is it safe to connect an electric bulb rated 40-200 watt to a line voltage of 300
Answers
Answer:You can not calculate this like if it was a resistor. The filament in light bulb change resistance with temperature.
Here is the only case that work:
When the voltage is too high for a light bulb, it is no problem to connect many light bulb in series, all the same model (same voltage, same piwer in watts, same current).. Christmas lights, for example ; 10 light bulb of 12 volt in series works fine. Even car healight, 10 of these in series, normally using 5 amps at 12 volt would take 5 amps under 120 volt ac.
However, if any of the 12 head light would be unequal, for example connected on high beam filament, then the non linear resistance of tungsten would become evident.
Example 1: 11 head light on low beam, 1 on high beam:
The 11 head lights would be brighter than usual and the voltage on each one would be around 13 volt. Its ok because they are designed to work at 14.4 volt, the voltage needed to charge a lead/acid battery.
The only head light on high beam would be dimmer and the voltage would be about 2 volt.
Example 2: 11 head lights on high beam and one on low beam, all connected in series and powered on 120 volt ac.
Result: the only head light on low beam would flash very bright for 1/60 second and burn.
What happened?
Because on the non linearity, the light bulb which present the highest resistance on cold start immediately receive a higher voltage than all the other. It quickly reach full temperature, which makes it resistances raise by a factor of 15. The other light bulbs get less than 12 volt, so they slowly warm up and barely become dim red.
Because all the light bulb are connected in series, the current is identical. However, the voltage keep rising faster in the low beam bulb. It quickly reach the value that destroy the filement, for a low beam, the same current for high beam is only making then dim, no worry, no stress for those 11 head light.
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