Possible Duplicate: Why does the light bulb\'s brightness decrease? So I have a
ID: 1375546 • Letter: P
Question
Possible Duplicate:
Why does the light bulb's brightness decrease?
So I have a circuit in the picture with three resistors.
If I were to remove/disconnect R2 from the circuit, what would happen to the overall brightness of R3 and R1?
Now the answer I already have is that R1's brightness will go down and R3 will go up.
I understand that R1's brightness goes down because by removing the R2, the net resistance goes up (destroying a parallel combination)
But I don't understand why R3 would go up? Conceptually this makes no sense to me. How do I know that the new current would always be larger than when the current splits at the junction?
I would like a conceptual physics answer and not equations comparing inequalities.
Explanation / Answer
The following answer is, I hope, at least plausible-sounding. It is by no means a proof, and ultimately you do need the equations to make a convincing argument, because not all plausible sounding arguments end up being correct when put to the test.
The fundamental idea is that R2 is limited in its ability to set the total current in the circuit because the current will always have to travel through R1.
The answer is easiest to understand when R2 is tiny compared to R3. Then R2 acts to leech away current from R3 because it provides a path of lesser resistance. Even though a small value of R2 will cause more current to flow through the entire circuit than if R2 were larger, the current can never get too large because it always has to travel through R1 first. On the other hand, the ability for R2 to leech current away from R3 is not really limited by anything. So it should seem reasonable that removing R2 in this case would increase the current flowing through R3.
The same argument basically applies for larger values of R2, but the amount by which the current in R3 increases when you remove R2 will get smaller and smaller if you consider larger and larger values of R2. In the end, you're always restoring more current to R3 that had been trickling through R2 than the amount of current you remove from the circuit by removing R2. This comes back to the idea that R2 is limited in its ability to set the total current in the circuit.