3. After getting everything wrong last timeBob now asks for help when he\'s conf

Question

3. After getting everything wrong last timeBob now asks for help when he's confused. Help him become less confused by answering his questions below. Note: just because its Bob saying these things doesn't mean that theyre easy to answer. Think through each of them carefully! a) I don't understand how light bulbs can come on instantly after you flick the switch. Doesn't it take at least a second or two for the electrons to travel from the wall all the way up the wire into the light bulb?" b) I have two equations for electrical power: P = 12R and P = v2/R. The first one says bigger resistors will use more electrical powerbut the second one makes it looks like that the bigger resistor will use less power. One of them must be right: if I have a 100 and a 2002 resistor in a circuitwhich resistor is getting more power from the battery?

Explanation / Answer

a)

Consider how a train starts up. The train itself starts moving at one or two miles per hour. But the back of the train starts moving at almost the same time as the front. The impulse to start moving runs down the train far faster than the train itself starts moving.

In the case of electrons, the first electron moves a tiny bit - and pushes the next, which pushes the next, which pushes the next, all the way round the circuit from one pole of the generator to the other. The impulse to start moving travels at about half the speed of light, even though the individual electrons move at only feet per second.

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