Why do you use tungsten filament for the filament of electric lamp? What are the characteristics of tungsten wire?

The main reason why tungsten is used in light bulbs is that it has the characteristics of high melting point and high resistivity, and is more durable than any other metal. These characteristics make it more suitable for light bulbs, because the filament needs to be able to withstand enough heat to emit light, but it can't break in the process.

High melting point of tungsten A good reason to use tungsten in incandescent bulbs is that it has a very high melting point. The melting point of tungsten is about 3400°C, which is much higher than the actual temperature of the bulb. This also makes tungsten the highest melting point metal.

Incandescent light bulbs usually reach 260 C? When the temperature is around 100℃, it reaches its peak. However, this temperature is obtained from the glass bulb around the filament, and the temperature of the filament itself is about 2500℃

This is the main reason for using tungsten, because in order to make light bulbs by using the heating principle, we obviously need something that can withstand such high temperatures. However, it is not enough to use it only once, and it needs to last longer, which many other metals can't do at all.

Another reason why tungsten with high resistivity becomes a high-quality bulb filament is that it has quite high resistivity. Resistivity more or less means its resistance to current. If the resistivity of the material is low, it means that electrons can pass more easily, while if the resistivity of the material is high, it is more difficult for electrons to pass.

In most designs, it is beneficial for materials to have low resistivity, because we can let more current pass through them when using the same volume of materials. It is for this reason that copper is the most commonly used material for electric wires. Because it has a relatively low resistivity and is cheaper than other good conductors (such as gold or silver).

However, in applications such as light bulbs, high resistivity is more advantageous. In most cases, this is because a certain resistance is needed in the circuit to make the required current pass through the circuit.

In order to understand this better, we first need to study what happens when a large number of electrons pass through the material. When an electron moves from point A to point B in a material, it will generate slight heat. You can think in terms of how exercise generates heat in physics.

The more electrons pass through, the more this effect will be amplified. This is not only because it will produce more motion in the material, but also because the electrons themselves will eventually start to compete for physical space. As you can imagine, it's like 100 people going through a door. Because there are too many electrons, they will start to compete for space.

This is also the reason why the conductor area becomes important, because the larger the area, the less electrons need to compete. This is equivalent to adding wider or more doors to the metaphor of 100 people. Having said that, the greater the resistance given to electrons, the more work they need to pass through the material. Higher resistance will also lead to increased heating.

Once we understand this, we can begin to understand how tungsten wire shines in a light bulb.

The actual wire as a filament is very thin, which is a very narrow path for electrons to pass through. This will create a huge resistance in the filament, which will lead to the accumulation of heat and eventually lead to light emission. As mentioned earlier, in order to produce this glow, we need to reach a very high temperature. That's why tungsten is very suitable for this purpose, because it can't be melted at the temperature needed to emit light.

The evaporation of tungsten is low. When we create something that runs at such a high temperature, we begin to encounter the problem of things evaporating. Although tungsten has a high tolerance to high temperature, it will damage the filament at the microscopic level.

If the change occurs in such a small range, it is acceptable. The damage is due to the passage of electrons, and tungsten will start to vibrate. These vibrations will cause a single atom to split from the rest of the filament and eventually land on the glass of the bulb.

This will not only weaken the filament due to mass loss, but also start to affect the light output of the bulb, because there will be a small layer of tungsten inside the whole glass bulb. Their solution to this problem is to start filling the bulb with inert gas. Before that, they used to vacuum the inside of the light bulb to prevent any form of combustion between huge heat and oxygen.

They did this because the light bulb wouldn't burn without oxygen, so they decided to use a vacuum to prevent this from happening. However, gas can also be put into the bulb, but it is important to pay attention to which gas is chosen for this purpose. Most gases burn like oxygen, which is why inert gases must be used instead.

Due to the nature of these types of gases, inert gases do not react chemically with heat, which is why it was decided to use this gas in the bulb. The most commonly used gas in these bulbs is argon.

The effect of filling the bulb with glass is quite simple, but it is very effective. Its function is to provide something for the separated tungsten atoms to rebound, rather than directly shooting at the glass bulb.

If we give tungsten something to bounce back, it will probably bounce back to the filament again. This will cause the atoms to recombine with the filament and continue to work as before.

abstract

After many experiments, people finally found that tungsten is more effective than any other metal. In contrast, other metals are ignored.