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== Resistance changes with temperature. The lamp becomes hotter, resistance changes. == An incandescent light-bulb takes just enough electric current to make a piece of metal glow brightly enough to give out visible light yet not get so hot that it melts and breaks. The piece of metal is called a tungsten filament. Experiments were made with different materials to use as the filament, including natural fibers, pure metals and alloys of different metals, to find the material which had the longest life whilst glowing brightly enough to give out visible light. The metal Tungsten was found to be the best. Also experiments were made trying a vacuum or different kinds of gas inside the glass bulb to find out which was the best. For many years Nitrogen gas was found to be the best but other gases or mixtures of gases may now be used. Fluorescent light bulbs electrically charge a gas (sometimes one of the inert gases like neon). Whilst it is normal every-day talk to say that a light bulb or a lamp is "burning", that is not strictly accurate because, speaking strictly scientifically, the word "burning" has a very precise meaning. When something is said to be "burning" it means the material is combining with the element Oxygen to form a compound called an Oxide. For example when Carbon is burnt it makes either Carbon Monoxide or Carbon Dioxide or a mixture of those two gases. How much of each is made depends on the actual conditions in which the Carbon is being burnt. That is why it is scientifically correct to say that a light bulb is "glowing" and not that it is "burning". == == == Modern light bulbs don't hold a vacuum. Instead they are filled with an inert (electrically non-conducting) gas such as Nitrogen. An inert gas is used to fill the bulb (instead of just pumping out almost all the air to leave a near-vacuum) because the action of filling the bulb with an inert gas can be used to flush away ALL of the air. In addition the inert gas has the very useful physical property of helping to conduct heat from the glowing filament to the glass bulb. This allows the whole surface area of the glass bulb to radiate heat into the surrounding air. It is important to understand that the inert gas does not allow the filament to "burn away", it just allows it to glow brightly. If some air were still present in the bulb - as sometimes happens if a light bulb gets knocked and gets even a tiny crack in its glass bulb - then the oxygen present in ordinary air will quickly make the filament burn away. If the light bulb just held a vacuum (as was the case in the early days of electric lighting) the main way the heat from the hot glowing filament could get out was along the wires feeding current to the filament and also along the insulators which support the filament. (Less heat passes through a vacuum compared with the flow of heat that can pass through an inert gas.) So the feed wires and insulators got very much hotter compared to the temperature they reach in modern light bulbs. This caused the old vacuum light bulbs, which glowed at a much higher temperature than radio tubes, to have a much shorter useful life compared to vacuum radio tubes. Re the answer given below, if the filament really was made from a material that has a negativetemperature coefficient (as temperature increases, resistance decreases) then the decreasing resistance would cause more and more current to be taken as the lamp heated up and the temperature would get higher and higher in a runaway manner until either the power supply's breaker would trip or (more likely) the light bulb's filament would simply explode! In fact the filament has to be made from a material that has a positive temperature coefficient. (As temperature increases, resistance increases.) Then, as the bulb's temperature rises, its filament's increasing resistance causes less current to be taken than when it was cold. Quite quickly a stable "steady-state" temperature and "running" resistance is reached so that the bulb simply continues to give out a steady amount of light according to the current it is taking from the electricity supply. == ==

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15y ago
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11y ago

The resistance of tungsten (used to manufacture incandescent lamp filaments) increases 15-20 times as its temperature increases to its hot operating temperature. This is because of the value of its temperature coefficient of resistance.

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12y ago

A hot filament emits electrons.Hence it indirectly changes the resistance.

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Q: How does a hot filament lamp affect resistance?
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Why does a filament lamp get hot when you use high voltage?

because there is a correlation between resistance and voltage and current. The equation resistance = voltage divided by current shows that the higher the voltage, the bigger the resistance,, and the bigger the resistance the hotter the filament lamp will get because of the electrons bumping into each other which means there is a loss of energy and that energy is being transferred to the filament making the actual filament bulb hot since there is more thermal energy wasted at the end.


WhY does a filament lamp get when you us high voltage?

because there is a correlation between resistance and voltage and current. The equation resistance = voltage divided by current shows that the higher the voltage, the bigger the resistance,, and the bigger the resistance the hotter the filament lamp will get because of the electrons bumping into each other which means there is a loss of energy and that energy is being transferred to the filament making the actual filament bulb hot since there is more thermal energy wasted at the end.


What is meant by cold resistance of filament lamp?

