A circuit problem involving voltage/current.

[thoradicus]

Homework Statement

http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_w04_qp_2.pdf
number 6b

Homework Equations

V=IR
E=IR+Ir maybe

The Attempt at a Solution

Im not sure why the line which is supposed to be drawn passes through the top right corner.

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

 

[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.

 

[gneill]

Homework Statement

http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Physics%20%289702%29/9702_w04_qp_2.pdf
number 6b

Homework Equations

V=IR
E=IR+Ir maybe

The Attempt at a Solution

Im not sure why the line which is supposed to be drawn passes through the top right corner.

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?

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

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).

 

[thoradicus]

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

 

[gneill]

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

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)