# Effective resistance

1. Nov 11, 2015

### Icy98

1. The problem statement, all variables and given/known data
What is the effective resistance of this circuit?

2. Relevant equations
The answer given is 3A. so it means the total effective resistance is 4 ohm. But my answer is 4.4 ohm

3. The attempt at a solution
My attempt:
1/(1/6 + 1/4)+2 = 4.4 ohm

#### Attached Files:

• ###### IMG_3970.JPG
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2. Nov 11, 2015

### andrevdh

diagram/circuit?

3. Nov 11, 2015

### Icy98

Thank you. I've just uploaded the picture.

4. Nov 11, 2015

### stockzahn

Try to draw the circuit again, but "split up" the connection in point A. What happens with R3 and the connection at its right handside?

#### Attached Files:

• ###### pf_ss1.jpg
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5. Nov 11, 2015

### Icy98

Is this correct?

6. Nov 11, 2015

### andrevdh

It is "shorted out" by the wire forming the corner, so there is in effect "no resitance" due to the wire. That means that you can redraw the circuit without the R3 resistor.

7. Nov 11, 2015

### stockzahn

You missed something. There is another cable/connection from point A to the other and of R3.

8. Nov 11, 2015

### andrevdh

Think of electric current flowing like water from the + terminal towards the - terminal of the battery.

9. Nov 11, 2015

### Icy98

What is the reason that we can omit R3?

10. Nov 11, 2015

### stockzahn

Complete the drawing from your 3rd post with the missing cable/connection. Then you will see.

11. Nov 11, 2015

### BvU

Good thread ! You really adapted quickly to the PF culture !

In the upper right of the original picture, there is a ' 0 $\Omega$ resistor ' in parallel with the 2 $\Omega$ resistor. Does that help ?

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12. Nov 11, 2015

### Icy98

Is this correct?

13. Nov 11, 2015

### stockzahn

14. Nov 11, 2015

### Icy98

Thanks a lot to stockzahn, andrevdh and BvU for helping!

15. Nov 11, 2015

### andrevdh

It's a pleasure. The potential difference over a small resistor, or in this case the corner wire, is almost zero. That means that the potential difference over the R3 resistor is also almost zero so that almost no current flows through it. It is thus not contributing to the circuit and can be ignored or eliminated.