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January 26, 2015

January 26, 2015

Posted by **Nilan - still need help** on Thursday, May 19, 2011 at 8:21pm.

Resistors of 30 ohms and 60 ohms are connected in parallel and joined in series to a 10 ohm resistor.

The circuit voltage is 180 volts.

Find:

a)the voltage of the parallel circuit

b)the voltage across the parallel circuit

c)the current through the 10 ohm resistor

Ans: So for voltage of parallel circuit I took 180V/30 ohms = 6A. I multiplied that by 20 ohms that I had found by 1/r total = 1/30 + 1/60 = 20 ohms. So I got 120 V for voltage of the parallel circuit.

For voltage across the parallel circuit, I originally found 180V because I included the 60 V from the series. From what the tutors have said, this is the same problem as above one. Therefore, should my answer be 120 V instead of the 180V?

c) I used I = V/R = 60 V / 10 ohsm = 6 amps for the current through the 10 ohm resistor.

So I found: 120 V, 120 V again???, and 6A. Have I finally got it?

- physics -
**bobpursley**, Thursday, May 19, 2011 at 8:33pmNuts to your logic.

voltage in the parallel branch is due to the effective resistance of the parallel branch x total current.

effective resistance of parallel branch:

20 ohms, your work is correct there.

Total resistance: that 20 ohms in series with another 10, total 30 ohms.

total current: 180/30=6amps (note this is not what you did).

voltage on parallel branch: 20ohms*6amps 120 volts

current thru 10 ohm: 6 amps.

Now your questions: what does a) mean? It makes no sense.

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