# Calculate Resistance and resistivity

1. Feb 18, 2016

### Steelers72

I have voltage, diameter, area, and inverse area data values. How could I calculate the resistance and resistivity with these numbers? I am pretty sure resistance is R=V/I and resistivity= RA/L , so I am not sure how I can calculate resistance without an I value.

2. Feb 18, 2016

### sophiecentaur

You are right. If you aren't told either R or both V and I, you cannot find resistivity. Are you trying to answer a Question in a book? Perhaps the current value is hidden somewhere else.

3. Feb 18, 2016

### Steelers72

Im not sure. It was a lab. Very frustrating because current is mentioned anywhere

4. Feb 18, 2016

### alw34

5. Feb 18, 2016

### sophiecentaur

Yes: frustrating if you can't go back and do it again. It can be difficult if you are working to a set of instructions which are presented in steps but without the necessary background. I don't know where you can go from here to get an actual result - but you have sussed out the theory now so everything isn't lost.

6. Feb 18, 2016

### alw34

Tip for labs:
Before any lab, always know what your outputs, that is results, should be. Know what you are looking for.

Then you determine before the lab what measurements, what variables, are required during the lab.

7. Feb 18, 2016

### Steelers72

Thanks for the advice. I wish there was a manual it is all written in paragraph form. Annoying.

8. Feb 18, 2016

### sophiecentaur

Absolutely. Just following your nose through a series of measurements can often lead you nowhere. Despite the 'learning by doing' mantra that's practiced in many places, getting to know the theory first is much more reliable.

9. Feb 18, 2016

### sophiecentaur

The theory isn't in manuals - it's in text books, which have probably been better thought out than a set of lab instructions.

10. Feb 18, 2016

### alw34

good point. If you had lab partners and they recorded what you need get it. Otherwise go back to the lab instructor explain your problem and do it over. I taught EE labs as a grad student and several times people came back to do some additional work...no big deal.