Interested to Buy Any Domain ? << Click Here >> for more details...
In a incandescent bulb, if the glass is punctured, and then
power is supplied, the tungsten filament blows up with a
flash.Why?
- 2 Answers
- 5376 Views
- I also Faced
- E-Mail Answers
Answer Posted / nagarajan
Gases used for filling incandescent lamps must be chemically
inert, i.e. they should not react with the hot filament
(with the exception of halogen lamps). This means that they
also need to be extremely pure, as very small amounts of
some substances can have disastrous effects. For example, a
single drop of water in a gas cylinder capable of filling
half a million GLS lamps would cause every one of those
lamps to blacken and fail early! The following table shows
the gases that are inert to tungsten and make suitable
fillings:
Gas Symbol Molecular Weight Thermal Conductivity % in
Atmosphere
Hydrogen H2 2 0.1805 N/A
Helium He 4 0.1513 0.0005
Neon Ne 20 0.0491 0.0015
Nitrogen N2 28 0.02583 78.03
Argon Ar 40 0.01772 0.94
Krypton Kr 84 0.00943 0.0001
Xenon Xe 131 0.00565 0.000009
The molecular weight is the weight of one atom or molecule
of the gas. The heavier atoms are more effective in reducing
filament evaporation, making the lamp last longer. It can be
seen that they also feature lower thermal conductivity,
reducing gas losses so the filament will run hotter and
produce light more efficiently.
Consequently for incandescent lamps it would appear that
xenon would be the best choice of fill gas. But this is only
present in very small quantities in the atmosphere, which
makes it expensive. Krypton is about ten times cheaper but
still too scarce, so we generally use argon which is roughly
500 times cheaper. However the first gas-filled lamps had to
use nitrogen, because at the turn of the century there were
no argon distillation factories in existence. When argon
lamps were eventually introduced, it was found that its
lower electrical ionisation potential resulted in problems
of arcing between the lead wires. This was overcome by the
admixture of a small amount of nitrogen, and an 85:15
argon:nitrogen mixture is common in European lamps. Lower
voltage American lamps can get away with a 95:5 gas and thus
are slightly more efficient. The fill pressure is about 0.8
atmospheres which normally rises to just above atmospheric
pressure when the lamp is in operation.
By the 1930s the price of krypton had reduced considerably
as new distillation plants were opened, and in 1936 Tungsram
of Hungary put the first krypton-filled GLS lamp on the
market. To reduce the required volume of this expensive gas,
a new glass bulb shape was designed. The result was a lamp
having a mushroom shaped envelope, which is still produced
today. The Krypton Mushroom lamps usually offer a
combination of about 5% more light and 50% longer life than
ordinary argon-filled bulbs. Alternatively an energy-saving
range of lamps producing the same light but with 10% lower
wattage is available. It is also standard practice to employ
krypton in high efficiency miniature lamps, because the
benefits of krypton are much more pronounced for lower
voltage types. Miner’s cap lamps are an important
application, since a smaller battery can provide the same
light level. Even xenon is sometimes found in today’s
miniature halogen capsules where a very high efficacy or
long life is called for, especially in automotive and
projection lamps.
The only other gas which has been commercially employed in
incandescent lamps is hydrogen. It is characterised by a
very high thermal conductivity making it inefficient for
general lighting, but it has been employed in special signal
lamps because it cools the filament more rapidly between
pulses. The faster nigrescence time permits higher speed
signalling by light pulses. The table below shows the main
applications of the available lamp filling gases:
Gas Type Applications
Hydrogen Rapid-Nigrescence lamps for high speed signalling
(obsolete).
Neon Low pressure sodium, Neon glow indicators, Linear Neon,
Penning-start sodium.
Nitrogen Very large incandescent, Studio Halogen, Mercury &
Metal Halide lamp outers.
Argon Incandescent, Halogen, Linear Fluorescent, Mercury and
Metal Halide arc tubes.
Krypton Small halogen, Krypton Miners, Special automotive,
Energy saving fluorescent.
Xenon High performance halogen, High pressure sodium arc
tube, Flashtubes, Xenon Arc.
| Is This Answer Correct ? | 5 Yes | 0 No |
Post New Answer View All Answers
why we have to particulary use ACB for below ratings,even available of MCB,MCCB with that range ?
Can any one provide the inspection procedure of MIMIC for VFD panel? Details: If someone wants to have a mimic in the VFD panel what are inputs considered for the mimic(like on,off,trip) whether we are able to add speed variation in the mimic(if so how can we get) and what are the parameters to be checked in the MIMIC during inspection?
what is the total power generation in india?
In a single how much maximum current and watts using
How to use earthing on shipments.
# 4 hi friends i m from electrical branch and seeking for tech. + apti. both papers of hpcl plz get it available as soon as possible my email id is sumit_lig189@yahoo.co.in
Why PT voltages are measured with respect to ground? What do u mean by voltage or current polarized.
An ELHNC 80amp 240v 30mA RCD is tripping periodically, every 30 - 180 seconds is it safe to disconnect the protection circuit?
IN SINGLE PH TRANSFORMER IF LEKAGE IMPEDANCE DROP IS NEGLECTED ,THE FLUX IN THE MAGNETIC CORE and the lekage flux linking a winding are a)proportional to the applied v to the winding i respectively.
How to checked frequency drive output voltages?
WILL SCHNEIDER MAKE ACB(MASTERPACT)TRIP ON REVERSE POWER?
what is proper capacitor placement? How to evaluate capacitor size?
please send me privious exam's queation papers of section engineer(electrical).
how does the terminal voltage of transmission lines increase when a capacitor is connected???? This happens not only in transmission lines but also in all circuits. How??? When a capacitor is connected in a transmission line, capacitor also takes energy from the same supply. But how is it able to increase the terminal voltage??? Practically What sequence of events happen during increase in voltage???
What is the maximum No. of out going mccbs permitted from an LV distribution paqnel? What is the ampere relation between incomer and out going switch gears/mccbs?
