Electric field at a distance from a charged disk

In summary, the conversation focused on finding the electric field on the axis at certain distances from a disk with a radius of 2.4 cm and a uniform surface charge density of 3.1 μ C/m2. Two equations were mentioned, with one being identified as the correct one to use and the other needing to be adjusted to replace Q with σ. The conversation also included clarifying questions and a link to a source with more information.
  • #1
kb1408
6
0
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/ε0)(1/(4*pi*r2))
I also tried the equation E=(Q/2(ε0))(1-(z/(√(z2)+(r2)))

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*
 
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  • #2
kb1408 said:
I have used the equation E=(Q/ε0)(1/(4*pi*r2))
This looks like the field from an infinite sheet of charge. You should write it as σ/2ε, where σ is the surface charge density. Not what you want.
I also tried the equation E=(Q/2(ε0))(1-(z/(√(z2)+(r2)))
That's the one you want, but you need to replace Q with σ.
 
  • #4
Doc Al, thanks for your quick reply. Unfortunately I am still doing something wrong. I am using 3.1E-6 C/m2 for σ. Is that wrong?
 
  • #5
How about you post all your working and the target answer?
 
  • #6
E= (3.1E-6/(2*8.85E-12))(1-((.0001/(√(.00012)+(.0242))
so E= 1.79E5 N/C
where:
σ=3.1E-6 C/m2
ε0=8.85E-12 C2/N*m2
z=.01E-2 m
r= 2.4E-2 m
 
  • #7
Did you simply replace Q by σ? What about the disc area?
 
  • #8
Yes, that's what I did. Is it σ=Q/A then?
 
  • #9
Yes, as in the link andrien posted.
 
  • #10
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
And thank you andrien for the link!
 
  • #12
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.
 

1. What is an electric field?

An electric field is a physical quantity that describes the influence of an electric charge on other charges within its vicinity. It is represented by vectors that indicate the direction and strength of the force that a charged particle would experience if placed in that field.

2. How is the electric field at a distance from a charged disk calculated?

The electric field at a distance from a charged disk can be calculated using the formula E = σ/2ε₀, where E is the electric field, σ is the surface charge density of the disk, and ε₀ is the permittivity of free space.

3. What factors affect the strength of the electric field at a distance from a charged disk?

The strength of the electric field at a distance from a charged disk is affected by the surface charge density of the disk, the distance from the disk, and the permittivity of the medium surrounding the disk.

4. How does the direction of the electric field at a distance from a charged disk change?

The direction of the electric field at a distance from a charged disk changes based on the orientation of the disk. If the disk is positively charged, the electric field lines will point away from the disk, and if it is negatively charged, the field lines will point towards the disk.

5. What is the role of electric field at a distance from a charged disk in everyday life?

The electric field at a distance from a charged disk plays a crucial role in many everyday technologies, such as touchscreens, capacitors, and charged particle accelerators. It is also responsible for the attraction and repulsion between charged objects, as well as the flow of electricity in circuits.

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