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nfoland
Feb 10, 2012, 02:09 PM
I-------I------------I
I... I... I
9V... 680ohm... 330ohms
I... I... I
I... I... 150ohms
I-------I------------I

The I's, dashes, and values represent a circuit. The periods are there to fill in the space. What is the voltage, current, and power of each resistor?

nfoland
Feb 10, 2012, 02:12 PM
It didn't make the image like I wanted it to. The 150 ohm and 330 ohm resistors are suppose to be in the same line with the 330 on top of the 150.

ebaines
Feb 10, 2012, 02:33 PM
I redrew the circuit to make it clearer. First start with the 680 ohm resistor. Since it's connected directly to the battery, the voltage across it is 9 volts. You can find current from Ohm's law (V=iR) and power from either P=V^2/R or P = i^2R.

For the resistors on the right recall that two resistors in series are like one resistor of value R1 + R2. That single equivalent resistor is connected directly to 9 volts, so the current flow from Ohm's Law is


i = \frac {9\ volts} {(R1 + R2)}
.

Now for power - there are two ways to do this:
a) since you now know the current flow through the two resistors, you can use
P_1 = i^2 R_1 and P_2 = i^2 R_2

b) or you could recognize that the voltage drops across resistor 1 and 2 are:


V_1 = 9\ volts \ \times \ \frac {R_1}{(R_1+R_)} \\
V_2 = 9 \ volts \ \times \ \frac {R_2}{(R_1+R_2)}


Then use :


P_1 = \frac {V_1^2}{ R_1} and {P_2} = \frac {V_2^2} {R_2}.

I suggest practicing both methods so you are comfortable with them.

nfoland
Feb 11, 2012, 01:17 AM
Thank you so much!