how does a bulb light up?

Question

plz tell me the entire working of its components as well,filaments,abt the resistances in them as well.

Answer 1

The incandescent light bulb consists of a glass enclosure (the "envelope") which either contains a vacuum or is filled with a low-pressure noble gas. Irving Langmuir found that filling the bulb with an inert gas reduces evaporation of the filament and reduces the required strength of the glass. Inside of the bulb is a filament of tungsten wire, through which an electrical current is passed. As the electrons that travel through the filament bump into the atoms, some of the electrons in the atom may become excited. This means they temporarily boost its energy level and raise to higher orbit. When they fall back, energy is released as photons, a photon being the particle form of light. A great deal of lower-energy electromagnetic radiation is released as infrared as well—more, in fact, than is released as visible light. This manifests as heat.

Incandescent light bulbs usually also contain a glass mount on the inside, which supports the filament and allows the electrical contacts to run through the envelope without gas/air leaks. Many arrangements of electrical contacts are used, such as a screw base (one or more contacts at the tip, one at the shell), a bayonet base (one or more contacts on the base, shell used as a contact or only used as a mechanical support), and for some lamps an electrical contact at either end of a tubular lamp. Contacts in the lamp socket allow the electrical current to pass through the filament. Power ratings range from about 0.1 watt to about 10,000 watts.

To improve the efficacy of the lamp, the filament usually consists of coils of fine wire. For a 60 watt 120-volt lamp, the length of the filament is usually 2 meters or 6.5 feet.

One of the major problems of the standard electric light bulb is evaporation of the filament. The inevitable variations in resistivity along the filament cause non-uniform heating, with "hot spots" forming at points of higher resistivity. Thinning by evaporation increases resistivity. But hot spots evaporate faster, increasing their resistivity faster—a positive feedback which ends in the familiar tiny gap in an otherwise healthy-looking filament. Irving Langmuir suggested that an inert gas, instead of vacuum, would retard evaporation and still avoid combustion, and so ordinary incandescent light bulbs are now filled with nitrogen, argon, or krypton. However, a filament breaking in a gas-filled bulb can pull an electric arc, which may spread between the terminals and cause very heavy current flow; intentionally thin lead-in wires or more elaborate protection devices are therefore often used as fuses built into the light bulb.

During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of 750-1000 hours for ordinary lamps. See the section below, Voltage, light output, and life, for a discussion of the trade-offs involved in setting a lamp life specification.

In a conventional (not halogen) lamp, the evaporated tungsten eventually condenses on the inner surface of the glass envelope, darkening it. For bulbs that contain a vacuum, the darkening is uniform across the entire surface of the envelope. When a filling of inert gas is used, the evaporated tungsten is carried in the thermal convection currents of the gas, depositing preferentially on the uppermost part of the envelope and blackening just that portion of the envelope.

Some old, high-powered lamps used in theatre, projection, searchlight, and lighthouse service with heavy, sturdy filaments contained loose tungsten powder within the envelope. From time to time, the operator would remove the bulb and shake it, allowing the tungsten powder to scrub off most of the tungsten that had condensed on the interior of the envelope, removing the blackening and brightening the lamp again.

Answer 2

The filament in an incandescent bulb is a poor conductor (or good resistor, depending on your perspective). The result of forcing electricity (forcing electrons to flow) through a poor conductor is friction between the filament's atoms and the electrons, which results in heat, which causes the filament to glow which we see as light.

Answer 3

Yes, bulbs with a filament are lit by heat, so much that the resistance of the special metal, causes it to glow. Other bulbs like flouresent(long tube lights) use a high voltage to induce a gas to glow.

Answer 4

the filament is a low resistance heater, basically. Electricity passing through the filament causes it to heat up, heating the gases inside the bulb, causing them to glow

Answer 5

in bulb tontung is used.as a heating component when electric energy is converted to heat energy the tontung is red hot glow it gives light that's all.it can be measure in watt.

Answer 6

Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called light photons, are the most basic units of light. (For more information, see How Light Works.)

Atoms release light photons when their electrons become excited. If you've read How Atoms Work, then you know that electrons are the negatively charged particles that move around an atom's nucleus (which has a net positive charge). An atom's electrons have different levels of energy, depending on several factors, including their speed and distance from the nucleus. Electrons of different energy levels occupy different orbitals. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus. When an atom gains or loses energy, the change is expressed by the movement of electrons. When something passes energy on to an atom, an electron may be temporarily boosted to a higher orbital (farther away from the nucleus). The electron only holds this position for a tiny fraction of a second; almost immediately, it is drawn back toward the nucleus, to its original orbital. As it returns to its original orbital, the electron releases the extra energy in the form of a photon, in some cases a light photon.
The wavelength of the emitted light (which determines its color) depends on how much energy is released, which depends on the particular position of the electron. Consequently, different sorts of atoms will release different sorts of light photons. In other words, the color of the light is determined by what kind of atom is excited.

