# A circuit problem involving voltage/current.

1. May 29, 2012

1. The problem statement, all variables and given/known data
http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w04_qp_2.pdf
number 6b

2. Relevant equations
V=IR
E=IR+Ir maybe

3. The attempt at a solution
Im not sure why the line which is supposed to be drawn passes through the top right corner.

Also, im not sure how to go about the second part.. how to find the resistance at C? I dont know the PD across it. What am i missing?

2. May 29, 2012

### truesearch

The line you have to draw is a line with resistance 1500ohms.
When the voltage is 6 (horizontal axis) the current will be 4mA (he vertical axis)
Hope this gets you to the next step.

3. May 29, 2012

### Staff: Mentor

Pick a few values of voltage and plot the points for the resulting current through the 1500Ω resistor. Is the I/V plot for this component going to be curved or straight?
You know the total PD across both. What does that tell you about the sum of the individual PD's? In what approximate location on the graph must the circuit be operating? (hint: vary the current and estimate the PD's on both components).

4. May 29, 2012

Thanks. I missed the resistor R part :/ :/

So with the 2 graphs we estimate the current when V=2.
0.75A and 1.3 something, and add them together

5. May 29, 2012

### Staff: Mentor

Yes, that'll do it for part (b)(ii).

For some reason I was looking at part (c) when I wrote what I did about summing the potential drops. I'm glad you managed to work out the similar process for part (b)(ii)