Point charge and electric flux

In summary, the electric flux through a sphere whose center is at a distance x and whose radius is less than x from a point charge is equal to 0. This is because the sphere does not enclose the point charge, so the enclosed charge (q_enc) is equal to 0. This results in a net flux of 0 since the electric field lines entering the sphere are equal to the ones exiting. However, the student mentions they have been given a different answer, so it is unclear what concept they may be missing.
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Homework Statement


You measure an electric field E at a distance x from a point charge. What is the electric flux through a sphere whose center is at that distance and whose radius is less than x from the charge?


Homework Equations


E*dA = (q_enc)/(e_0)


The Attempt at a Solution


I'm not sure that I'm understanding the question...The sphere does not enclose the point charge since its center is at x and its radius is less than x from the charge, so doesn't that mean q_enc = 0 and the flux is 0? (I have the answer so I know it's not zero, but I don't understand what I'm missing conceptually here...)
 
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  • #2
net flux is 0
it means the new electric field lines crossing the total surface is 0
look at pic ... all field lines entering exit the Gaussian surface ! so net field through surface is 0
 

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  • #3
channel1 said:

The Attempt at a Solution


I'm not sure that I'm understanding the question...The sphere does not enclose the point charge since its center is at x and its radius is less than x from the charge, so doesn't that mean q_enc = 0 and the flux is 0?
I believe that is correct.
(I have the answer so I know it's not zero, but I don't understand what I'm missing conceptually here...)
That's weird, what is the "correct" answer that you have been given?
 

1. What is a point charge?

A point charge is a hypothetical electrical charge that is concentrated at a single point in space and has no physical dimensions. It is often used in mathematical models to simplify the analysis of electric fields and forces.

2. How is electric flux related to point charges?

Electric flux is a measure of the electric field passing through a given area. In the case of a point charge, the electric flux is directly proportional to the strength of the electric field at a given distance from the charge.

3. What is the equation for electric flux?

The equation for electric flux is given by Φ = E*A*cos(θ), where Φ is the electric flux, E is the electric field strength, A is the area, and θ is the angle between the electric field and the normal to the surface.

4. How does the distance from a point charge affect electric flux?

The electric flux decreases as the distance from a point charge increases. This is because the electric field strength decreases with distance, resulting in a smaller amount of electric flux passing through a given area.

5. Is electric flux a vector or scalar quantity?

Electric flux is a scalar quantity, meaning it has magnitude but no direction. This is because it is a measure of the strength of the electric field passing through a given area, rather than a directional measurement.

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