How would I calculate the voltage drop across the 60 ohm resistor without knowing the voltage? also, would the total circuit resistance be 7.74 ohms?
closed as unclear what you're asking by Andy aka, Rev1.0, JIm Dearden, uint128_t, Daniel Grillo May 2 '16 at 12:23
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I'm going to suggest the same thing I suggest every time questions involving lots of resistors arise. Circuits are topological, meaning that as long as you don't change which nodes are connected, you can draw the circuit however you like.
These questions are specifically formatted to be in a topology which is difficult to follow if you haven't yet built up the confidence to do so. Don't be afraid to redraw them into something more friendly. I tend to suggest you make everything vertical with sources increasing the distance of any node from the bottom of the diagram (they are adding voltage), and resistors decreasing the distance (they drop voltage). Furthermore, you can then unjumble the resistors to try and se which are in series and which are in parallel.
Here is the same diagram as the question redrawn. Hopefully now you can see where you went wrong on part (a).
We don't give direct answers to homework questions here — we expect you to show your work so far and explain exactly how you're stuck. But I'll give some hints:
How would I calculate the voltage drop across the 60 ohm resistor without knowing the voltage?
You don't need to know the voltage. The drop across the 60Ω resistor is going to be the same as the drop across the network to its right.
also, would the total circuit resistance be 7.74 ohms?
No. Isn't it obvious that it must be greater than 80Ω, because of the two series-connected 40Ω resistors?
Simple..!! If 30 ohm resistor conducts 1 amp of current, the 15 ohm in parallel with it must able to conduct 2Amps with 30V across it. Then the 5 ohm must have 3A and 15V across it.
Thus across 60 ohm, voltage must be 45.
Total R is not difficult... Think of it.