Fred wrote: > Astute calculations show that dissociation > of an Iodine molecule at the filament, with > uptake and subsequent discharge of an > electron attached to an Iodine atom > at the bulb (internal) reflector coating could > yield up to 20 amperes at ~ 0.5 volts from > the 12 watts of solar energy focused on > filament of 1 square cm area.
But here's the problem. The quartz halogen bulbs are usually small quartz tubes isolated from the reflectors, as opposed to something like the heat lamp you tried where there is a partial vacuum within the entire bulb including the outer envelope and the reflector. Usually, such bulbs have no halogens, but are simply argon filled at low pressure. You wouldn't want to use a floodlamp anyway, because by definition, their reflectors are not parabolic, but elliptical, and usually include some diffusion besides. Not a particularly good candidate for solar concentration. Please pardon me for being excessively punctilious about this, but I've actually played around with this basic idea for years. However, I never thought of a Langmuir type dissociation, but was merely entranced with the idea of solar driven vacuum tube thermo- electricity. I have in fact used old radio amplifier vacuum tubes, externally heating the filaments with focused sunlight. This produced encouraging but not useful results. The filaments are never really the right shape to get the desired concentration. Ditto lightbulbs. You would probably need a custom built tube to take advantage of the effect you would like to demonstrate. It wouldn't be a bad idea to resurrect Philo Farnsworth and ask him how to do it. The guy probably knew more about the practical aspects of vacuum tube thermo- electrics than anyone before or since. Anyone out there channeling Philo? ;-) Here's an odd possiblity, though. If you want to try to extract a charge from the internal reflector, you could try attaching aluminum foil to the outside of the bulb and then vary the exposure to sunlight. This would give a time varying charge to the reflector and then the capacitive coupling the the external foil might result in an accessible AC current. Just a thought. M. _______________________________________________ Join Excite! - http://www.excite.com The most personalized portal on the Web!
