Find E_r & E_θ for Grounded Conducting Sphere in Uniform Electric Field

In summary, the problem involves a grounded conducting sphere in a uniform electric field with potential V(r,θ) = -Vo(1 - (R/r)3)*cosθ. The task is to find Er and Eθ using the equations -∂V/∂r and -1/r ∂V/∂θ. The equations should be valid for this problem as they are derived from the definition of electric field in spherical-polar coordinates. The question also asks for the surface charge distribution of the sphere, which can be interpreted as the surface charge density σ = q/A.
  • #1
nmsurobert
288
36

Homework Statement


Grounded conducting sphere in uniform electric field has potential
V(r,θ) = -Vo(1 - (R/r)3)*cosθ

Find Er and Eθ.

Homework Equations

The Attempt at a Solution


In the textbook I found
Er = -∂V/∂r

Eθ = -1/r ∂V/∂θ

Those are in the chapter we're working with but those two equations are in the section talking about the electric field of dipoles. Do those equations apply for the problem I'm working on?
 
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  • #2
By definition: ##\vec E = -\vec\nabla V## ... you will need ##\nabla## in spherical-polar coordinates.

Check how the equations in your book were derived - make sure you understand the reasoning involved. Then you can make a determination about how appropriate they are for your situation.
 
  • #3
Simon Bridge said:
By definition: ##\vec E = -\vec\nabla V## ... you will need ##\nabla## in spherical-polar coordinates.

Check how the equations in your book were derived - make sure you understand the reasoning involved. Then you can make a determination about how appropriate they are for your situation.
the front of the book has a legend for the gradient in spherical coordinates so i used that. the question was just worded weird.

also, the question asks for "surface charge distribution of the sphere".
is that just the surface charge density?

σ = q/A?
 
  • #4
or ρ = ∈o∇E
 
  • #5
nmsurobert said:
the front of the book has a legend for the gradient in spherical coordinates so i used that. the question was just worded weird.
Then you have the answer to your first question - well done.

also, the question asks for "surface charge distribution of the sphere".
is that just the surface charge density?
This is another odd wording I think. You seem quite good at figuring this stuff out...
How would you normally express a charge distribution?
 
  • #6
The word "distribution" is what's throwing me off but if this were an exam I'd say it's asking for area charge density. That's how the charge is distributed over the surface per unit area.
 

Related to Find E_r & E_θ for Grounded Conducting Sphere in Uniform Electric Field

What is the formula for calculating E_r and E_θ for a grounded conducting sphere in a uniform electric field?

The formula for calculating E_r (radial electric field) and E_θ (tangential electric field) for a grounded conducting sphere in a uniform electric field is:

E_r = -E_θ = -E₀cos(θ)

Where E₀ is the strength of the electric field and θ is the angle between the direction of the electric field and a point on the surface of the sphere.

How does the electric field affect the charges on a grounded conducting sphere?

In a grounded conducting sphere, the electric field will cause the charges to redistribute themselves on the surface of the sphere. The charges will accumulate on the side of the sphere closest to the source of the electric field, resulting in a non-uniform charge distribution.

What is the significance of the grounded condition in this scenario?

The grounded condition means that the conducting sphere is connected to a conducting path that leads to the ground. This allows the sphere to maintain a constant potential and ensures that the electric field inside the sphere is zero. Without this condition, the electric field inside the sphere would be non-zero and the charges would not distribute themselves in the same way.

Can the formula for calculating E_r and E_θ be used for any type of conducting sphere?

Yes, the formula can be used for any type of conducting sphere as long as it is in a uniform electric field and is grounded. The only difference between different types of conducting spheres may be the shape or size, which would affect the angle θ at different points on the surface.

How does the angle θ affect the distribution of charges on the surface of the sphere?

The angle θ affects the distribution of charges as it determines the direction and magnitude of the electric field at different points on the surface of the sphere. At θ = 0 (directly facing the electric field), the charges will be evenly distributed, but as θ increases, the charges will accumulate on one side of the sphere.

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