Page Text
________________
present around it. One of Thomas Edison's main contributions to the development of such bulbs was learning how to extract all the air from the bulb. But a bulb that contains no gas won't work well because tungsten sublimes at high temperature..... its atoms evaporate directly from solid to gas. If there were no gas in the bulb, every tungsten atom that left the filament would fly unimpeded all the way to the glass wall of the bulb and then stick there forever. While there are some incandescent bulbs that operate with a vacuum inside, most common incandescent lamps contain a small amount of argon and nitrogen gases.
Argon and nitrogen are chemically inert, so that the tungsten filament can't burn in the argon and nitrogen, and each argon atom or nitrogen molecule is massive enough that when a tungsten atom that's trying to leave the filaments hits it, that tungsten atom may rebound back onto the filament. The argon and nitrogen gases thus prolong the life of the filament. Unfortunately, these gases also convey heat away from the filament via convection. You can see evidence of this convection as a dark spot of tungsten atoms that accumulate at the top of the bulb. That black smudge consists of tungsten atoms that didn't return to the filament and were swept upward as the hot argon and nitrogen gases rose.
However, some premium light bulbs contain krypton gas rather than argon gas. Like argon, krypton's is chemically inert. But a krypton atom is more massive than an argon atom, making it more effective at bouncing tungsten atoms back towards the filament after they sublime. Krypton gas is also a poorer conductor of heat than argon gas, so that it allows the filament to convert its power more efficiently into visible light. Unfortunately, krypton is a rare constituent of our atmosphere and very expensive. That's why it's only used in premium light bulbs, together with some nitrogen gas.
Incidentally, the filament in many incandescent bulbs is treated with a small amount of a phosphorous-based ‘getter that reacts with any residual oxygen that may be in the bulb the first time the filament becomes hot. That's how the manufacturer ensures that there will be no oxygen in the bulb for the tungsten filament to react with.
TTTH YETI 31 123
44 C
Jain Education International
For Private & Personal Use Only
www.jainelibrary.org
| SR No. | 524618 |
| Book Title | Tulsi Prajna 2004 01 |
| Original Sutra Author | N/A |
| Author | Shanta Jain, Jagatram Bhattacharya |
| Publisher | Jain Vishva Bharati |
| Publication Year | 2004 |
| Total Pages | 114 |
| Language | Hindi |
| Classification | Magazine, India_Tulsi Prajna, & India |
| File Size | 6 MB |