on a spindle support
Vanes have black and light reflective surfaces
Works in sunlight or under a bright light source; no electricity needed
Different light intensities can be used to compare the speed of vane rotation
Delicate glass bulb: handle with care
Technical Specifications
Specification
Value
Product type
Physics radiation demonstration instrument
Material
Glass bulb, lightweight vane assembly, spindle support
Components
Transparent bulb, rotating vanes, black and light reflective surfaces
Operation
Observation under sunlight or bright light source
Usage level
Secondary to undergraduate physics
About This Product
Placed on a stable surface and exposed to sunlight or a bright light, the radiometer gives a class a direct view of light-induced motion, which teachers use to discuss radiant energy, heat absorption and low-pressure gas behaviour. Comparing vane speed under different light intensities turns this Physics Miscellaneous Products demonstration into a simple investigation.
Frequently Asked Questions
Q1. Does the Crookes Radiometer need electricity? No. It works through exposure to sunlight or another bright light source.
Q2. What happens when the radiometer is placed in light? The vane assembly inside the low-pressure bulb begins to rotate, and the rotation speed changes with light intensity.
