Sandy asked in Science & MathematicsPhysics · 1 month ago

# Electric Fields?

What effect does the SIGN of the central charge have on the magnitude of the electric field and the direction of the electric field?

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• 1 month ago

It is not really clear what you are asking.

Examples might help.

• NCS
Lv 7
1 month ago

Depends on the rest of the setup.

"Central" to me suggests that you have some other charge, or charges, present. For instance, you might have a triangle or square of charges with a charge in the center. Or a ring or hollow sphere of charge with a charge in the center. ("Central" also suggests some kind of symmetry.)

So if you have some arrangement of OTHER charges, they will produce a field measured at some point in space. The central charge will also produce a field, and that field will either align with the other field (increasing its magnitude) or against the other field (reducing the magnitude). If the central charge is large enough, it could even change the direction of the field.

Example: Consider a sphere of charge totaling 10 nC and having radius R. Outside the sphere some distance d, the field is

E = k*10nC / (d + R)².

(i) Put a 20 nC charge in the middle of that sphere.

It's field (at the same point as we used before) is

E' = k*20nC / (d + R)²

and so the cumulative field has had its magnitude tripled but the direction is unchanged.

(ii) Put a -20 nC charge in the middle.

It's field (at the same point as we used before) is

E' = k*-20nC / (d + R)²

and so the direction of the cumulative field has changed but the magnitude has not.

Note that inside the sphere, the field due to the sphere's charge is zero.

And if all you have is a point charge, then @s4p is correct.

• 1 month ago

The sign has no affect on the magnitude of the electric field.

The sign controls the direction of the electric field: a positive sign gives an outwards field; a negative sign gives inwards field. See diagram:

http://web2.uwindsor.ca/courses/physics/high_schoo...