How do I find the equivalent resistance between terminals A and F? The only idea I had was simplifying the parallel 300 and 60 resistors, but where to from there?


| improve this question | | | | |
  • \$\begingroup\$ That's a good start. You might find a series combination to simplify next. If necessary, redraw each simplified circuit and post where you get stuck. \$\endgroup\$ – Brian Drummond Jan 16 '16 at 16:39
  • \$\begingroup\$ That's a start. Parallel the 300/60,series with the 50,parallel with the 150, and ignore the 200. \$\endgroup\$ – WhatRoughBeast Jan 16 '16 at 16:39
  • \$\begingroup\$ Does that mean there is no current flowing throught the 200? \$\endgroup\$ – Quant Jan 16 '16 at 16:42

You can redraw it like this:


simulate this circuit – Schematic created using CircuitLab

| improve this answer | | | | |

1, below, is the original problem.

In 2, the 300 and 60 ohm resistors in parallel resolve to an equivalent resistance of:

$$ Rt = \frac {300 \Omega \times 60\Omega}{360\Omega+60\Omega} = 50 \text{ ohms,}$$ morphed to RA lower down.

RA is in series with R4, for a total of 100 ohms, and that 100 ohms is in parallel with R3, as shown in 3 with the resistors rearranged for clarity.

The equivalent resistance of R3, R4, and RA, then, will be:

$$ Rt = \frac {(RA +R4) \times R3}{RA+R4+R3} = 60 \text{ ohms} $$

The total resistance from A to F, then, is the sum of the 60 ohms connected to A, the 200 ohms connected to F, and the 60 ohms in series between them.

enter image description here

| improve this answer | | | | |
  • \$\begingroup\$ Thank you for the detailed answer! One thing that's confusing me with these problems is the order I'm solving the resistors. For example, I would've solved (2) this way: 50 and 50 in series give 100, which is parallel to the 150. This gives us 60 ohms. Finally, the equivalent resistance would be 60 + 60 + 200 = 320 ohms. I don't know if I'm wrong in my judgment, but my first reaction was this. How can these solutions not match? Thanks \$\endgroup\$ – Quant Jan 16 '16 at 18:32
  • \$\begingroup\$ @Quant you are correct, it is 320 Ohm. \$\endgroup\$ – Steve G Jan 16 '16 at 19:34
  • \$\begingroup\$ I apologize for the sloppy work. It is, indeed, 320 ohms. \$\endgroup\$ – EM Fields Jan 16 '16 at 20:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.