Resistor Question

[Monkey12]

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Anyone got Kap FL #3 #75 handy?
In the circuit (2 parallel resistors each R1=R2=10 Ohms) Removing R1 will have which of the following effects on the current through R2...
a. decrease to .5
b. no change
c. double
d. increase by a factor of 10

Taking out a parallel resistor would increase the total resistance so why wouldnt the current decrease? Their answer is B No change...But I don't see how this could be right...and instead they have *note the current through the battery will decrease by a half...can anyone explain please...

 

[antissa]

I haven't done this test but I remember reading about it in another thread
I think someone explained that taking out a resistor will increase the total resistance of the whole circuit, but it will not affect the current through the untouched resistor itself

 

[OHare]

The voltage across the resistor will never change, thus how can the current change? Even if you had a million equivalent resistors in parallel with that battery, they would all have the same voltage, thus the same current through them.

 

[Monkey12]

The voltage across the resistor will never change, thus how can the current change? Even if you had a million equivalent resistors in parallel with that battery, they would all have the same voltage, thus the same current through them.

But when you take out or add resistors doesn the whole picture change? I thought current could adapt based on the resistors in the circuit...Like if you added another resistor in series, you'd increase the overall resistance and the current would have to decrease?

 

[willthatsall]

But when you take out or add resistors doesn the whole picture change? I thought current could adapt based on the resistors in the circuit...Like if you added another resistor in series, you'd increase the overall resistance and the current would have to decrease?

Absolutely. V=IR. V isn't changing if you are hooked to a battery. If R or I changes, so does the other.

 

[OHare]

The equivalent resistor changes, yes, but the question asks about the individual resistor R2, not, not the eqivalent resistance (and current through the battery). The equivalent resistance's voltage will never change though since parallel, by definition, means same voltage. Series, on the other hand, means same current.

But when you take out or add resistors doesn the whole picture change? I thought current could adapt based on the resistors in the circuit...Like if you added another resistor in series, you'd increase the overall resistance and the current would have to decrease?

 

[antissa]

But when you take out or add resistors doesn the whole picture change? I thought current could adapt based on the resistors in the circuit...Like if you added another resistor in series, you'd increase the overall resistance and the current would have to decrease?

the current that leaves the positive terminal of the battery and arrives back at the negative terminal decreases, yes
Think of it this way: before, with two parallel resistors, you had 2x current leaving the battery. That current then split up into x and x to go to each of the two resistors. Now that one of the resistors is removed, the other resistor still has x current flowing through it, but now that's the total current in the whole circuit

 

[MDtoBe777]

Yeah. So I guess it doesn't matter if you add or remove resistors in parallel because the voltage that will end up going through each of them will always be the same. Therefore, so will the current.