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Re: But the Alternator Runs Anyway



At 12:05 PM 2/22/02 -0700, you wrote:

In one of the conceptual physics textbooks, the question asked was
whether there was a greater consumption of gas in a car while the engine
was running if the car lights were left on. As obvious as the answer
seemed, I responded, yes it would. The energy had to come from
somewhere. But one of my students reminded me that the alternator ran
all the same whether the lights were on or not; so the overall gas
consumption stayed the same; in his opinion, it did not make any
difference. What do you think?
- Abby
If you play with a small handheld generator that can power some small light
bulbs you will notice that it turns very easily when no bulbs are turned
on. However when several bulbs in parallel are on it is noticeably harder
to turn. Therefore even though the alternator is turning all the time it
will take more engine torque to turn it with the headlights on and thus the
engine will do more work on the alternator to run the headlights and the
gas consumption will definitely go up.




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Ivan Rouse, Physics Professor
Physics Department, La Sierra University
4700 Pierce St., Riverside, CA 92515
email: irouse@lasierra.edu
phone: 909-785-2137, FAX 909-785-2215

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