This is the basic mechanism at work in nearly all light sources. The main difference between these sources is the process of exciting the atoms.

Light bulbs have a very simple structure. At the base, they have two metal contacts, which connect to the ends of an electrical circuit. The metal contacts are attached to two stiff wires, which are attached to a thin metal filament. The filament sits in the middle of the bulb, held up by a glass mount. The wires and the filament are housed in a glass bulb, which is filled with an inert gas, such as argon.

When the bulb is hooked up to a power supply, an electric current flows from one contact to the other, through the wires and the filament. Electric current in a solid conductor is the mass movement of free electrons (electrons that are not tightly bound to an atom) from a negatively charged area to a positively charged area.

As the electrons zip along through the filament, they are constantly bumping into the atoms that make up the filament. The energy of each impact vibrates an atom -- in other words, the current heats the atoms up. A thinner conductor heats up more easily than a thicker conductor because it is more resistant to the movement of electrons.

Bound electrons in the vibrating atoms may be boosted temporarily to a higher energy level. When they fall back to their normal levels, the electrons release the extra energy in the form of photons. Metal atoms release mostly infrared light photons, which are invisible to the human eye. But if they are heated to a high enough level -- around 4,000 degrees Fahrenheit (2,200 degrees C) in the case of a light bulb -- they will emit a good deal of visible light.

The filament in a light bulb is made of a long, incredibly thin length of tungsten metal. In a typical 60-watt bulb, the tungsten filament is about 6.5 feet (2 meters) long but only one-hundredth of an inch thick. The tungsten is arranged in a double coil in order to fit it all in a small space. That is, the filament is wound up to make one coil, and then this coil is wound to make a larger coil. In a 60-watt bulb, the coil is less than an inch long.

Tungsten is used in nearly all incandescent light bulbs because it is an ideal filament material. In the next section, we'll find out why this is, and we'll examine the role of the glass bulb and inert gas.

A metal must be heated to extreme temperatures before it will emit a useful amount of visible light. Most metals will actually melt before reaching such extreme temperatures -- the vibration will break apart the rigid structural bonds between the atoms so that the material becomes a liquid. Light bulbs are manufactured with tungsten filaments because tungsten has an abnormally high melting temperature.
But tungsten will catch on fire at such high temperatures, if the conditions are right. Combustion is caused by a reaction between two chemicals, which is set off when one of the chemicals has reached its ignition temperature. On Earth, combustion is usually a reaction between oxygen in the atmosphere and some heated material, but other combinations of chemicals will combust as well.

The filament in a light bulb is housed in a sealed, oxygen-free chamber to prevent combustion. In the first light bulbs, all the air was sucked out of the bulb to create a near vacuum -- an area with no matter in it. Since there wasn't any gaseous matter present (or hardly any), the material could not combust.

The problem with this approach was the evaporation of the tungsten atoms. At such extreme temperatures, the occasional tungsten atom vibrates enough to detach from the atoms around it and flies into the air. In a vacuum bulb, free tungsten atoms shoot out in a straight line and collect on the inside of the glass. As more and more atoms evaporate, the filament starts to disintegrate, and the glass starts to get darker. This reduces the life of the bulb considerably.

In a modern light bulb, inert gases, typically argon, greatly reduce this loss of tungsten. When a tungsten atom evaporates, chances are it will collide with an argon atom and bounce right back toward the filament, where it will rejoin the solid structure. Since inert gases normally don't react with other elements, there is no chance of the elements combining in a combustion reaction.

Cheap, effective and easy-to-use, the light bulb has proved a monstrous success. It is still the most popular method of bringing light indoors and extending the day after sundown. But by all indications, it will eventually give way to more advanced technologies, because it isn't very efficient.

Incandescent light bulbs give off most of their energy in the form of heat-carrying infrared light photons -- only about 10 percent of the light produced is in the visible spectrum. This wastes a lot of electricity. Cool light sources, such as fluorescent lamps and LEDs, don't waste a lot of energy generating heat -- they give off mostly visible light. For this reason, they are slowly edging out the old reliable light bulb.

Answer 7

i did this in science class in 4th grade but um i guess the filiments are connected to a wire which are connected to the electrictiy area and when they touch, the electricity goes back up the wire and touches teh glass bead inside, which causes the light bulb to light up. i guess.........................................

Answer 8

my frnd... did you do physics in class 10 ?