# Homework Help: Electric Current - What Am I Doing Wrong?

1. Jan 28, 2005

### evilempire

The equation for resisitivity is R=rho*(L/A), and the equation for current is I=V/R. So for the R equation I plugged in the numbers, changing cm to .1 m, and got 30 ohms. I then divided 110 volts by 30 and got 3.7 (rounded to two sig figs), and my answer is not being taken as correct. The computer feedback system is saying 'check your units'. What have I done wrong?

Thanks.

2. Jan 28, 2005

### evilempire

One idea I had - is the proper answer done such that I=V/((rho*L)/A), which would make I equal to 367 A?

3. Jan 28, 2005

### vincentchan

the cross section area is in cm.... and the rest of your problem is in SI .....

4. Jan 28, 2005

### evilempire

Yeah, so I converted it to m, 10 cm = .1 m.

5. Jan 28, 2005

### vincentchan

and do you still got 367.... if you do... change battery for your calculator, or do the calculation by hand......

6. Jan 28, 2005

### evilempire

So it's not 367 or 3.67? Hmm...

7. Jan 28, 2005

### vincentchan

it is 3.67

8. Jan 28, 2005

### evilempire

That's what I calculated initially, but the computer program won't take it, which led me to believe there was error in my calculation. Thanks for the help, I greatly appreciate it. I'm not sure what I'm going to do about answering the problem, but it's nice to know I had it right to begin with.

9. Jan 28, 2005

### vincentchan

maybe you have to enter 3.67A.... since the computer said check your unit

10. Jan 28, 2005

### evilempire

It says 'A' outside the text box to the right, so I'm pretty sure they just want a value.

11. Jan 28, 2005

### vincentchan

10 cm^2 = .o1 m^2...did you do the convertion correctly?

12. Jan 28, 2005

### evilempire

It does? I thought 1 cm was .01 m, so 10 cm would be .1 m.

13. Jan 28, 2005

### vincentchan

but 10 cm^2 = 10 (.01 m) ^2 = 10 * .001 m^2 = .01 m^2