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December 21, 2014

December 21, 2014

Posted by **Aubrey** on Saturday, March 26, 2011 at 6:15pm.

We're dealing with electrical circuits and I have to construct a circuit with resistors of 10 Ohms, 20 Ohms, 30 Ohms and 20 Ohms. The total resistance has to be 42 Ohms-Can someone direct me how to even begin to draw this-I know Parallel resistors you add sum and take the reciprocal for total and series you had them together but where do I start with this-Please help_ I'm stuck and its the weekend and this is due Monday

- Physics -
**drwls**, Saturday, March 26, 2011 at 7:27pmThe 20 and 30 ohm resistors in parallel have an equivalent resistance of 12 ohms. Put the 10 and other 20 ohm resistors in series with that.

- Physics-Please recheck -
**Aubrey**, Saturday, March 26, 2011 at 7:47pmI drew my circuit but now I'm still confused-if I have a 20 V battery, how do I calculate the current through two of the resistors(say the two parallel ones of 20 and 30

Would I use the formula

V=IR

20V =I*12Ohm(which I just figured out)

20/12 = 1.67A But now I'm stuck because I don't know how to break it down into the 20 Ohm resistor and the 30 Ohm resistor

- Physics-oops! -
**Aubrey**, Saturday, March 26, 2011 at 7:50pmIn my calculations I think I should have said V=IR

V= 20V Battery I used so

20V = I * 20 Ohm= 1A

20V = I * 30 Ohm = .67A

- Physics -
**drwls**, Saturday, March 26, 2011 at 8:00pmYour original question just asked for how to arrange the resistors to achieve a total effective resistance of 42 ohms. I told you how to do that. The total current going through each series resistor, and the battery, will be V/R = 20/42 = 0.476 Amp

The two resistors in parallel will share that current, with the lower (20 ohm) resistor getting 3/5 of it.

- Physics -
**Aubrey**, Saturday, March 26, 2011 at 8:16pmThe reason I only asked the first part was I first wanted to understand how to construct it before I figured out the rest because I have three more sets of circuits to do so now I understand that part. I wasn't trying to mislead you-I really appreciate the help alot and can now continue with the other circuits using this as a basis-Thank you again for all your assistance

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