Potential Difference of Capacitors


by AdKo
Tags: capacitors, difference, potential
AdKo
AdKo is offline
#1
Feb18-07, 01:50 AM
P: 19
1. The problem statement, all variables and given/known data
A parallel-plate capacitor has an area of 5 cm^2, and the plates are separated by 1mm with air between them. The capacitor stores a charge of 400pC. a) What is the potential difference across the plates of the capacitor? b) What is the magnitude of the uniform electric field in the region between the plates?


2. Relevant equations
1. [tex]U_{c}=\frac{1}{2}C(\Delta V)^2[/tex]
2. [tex]C=\epsilon_{0}\frac{A}{d}[/tex]

3. The attempt at a solution
a) Using equation #1, [tex]\Delta V=\sqrt{\frac{2(400*10^-12C)}{(4.425*10^-10F)}}[/tex]

V=1.3446 V ... however, the answer in the back of the book is: 90.4 V
What am I doing wrong here? I'm pretty sure I'm using the right equation.

b) E=V/d I plugged in the book's answer for V and used the given distance to find the electric field magnitude. Help me on part a please? Thanks!
Phys.Org News Partner Science news on Phys.org
SensaBubble: It's a bubble, but not as we know it (w/ video)
The hemihelix: Scientists discover a new shape using rubber bands (w/ video)
Microbes provide insights into evolution of human language
hage567
hage567 is offline
#2
Feb18-07, 09:55 AM
HW Helper
P: 1,542
Your first equation listed doesn't make sense for this problem. That is the equation for the energy stored in a capacitor, which you don't know (U does not equal the charge). Try to find a simplier equation containing the three things you know.
For your calculation of C using equation 2: You answer isn't quite right. I suspect you didn't convert the area from cm^2 to m^2 properly.
AdKo
AdKo is offline
#3
Feb18-07, 11:45 AM
P: 19
Quote Quote by hage567 View Post
Your first equation listed doesn't make sense for this problem. That is the equation for the energy stored in a capacitor, which you don't know (U does not equal the charge). Try to find a simplier equation containing the three things you know.
For your calculation of C using equation 2: You answer isn't quite right. I suspect you didn't convert the area from cm^2 to m^2 properly.
thanks for all your help. I solved by using C=Q/V that was easy.


Register to reply

Related Discussions
Potential difference across capacitors, can someone check this? Introductory Physics Homework 1
Potential Difference and Potential Near a Charged Sheet Introductory Physics Homework 1
Electric potential, potential difference, and potential energy Introductory Physics Homework 2
Difference in capacitors Electrical Engineering 5
Capacitors and Potential Difference Introductory Physics Homework 1