Help needed on Intro to EE, Howework Problem

[memphisBred]

Not yet, no.

So 4 resistors. Use I=p/v.

For instance... I=.025W/1V gives .025 A. Plug that into R=V/I, R=1V/.025W gives 40 ohms. So the first resistor with 1 V across it will have a resistance of 400 ohms. Then do the same for 5V, 10V, and 20 V.

Is that right?

[Wicks]

Start at the source since you have the info for that and work your way around the loop.

You have a 25V source that is outputting 25mW.

25mW/25V=......

[memphisBred]

When you get the current from the Power equation, is the next step to divide the given 1V by the found current for the first resistor's resistance?

[memphisBred]

Doing it like I think you are saying I got 1,000, 5,000, 10,000, and 20,000.

[Wicks]

When you get the current from the Power equation, is the next step to divide the given 1V by the found current for the first resistor's resistance?

Yep. You know the loop current and that the loop current x R1 = 1V.

[Wicks]

You need to split 25V into four lower voltages.

That's five different voltages in the loop, not counting the ground (0V).

How many nodes does that give you?

[memphisBred]

So when drawing the diagram, the voltage source is 25V going into the first resistor which is 1000, R2 is 5000, R3 is 10000 and R4 is 20000?

[Wicks]

Couple issues yet.

You have to keep in mind that as you move up the divider, the voltage is shared by an increasing number of resistors.

1V = R1 * i

5V = R1 * i + R2 * i

10V = R1 * i + R2 * i + R3 * i

and so on...

Also, your divider with 4 resistors has 20V at the top of the chain. That should connect to the source which is at 25V.

So you're connecting 20V and 25V which can't happen.

What are you missing?

[memphisBred]

I get the answer/how to get the resistance for 1V.

Moving onto the 5V...Do you multiply R1 times (I)^2 and divide 5V by that answer to get R2? Then that would be the actual resistance of the second resistor?

[Wicks]

I get the answer/how to get the resistance for 1V.

Moving onto the 5V...Do you multiply R1 times (I)^2 and divide 5V by that answer to get R2? Then that would be the actual resistance of the second resistor?

Write out all the formulas for all the voltages.

5V = R1 * i + R2 * i

5V = i(R1 + R2)

5V/i = R1 + R2

5V/i - R1 = R2