# What would a voltmeter read if it were connected between the surface of the cylinder

1. Feb 10, 2010

### kimm

.A very long insulating cylindrical shell of radius 6.00 cm carries charge of linear density 8.90*10^-6 C/m spread uniformly over its outer surface.
*What would a voltmeter read if it were connected between the surface of the cylinder and a point 4.70 above the surface. and What would a voltmeter read if it were connected between the surface and a point 1.00 from the central axis of the cylinder?

I started with this equation
delta V= ( lemda/ 2pi epslion) (ln(rb/ra))

2. Feb 10, 2010

### uart

Re: What would a voltmeter read if it were connected between the surface of the cylin

distance units? 4.7 ???, 1.0 ???

Ok so presumably you've substituted your numbers into this formula and got an answer. What exactly is the problem?

Last edited: Feb 10, 2010
3. Feb 10, 2010

### uart

Re: What would a voltmeter read if it were connected between the surface of the cylin

BTW. Assuming the above are both in units of cm, then your equation is valid for the first measurement but not for the second one. Do you know why?

Last edited: Feb 10, 2010
4. Feb 10, 2010

### kimm

Re: What would a voltmeter read if it were connected between the surface of the cylin

i did like this
(8.90* 10^-6/ 2 pi 8.85*10^-12)ln (4.5/6)
i got -39084.73
what i am not sure about is ln ra and ln rb
i substituted ra cm and rb 4.5 cm

5. Feb 10, 2010

### kimm

Re: What would a voltmeter read if it were connected between the surface of the cylin

ra is 6 cm

6. Feb 10, 2010

### uart

Re: What would a voltmeter read if it were connected between the surface of the cylin

Well for one I don't even get that answer when I use your numbers. Double check your calculator usage.

In any case the numbers you're using are not correct. I think you should be using Ra = 6cm and Rb = 10.7 cm.

Are the distances of 4.7 and 1.0 methioned in you question in cm ????????

7. Feb 10, 2010

### uart

Re: What would a voltmeter read if it were connected between the surface of the cylin

Oh thanks for clarifing that. It was the ONLY distance in your original question that you did include units for. So what a great idea to repeat that one instead of clarifying the units of the other distances that you didn't include units for. I'm going to give up here.

8. Feb 10, 2010

### kimm

Re: What would a voltmeter read if it were connected between the surface of the cylin