The resistance of tungsten wire has a direct and significant effect on the brightness of the bulb. The following is a detailed analysis of this effect:
- The relationship between resistance and power
When the voltage is constant, the actual power of the bulb is inversely proportional to its resistance. This is derived from the calculation formula of electric power P=U²/R, where P represents power, U represents voltage, and R represents resistance. Therefore, when the voltage U remains constant, the larger the resistance R, the smaller the power P; conversely, the smaller the resistance R, the larger the power P.
- The relationship between power and brightness
The brightness of a bulb is determined by its actual power. The greater the power, the brighter the light emitted by the bulb; the smaller the power, the dimmer the light emitted by the bulb. Therefore, changes in resistance will directly affect the brightness of the bulb.
- The effect of tungsten wire resistance on brightness
The thinning of tungsten wire leads to increased resistance: As the bulb is used for a longer time, the tungsten wire will gradually sublimate and become thinner due to the thermal effect of the current. After the tungsten wire becomes thinner, its resistance will increase, resulting in a decrease in power, which will make the bulb dimmer.
Difference in tungsten wire resistance of bulbs of different powers: Observing bulbs of different powers, it can be found that the tungsten wires of bulbs with lower power (such as 25W) are usually thinner and longer, so their resistance is larger; while the tungsten wires of bulbs with higher power (such as 100W) are thicker and shorter, so their resistance is smaller. This also explains why bulbs of different powers have different brightness at the same voltage.
- Considerations in practical applications
During the design and manufacturing process of bulbs, manufacturers will adjust the length, thickness and material of tungsten wires according to the required brightness to control the resistance and power of the bulbs. In addition, in order to extend the service life of the bulbs and improve their luminous efficiency, manufacturers will also take a series of measures to reduce the sublimation and deformation of tungsten wires.
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