Crookes Radiometer

The Crookes Radiometer is a light-responsive physics apparatus used to demonstrate thermal transpiration and molecular effects in a rarefied gas. Intended for supervised school, college and STEM laboratories, it helps learners connect light absorption, differential heating, gas behaviour and mechanical rotation without electrical power for the radiometer itself.

Product Description

The STEMAids Crookes Radiometer is based on a sealed, partially evacuated transparent bulb containing a low-friction rotor. In the standard design, each vane has a dark, light-absorbing face and a reflective face. Illumination heats the dark faces more strongly, creating temperature-dependent forces in the low-pressure gas around the vane edges.

The resulting rotation demonstrates rarefied-gas thermodynamics, not a direct measurement of photon pressure. Its visible response supports classroom investigation and discussion of historical explanations. Browse related physics laboratory products and educational science models.

Key Features

• Visible energy conversion: Converts differential heating into observable rotor motion.
• Rarefied-gas demonstration: Introduces thermal transpiration, thermal creep and mean-free-path concepts.
• Contrasting vane surfaces: Uses dark and reflective faces to produce unequal heating.
• No internal electrical supply: Responds to a suitable external light or heat-radiation source.
• Compact classroom model: Supports demonstrations, laboratory observation and science exhibitions.
• Low-friction rotation: Makes small thermally generated forces visible.
• Honest measurement scope: Intended for qualitative demonstration unless supplied with calibration.

Technical Specifications

What’s Included in the Kit

• Sealed Crookes Radiometer bulb assembly
• Internal vane rotor and low-friction support
• Base or stand
• Instruction sheet
• External light source

Applications / Uses

• Demonstrating unequal radiant-energy absorption.
• Introducing thermal transpiration and reduced-pressure gas behaviour.
• Comparing dark and reflective surface heating.
• Discussing conversion of radiant energy into motion.
• Correcting the misconception that rotation is caused mainly by radiation pressure.
• Supporting thermodynamics lessons and science exhibitions.

How to Use the Crookes Radiometer

1. Inspect the bulb for cracks, chips or a loose base.
2. Place it upright on a stable surface away from the bench edge.
3. Allow the rotor to become stationary.
4. Expose the vanes broadly to sunlight or a suitable lamp from a safe distance.
5. Observe the rotation; the dark faces normally retreat from stronger illumination.
6. Change the source distance gradually and record qualitative differences.
7. Remove the source and allow the apparatus to cool before storage.

Safety and handling: The evacuated bulb is fragile. Do not shake, drop, open or heat it with a flame. Avoid focused beams and keep hot lamps away from the glass. Use under supervision.

Care & Maintenance

• Dust the exterior with a soft, dry cloth.
• Hold the apparatus by its base, not the bulb.
• Store upright in a padded, dry cabinet away from vibration and heat.
• Stop using the unit if the bulb is cracked or loose.

Why Choose STEMAids

STEMAids manufactures educational science models, laboratory products, STEM kits and teaching-learning resources. Its official website states that development is supported by in-house research, educational expertise and quality assurance. The company supports customized and bulk institutional requirements for domestic and international buyers. Explore related microscope and optics equipment or the Helium Neon Laser.

Frequently Asked Questions

What is a Crookes Radiometer used for?

It demonstrates how differential vane heating produces motion through molecular effects in a partially evacuated bulb.

Does a Crookes Radiometer prove radiation pressure?

No. Photon pressure exists, but rarefied-gas thermal effects dominate the familiar rotation.

Why are the vanes black on one side and reflective on the other?

The dark side absorbs more radiant energy and becomes warmer. This temperature difference drives gas-related forces near the vane edges.

Does the radiometer need electricity?

The radiometer needs no electrical connection. It requires suitable external illumination from sunlight or a compatible lamp.

Can it be used in school laboratories?

Yes. It suits supervised physics lessons and exhibitions when the fragile bulb is handled carefully.

Can it measure light intensity accurately?

Use it qualitatively unless STEMAids supplies a calibration. Rotation is also affected by temperature, pressure, friction and source geometry.

Request the confirmed dimensions, vane configuration and packing list from STEMAids, then view the Physics Lab Products category.