# Help with linear charge density and flux

• artsakh

## Homework Statement

The y-axis carries a uniform linear charge density of -2 nC/m, and there is a 8 nC point charge
at the point (3 cm, 0 cm, 0 cm) as well as a -4 nC point charge at the point (-8 cm, 0 cm, 0 cm).
What is the electric flux through a closed spherical surface of radius 4 cm centered at the origin?

## Homework Equations

I know that flux is 4πkQin or Qin0, i don't understand where the linear charge density comes in. I know that the 8nC charge would be inside the sphere.

## The Attempt at a Solution

I tried adding the linear charge density and the 8nC charge and putting it through that formula but i don't understand how the -4nC charge affects the flux, or how to factor it in.

Any help would be greatly appreciated

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The charge outside the sphere doesn't affect the flux, correct? when adding the charges inside the sphere, -2 and 8, which gives 6nC, and putting it through the formula, 4πkQin, i get 678.58, but the correct answer is 886Nm2/C

You are correct that the charge outside the sphere has no influence.
You have made a mistake in determining the charges inside. While there is one charge of 8nC, the 2nC/m is a charge density, not a charge itself.
You need to calculate the amount of charge within the sphere given this charge density, and the radius of the sphere. How might that be accomplished?

well i have the equation E = 2kλ/r. E = k8nC/(.08)2?? but how does that help??

Just think about the charge on the y-axis for a moment.
It has a charge density -2nC/m. The sphere is radius 0.04m, so what is the total charge (on the y-axis) inside the sphere?