Register to reply 
Electric field at a distance from a charged disk 
Share this thread: 
#1
Jan2013, 02:05 AM

P: 6

A disk of radius 2.4 cm carries a uniform surface charge density of 3.1 μ C/m2. Using reasonable approximations, find the electric field on the axis at the following distances.
I have used the equation E=(Q/ε_{0})(1/(4*pi*r^{2})) I also tried the equation E=(Q/2(ε_{0}))(1(z/(√(z^{2})+(r^{2}))) Thanks in advance for the help. Both equations have not led me to the correct answer. *note, there is not a figure provided for this question* 


#2
Jan2013, 07:43 AM

Mentor
P: 41,300




#3
Jan2013, 07:58 AM

P: 1,020




#4
Jan2013, 11:37 PM

P: 6

Electric field at a distance from a charged disk
Doc Al, thanks for your quick reply. Unfortunately I am still doing something wrong. I am using 3.1E6 C/m2 for σ. Is that wrong?



#5
Jan2113, 12:05 AM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 9,644

How about you post all your working and the target answer?



#6
Jan2113, 12:14 AM

P: 6

E= (3.1E6/(2*8.85E12))(1((.0001/(√(.0001^{2})+(.024^{2}))
so E= 1.79E5 N/C where: σ=3.1E6 C/m^{2} ε_{0}=8.85E12 C^{2}/N*m^{2} z=.01E2 m r= 2.4E2 m 


#7
Jan2113, 12:34 AM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 9,644

Did you simply replace Q by σ? What about the disc area?



#8
Jan2113, 12:45 AM

P: 6

Yes, that's what I did. Is it σ=Q/A then?



#9
Jan2113, 12:58 AM

Homework
Sci Advisor
HW Helper
Thanks ∞
P: 9,644

Yes, as in the link andrien posted.



#10
Jan2113, 01:09 AM

P: 6

There was an advertisement above that link earlier so I ignored it thinking it was tied to that ad.
Alright, thanks for your help! cheers! 


#11
Jan2113, 01:13 AM

P: 6

And thank you andrien for the link!



#12
Jan2113, 01:25 AM

Mentor
P: 11,594

Note: This thread had already developed quite a bit before I noticed that it really should have been in one of the homework help forums. Therefore I've simply moved it instead of deleting it and asking the original poster to start over, which is the normal practice.
In the future, please post requests for help on specific exercises like this in one of the homework help forums, even if they're not actually assignments for a class. The "normal" forums are more for conceptual questions and general discussion of their topics. 


Register to reply 
Related Discussions  
The Electric Field of a Uniformly Charged Disk  Introductory Physics Homework  1  
Electric Field of a Charged Disk  Classical Physics  4  
The Electric Field Due to a Charged Disk  Introductory Physics Homework  1  
Electric Field Due to a Charged Disk  Introductory Physics Homework  1  
Electric Field due to a Charged Disk.  Introductory Physics Homework  2 