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Most simple incandescent light bulbs are made of a thin section of tungsten through which the current flows.
This section of tungsten is called a "filament".
The tungsten filament has electrical resistance and so is a resistor.
As a resistor it develops a voltage drop. This voltage drop multiplied by the amperage passing through it equals the wattage of the bulb.
The heated tungsten gets to thousands of degrees above room temperature and becomes hot enough to produce yellow-white visible light.
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.
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DevinThe filament of a lamp is NOT an 'ohmic' resistor. It is, in fact, 'non-ohmic'.
The term, 'ohmic' (or 'linear'), to those materials that obey Ohm's Law. Materials that do not obey Ohm's Law are called 'non-ohmic' (or 'non-linear').
For Ohm's Law to apply, the ratio of voltage to current must remain constant for variations in voltage. This is not the case for tungsten, from which a lamp's filament is manufactured.
As the voltage across a tungsten filament is increased, the ratio of voltage to current changes -if you were to plot a graph, you would see a curve, rather than a straight line. This clearly confirms that tungsten does NOT obey Ohm's Law.
The incandescent light bulb sends electrical current through a Tungsten filiment which resist the flow of current (it is the resistor). This resistance generates heat and makes the filiment glow. Tungsten has an extremely high melting point so it makes a good filiment for a bulb as it can glow brightly for a long time before giving out.
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