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I know that in parallel circuits, the battery, or other power source is supposed to provide the necessary amount of voltage to each resistor in the circuit. I also know that unplugging or turning on or any other action done to one resistor in a parallel circuit will not affect the other resistors. That said, I was wondering why when I plug in my hairdryer, the light in my room dims. Isn't this a violation of the laws relating to parallel circuits?
Question Date: 2006-04-04
Answer 1:

This is a frequent question that people ask at home, especially in third world countries, where the sources of energy are not as efficient as in more developed places.

What you say in your question is correct only about the voltage, but you forgot to consider the role of the current. Once you apply any voltage to a resistor, a current flows through it. When you plug in your hairdryer, you are demanding more current to the main source apart from the one provided to the light; the source has a limited supply. Sometimes we just plug in so many devices, that our electrical system cannot drive them well.

There are devices called current regulators and they compensate for changes in the load. We call the load to any device that you plug in, like your hairdryer. Most electrical systems at home are designed with those regulators, but if you plug in several things at the same time, your demand of electricity might not be satisfied by the source, in spite of the regulator.

I hope it helps.

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