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How does the number of light bulbs in a series circuit affect the current that is going through the circuit?

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The more light bulbs you have in a series, the lower the current is. That is because the resistances of the light bulbs add. It is a bit more complicated than with linear resistors (two same resistors in a series have half of the current $I=\frac{U}{2R}$). It is because the resistance of the light bulb changes with the temperature (current) see wikipedia. For lower current, the resistance is lower. Therefore the current of two light bulbs is going to be less than the current of one light bulb but more than a half of one light bulb.

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  • $\begingroup$ Your answer assumes a constant voltage power supply. The majority of practical circuits are designed to be powered by batteries, or by the power grid, or by a voltage regulated power supply, all of which do a pretty good job of maintaining constant voltage; but not all circuits expect constant voltage. One modern example would be LED lighting circuits which often are powered by a constant current power supply. If you have LEDs in series powered by a constant current supply, then adding more LEDs does not change the current: It makes the voltage go up (to some limit, of course!) $\endgroup$ – Solomon Slow May 8 '17 at 14:26

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