# Point charge and electric flux

• channel1
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.

## 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...)

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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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.