# How in a series circuit do the components know how much of the electricity to use?

1. Apr 19, 2012

### MattA147

How in a series circuit do the components know how much of the "electricity" to use?

How does this happen? Why doesn't the first lamp in a series use all the volts? How does it know if there are any other lamps in the circuit? Any help would be greatly appreciated. :)

2. Apr 19, 2012

### tiny-tim

Hi MattA147!
Let's convert this is into a specific question …

suppose there's a 3 V battery and three 1 Ω resistors; two of the resistors are in series with the battery, and the third resistor is in series with a switch, and parallel to the second resistor …

when the switch is open, there's a voltage drop of 1.5 V across each of the two resistors, and a current of 1.5 A

when the switch is closed, there's a voltage drop of only 1 V across the first resistor, and a current of 2 A …

but when the switch first closes, how long does it take the battery to put an extra 0.5 A into the circuit, and why?

Now i'll let someone else answer that

3. Apr 19, 2012

### Staff: Mentor

Re: How in a series circuit do the components know how much of the "electricity" to u

A short excursion into Analogy Land:

How does a river know not to use up all of its water at the first waterfall?

Electricity is a flow of charges along a course that proceeds from a source at high potential and leads eventually ("downhill") to the lowest potential it can find -- that of the "return" of the source. Equal numbers of charges that leave the "top" of the source must return to the "bottom" of the source.

Every waterfall is only so high, and unless it drops straight into the ocean the water falling over it cannot lose all the potential energy that it has... it must continue to flow downhill and can "power" more waterfalls on its way to the sea.

The same is true for electricity fallowing a circuit. The potential that the charges have at any point in the circuit depend upon their location in the field that exists between the source's terminals and follows the wiring. Essentially the charges "flow downhill" until they "reach the bottom".