# Two Qs re: resistance

1. ## Two Qs re: resistance

Not sure if the answer depends on the circuit, or if this is a rule that will apply across the board?

So, I get that a resistor will limit the flow of current in the circuit.

I have a circuit with a 10k resistor, and let's say I add to that a 4.7k resistor. I believe this to be called 'piggybacking'?

1. Is that considered series, or parallel?

2. Why is the amount of current now decreased? To my complete newbie brain, there should be more resistance; to me, there is now 14.7k of resistance (+ or - a bit, due to tolerance). But apparently, there is now 5.3k of resistance. Why is that?

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2. ## Re: Two Qs re: resistance

If the two resistors have one terminal in common, then it is series connection and current will reduce if the voltage across the series connection stays the same as it was when only one resistor was connected.
If the two resistors have two terminals in common, then it is parallel connection and under the same circumstances as above, the current will increase.

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3. ## Re: Two Qs re: resistance

Where did you get 5.3k? Resistance of parallel circuit is 10*4.7/(10+4.7) = 3.2k.

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4. ## Re: Two Qs re: resistance

Originally Posted by sutapanaki
If the two resistors have one terminal in common, then it is series connection and current will reduce if the voltage across the series connection stays the same as it was when only one resistor was connected.
If the two resistors have two terminals in common, then it is parallel connection and under the same circumstances as above, the current will increase.
Ok, that helps.

Originally Posted by FvM
Where did you get 5.3k? Resistance of parallel circuit is 10*4.7/(10+4.7) = 3.2k.
Well, where I get 5.3 is this: 10k - 4.7k = 5.3k

But I see that's not the way it works. :)

Thanks guys!

5. ## Re: Two Qs re: resistance

I have a circuit with a 10k resistor, and let's say I add to that a 4.7k resistor. I believe this to be called 'piggybacking'?
Each resistor has two ends. It is a symmetrical device in the sense that you can exchange the two ends without ANY effect.

Let us label the two ends of resistor R1 as E1 and E2. Same way label the two ends of resistor R2 as E3 and E4.

If you connect E2 to E3 and keep the two free ends E1 and E4, you get s series connection. In a series connection, both resistors takes the same current (consider current like a fluid).

If you connect E1 to E3 and also connect (independently) E2 to E4, and use the two ends (E1E3 junction and E2E4 junction) you get a combination that is called parallel (the two resistors are now lying side by side).

In a parallel connection, both the resistors see the same voltage (but take different currents).

In a series connection, the equivalent resistance is greater than the individual values. In a parallel connection, the equivalent resistance is smaller than the individual values.

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