# Physics Olympiad question Electric circuit

Tags:
1. Nov 11, 2015

### Hashiramasenju

1. The problem statement, all variables and given/known data

In the Circuit(pic attached) the following resistor combination is found.
All the resistrs in the figure has resistance R ohms.
What is the total resistance across AB?
2. Relevant equations

V=IR
3. The attempt at a Solution
between point A and B there is only one resistor so i thought the answer is R

#### Attached Files:

• ###### IMG_20151111_201517.jpg
File size:
28 KB
Views:
233
2. Nov 11, 2015

### Staff: Mentor

No, there are multiple paths that current could take from A to B. Look for opportunities to combine series and parallel resistances to reduce the circuit complexity.

Your Relevant Equations should have included the formulas for combining resistances.

3. Nov 11, 2015

### Hashiramasenju

I could do the part i) im stuck with the part ii)

4. Nov 11, 2015

### Staff: Mentor

Show your work for part (i) and what you've tried for part (ii).

5. Nov 11, 2015

### Hashiramasenju

This is for part i)
But for part ii) i seriously had no idea.

6. Nov 11, 2015

### Staff: Mentor

Part i) work is good.

For part ii), can you not spot any series or parallel connections? What type of connection relationship do resistors AD and DC have?

7. Nov 11, 2015

### Hashiramasenju

yeah i noticed that resistors ad and dc are in series. Then resistors ac is parallel with ad&dc. so the only resistor left out is bc

8. Nov 11, 2015

### Staff: Mentor

Yes, so can you reduce the whole network down to a single resistance?

9. Nov 11, 2015

### Hashiramasenju

no. I really have no idea how to include resistance ab and bc in the circuit

10. Nov 11, 2015

### Staff: Mentor

You've already identified that AD is in series with DC and so can be replaced by a single resistor, say "ADC". You also pointed out that this ADC is in parallel with AC, so that pair in turn can be replaced with a single resistor. What's the value of that resistor?

Redraw the circuit with that new resistor in place and the remaining resistors.

11. Nov 11, 2015

### Hashiramasenju

I think i got it 5R/8
Thank you !!!!!!!!!!!!!!!!!!!!!

12. Nov 11, 2015

### Staff: Mentor

Looks good.

You're welcome