# What is the electric field at x=2d?

## Homework Statement

Positive point charges q and 2q are located at x=0 and x=3d respectively. What is the electric field at x=2d?

E=kQ/r^2

## The Attempt at a Solution

E1=kq/(2d)^2=kq/4d^2
E2=2kq/d^2
E1-E2=7kq/4d^2, to the left

To the left is correct but the answer is wrong :( can someone please tell me why? thanks.

It should be the negative of that. Small mistake but you did everything else correctly.
-7kq/4d^2

It should be the negative of that. Small mistake but you did everything else correctly.
-7kq/4d^2

When I said left, that was intended to mean the sign was negative. In my online homework, for vectors we can not put in actual signs. For example we have to put it in this format:

magnitude of vector, direction.

that is why i said 7kq/4d^2, to the left--assuming to the right is positive and to the left is negative.

but it's still saying that is wrong :(

You're work is right; either the format is wrong, or the program has the wrong solution.

Are you sure you're not supposed to plug in for k or something?

SammyS
Staff Emeritus