08.18.2018: One Chapter of Nonfiction


Today's soundtrack is Society's Finest: The Journey So Far.


This morning, I'm reading the sixteenth chapter of The Cartoon Guide to Physics by Larry Gonick and Art Huffman.


If we take a battery, put a wire on its positive side, connect that to a light bulb, connect that light bulb to another light bulb, and connect that second light bulb to a third light bulb, then connect that last lightbulb to the negative side of the battery, we call this being wired in series. All three light bulbs will get power from the same battery. All three lights will get the same amount of power, since charge "doesn't accumulate in the circuit" (p. 143); however, each light bulb will only get a third of the power that a lone bulb would have gotten, because the resistance is tripled.


The "loop theorem," Kirchhoff's first law, tells us that the lamps will use all of the energy that the battery releases. Interestingly, if three bulbs are connected in series, because "power is voltage times current, each bulb is one ninth as bright as one bulb connected alone" (p. 144). If we connect two bulbs in series that are different watts, the bulb with the lower watts will be brighter than the bulb with the higher watts, because the lower-watt bulb has more resistance, so it gets more voltage.


The other way to wire multiple items together with one power source is to connect in parallel. To do so, we connect one long wire to the battery's positive terminal, and another to its negative terminal. Then we can put light bulbs in-between the two wires, using two short wires on each side of each light bulb: one to connect it to the long positive wire; the other to connect it to the long negative wire. This allows all of the batteries to shine just as brightly as they would have even if there were no other batteries connected to the circuit, because of Kirchhoff's second law, which tells us that the same energy that goes into a circuit will come back out of a circuit, due to the fact that "the flow of charge [...] is conserved" (p. 146). We can determine how much energy is going to each bulb in parallel by "Ohm's law: i=v/r" (p. 146), which tells us that its current (i) is equal to voltage divided by resistance.

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