[noob] Resistance in paralel = increase in current?

Hi, I'm following a book here and it was talking about resistance and how to calculate the total resistance of a circuit. I understand everything pretty well except the part that said something like: now having another resistance connected in paralel to the initial resistance, the current will double and go in both resistance... it also says something like the battery is producing more current because of this.

I'm wondering, is this true? I don't have a multimeter (yet) to verify... would an ammeter show an increase of current in this circuit? And as I understand it, having a circuit in paralel is just a great way of depleting a battery's power faster! (Oh i'm sure there are good applications for this, i'm not there yet)

But also, can you explain what happens with the current and why it increases when a paralel resistance is added?

Thanks a lot! Simon

Reply to
Simon
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A resistance in parallel with another resistance is an additional path for current to flow. Given a fixed voltage, more paths (less resistance) means more current flow. You might want to search on "conductance," which is another way of understanding this phenomenon.

Reply to
Charles Schuler

Yes - this is true.

The battery voltage will stay the same when you add a second resistor (or close enough for this discussion), so you can consider each resistor (each parallel branch of the circuit) independently.

If you have, for example, a 10 volt battery, and two 10 ohm resistors connected in parallel across it, each resistor will draw 1 amp (10volts/10 ohms), so the total current delivered by the battery will be 2 amps.

In house wiring, all the lights and outlets are connected in parallel across the 120V (in North America) or 240V (elsewhere) AC supply. Likewise, in a car, all the lights, radio, starter, etc. are connected in parallel across the 12 volt battery. In either case, each light or other load draws what it wants from the power source, and the power source therefore delivers the total of all currents demanded by the loads.

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Reply to
Peter Bennett

That statement makes the assumption that the voltage across the two resistors in parallel is the same as the voltage across the original resistor and the second resistor is similar to the first one.

You open the door of a car and the dome light comes on (is connected across the battery. The battery generates enough current to light that bulb. You leave the door open, and turn the headlights on. The battery now also generates enough current to light those bulbs (that are connected in parallel with the dome light). Those bulbs are resistors. Actually, you may notice the dome light dims, slightly, when you turn the headlights on, because the battery will not hold a perfectly steady voltage as it generates the higher current. It has a little effective internal resistance that is in series with those two sets of lights that are in parallel with each other. The real world is complicated. Sorry.

The second resistor forms a second circuit (path for current) that is sort of beside the first path. The current through the first resistor is little changed by this second path, if the battery has a low internal resistance compared to each of these two resistors.

Exactly so, but sometimes you need a power source to do two things for you, at the same time.

Have you ever seen a Y connector to put on a water faucet so you can connect two hoses? Running water through one hose lets less water out of the faucet than running water from two of them at, the same time.

Reply to
John Popelish

"Simon" wrote in news:1176419553.120433.269350 @l77g2000hsb.googlegroups.com:

*snip*

*snip*

Christmas lights. When one bulb burns out, the strand stays light. (Hm... 300 lightbulbs come on at once when the OP understands this. ;-))

Puckdropper

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Reply to
Puckdropper

Yes, as others have said.

Yes.

Sure you are, you just don't know it. You've seen it hundreds of times. For example a car's headlights are in parallel, the 120 volt electrical devices in your house are in parallel, the clock in a clock radio is in parallel with the radio, and so forth.

That has already been explained, but I'll add another way of thinking about it. Say you have a light bulb lighting an area. You want to make it brighter, so you add another bulb, and now it's twice as bright. That means twice as much electrical energy needs to be consumed That's why the current increases - you are using twice as much energy.

In mathematical terms, E = I * R where E is voltage, I is current and R is resistance. When E is a constant voltage, say a 12 volt battery, and you decrease R, I must rise. Say you have a 12 volt battery connected to a 12 ohm resistor. E=I*R, so I must equal 1 amp. Now, you add a second 12 ohm resistor in parallel with the first. The paralle resistance equals 6 ohms, so 12 = I * 6 which means I is 2. Each resistor will have 1 amp through it, making 2 amps total.

Ed

Reply to
ehsjr

if you parallel two equal resistances the total resistance is half, current equals voltage devided by the resistance, so when the resistance is cut in half the current doubles. Also in a series circuit you have the same current everywhere but different voltage drops relative to the resistance of each component, while in a parallel circuit you have the same voltage in each branch but different amounts of current according to the resistance of the branch.

Reply to
Randy

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