It means exactly what it sounds like. The resistance of an incandescent bulb's filament depends on its temperature. A filament has a positive temperature coefficient, which means that its resistance increases as its temperature increases. A typical 40 watt bulb (120 volts) has a cold resistance of about 28 ohms, but its hot, operating resistance is about 360 ohms. If the cold resistance were constant, the bulb would dissipate 379 watts. In fact, cold turn on is the most stressful time for a bulb.


What type of light build glows when a filament inside it gets hot?

Electric lamps having incandescent filaments.


When the filament in an incandescent lamp gets hot what kind off radiation does it give off?

the lamp gets hot


What is the current when a 60W lampis connected to 120v?

Since power is volts time amps, the current in a 60W lamp connected to 120V is 0.5A. Since a lamp is a resistive load, there is no need to consider power factor and phase angle, so that simplifies the explanation. ======================== Assuming this is an incandescent or halogen lamp (using a filament to make the light) there is a trick here: the resistance of a lamp filament varies with temperature and does not follow Ohm's law. The resistance will be much lower, thus the current will be much higher when the filament is cold, when the lamp is first connected. As the filament heats up, the resistance increases until it gets to a steady operating point of 0.5A. For a halogen lamp, the operating temperature is about 2800-3400K, so the R at room temperature is about 16 times lower than when hot... so when connected, the current is about 8A but drops rapidly. The current could be even higher if the lamp is in a cold environment. Non-halogen lamps operate at a lower temperature and would have a lower initial current--about 5A. And this all assumes the lamp is rated for 120V. If it is a 12V/60W lamp, the filament will probably break and create an arc, which may draw a very large current.


Is the resistance lower if you have a high current?

Lower than what? For the same voltage, a lower resistance means higher current. But beware, the voltage itself might depend on the current - thus - with a fixed resistance if you change the voltage, you will increase the current in the same proportion. Some things become higher resistance if they get hot (a tungsten filament in a lamp). Other things become lower resistance if they get hot (semiconductors). So it can all depend on what kind of circuit you have.


Does the resistance of a light bulb filament change after the light has been turned on?

The electrical resistance of a light bulb increases when it is turned on As a resistor, the tungsten light bulb has a positive resistance coefficient. This means that the electrical resistance goes up when the filament becomes hot. For example, a 100 watt light bulb operated at 120 volts - it does not matter if it is AC or DC for this calculation - will have a resistance of 144 ohms when hot and draw .833 ampere. When cold the filament typically has a resistance of only 10 ohms which increases as the filament heats up.


I need to draw a circuit diagram to show this but I have no idea how do you find the resistance of a lamp in a circuit?

If you have a lamp, you can assume that the resistance of the lamp when it is under power will follow the ohms law. BUT, one thing you must remember is, when a lamp is under load, it is glowing HOT. When metal is HOT, the molculoes of the meals are in much more active state. When this happens, the resistance will increase. Conversely, when the lamp is NOT on ON state, the filaments are cold. Moleculoes in the filaments are not as active. Thus, the resistance is lower. There is almost 10 to 1 difference in resistance from hot to cold. Taking out a multimeter and measuring the resistance of the lamp will not help you determine the resistance of the lamp when it is actually under load (with voltage applied) Really, the only thing you can do is to measure the voltage, measure the current, then arrive at the resistance mathmatically.


Why is a halogen lamp hot?

The halogen bulb produces a plasma arc on the inside of its quartz filament. Plasma glows at thousands of degrees. That's why they are hot.


Does the glow of bulb depend on current or voltage?

Since the bulb has a constant resistance, increasing the voltage will increase the current which will increase the brightness until the bulb blows in a flash of light.Ohm's Law governs this process where Volts = Current x Resistance.Another Answer Incandescent lamps do not have a constant resistance, as their resistance increases significantly with temperature. In fact, the 'hot resistance' of a lamp filament is around 10-18 times higher than its 'cold resistance'. The temperature increase, of course, is due to the current passing through the filament. This means incandescent lamps do notobey Ohm's Law and are, thus described as being 'non-ohmic' or 'non-linear'. However, to answer your question directly, the rated power of a lamp only occurs at the lamp's ratedvoltage. Even a small reduction in voltage will result in a significant loss of power and, thus, brightness. So, in this sense, a lamp's brightness is determined by the voltage applied across its filament.


What is the function of ignitor?

To provide a strong ,hot enough arc to light the lamp by over comingthe resistance of the gas in lamp.