UCSB Science Line
 So, my students have been working with DC power supplies testing different types of circuits. While doing this we noticed something unusual while connecting two light bulbs in series. Yes, the current is lower than it would be for a single bulb and yes the bulbs are dimmer but they are not equally bright. In fact, one (the first one electrons are passing through) is probably four times as bright. This happened with every single class and every single apparatus. What's up? Question Date: 2013-04-13 Answer 1:There could be mismatched brightness if the bulb resistances do not match. Because they are in series the current is the same in each bulb, but if one bulb has a higher resistance it gets hotter since P=I*V=I2*R and hotter means brighter. The teacher should get a multimeter and measure bulb resistance. They should also check if the same bulb is brighter no matter if it is the 1st or 2nd bulb. There could also be something weird going on with their setup, if there are pictures I can take a look. Click Here to return to the search form.