A Crookes Tube. Credit: Wikipedia |
His work on electricity in high vacuum, leads us to cathode rays tubes (the technology behind the creation of television).The Crookes tube is an early experimental electrical discharge tube, with partial vacuum, in which cathode rays, streams of electrons, were discovered. The Crookes tube consists of a partially evacuated glass container of various shapes, with two metal electrodes, the cathode and the anode, one at either end. When a high voltage is applied between the electrodes, cathode rays (electrons) are projected in straight lines from the cathode. It was used by Crookes, Johann Hittorf, Julius Plücker, Eugen Goldstein, Heinrich Hertz, Philipp Lenard and others to discover the properties of cathode rays, culminating in J.J. Thomson's 1897 identification of cathode rays as negatively charged particles, which were later named electrons.
Crookes tubes are now used only for demonstrating cathode rays.
Crookes radiometer in action. Credit: wikipedia |
It is still manufactured and sold as an educational aid or curiosity.
The radiometer is made from a glass bulb from which much of the air has been removed to form a partial vacuum. Inside the bulb, on a low friction spindle, is a rotor with several (usually four) vertical lightweight metal vanes spaced equally around the axis.
The vanes are:
The vanes are:
- polished or white on one side,
- black on the other.
When exposed to sunlight, artificial light, or infrared radiation (even the heat of a hand nearby can be enough), the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing.
Cooling the radiometer causes rotation in the opposite direction.
Cooling the radiometer causes rotation in the opposite direction.
To know more see radiation pressure.
Fonts:- How does a light-mill work?-Physics FAQ
- The Cathode Ray Tube site
- Bell, Mary; Green, S. E. (1933), "On Radiometer Action and the Pressure of Radiation", Proceedings of the Physical Society 45 (2): 320–357,Bibcode:1933PPS....45..320B, doi:10.1088/0959-5309/45/2/315. 1933 Bell and Green experiment describing the effect of different gas pressures on the vanes.
- The Properties of the Force Exerted in a Radiometer
- Crookes' Radiometer, Wikipedia, April, 04, 2014
Videos about radiation pressure:
No comments:
Post a Comment