Electric Field due to Two Point Charges

[cse63146]

Homework Statement

Two point charges are placed on the x axis. The first charge, q1= 8 nC, is placed a distance 16m from the origin along the positive x axis; the second charge, q2= 6 nC , is placed a distance 9m from the origin along the negative x axis.

Find the electric field at the origin, point O.

Give the x and y components of the electric field as an ordered pair. Express your answer in Newtons per coulomb to three significant figures. Keep in mind that an x component that points to the right is positive and a y component that points upward is positive.

Now, assume that charge q2 is negative; q2 = -6 nC. What is the net electric field at the origin, point O?

Give the x and y components of the electric field as an ordered pair. Express your answer in Newtons per coulomb to three significant figures. Keep in mind that an x component that points to the right is positive and a y component that points upward is positive.

Homework Equations

E = \frac{kQ}{r^2}

The Attempt at a Solution

I start by "placing" a test charge at the origin.

Here's what I think I should do:

E = \frac{kQ_1}{r^2} + \frac{kQ_2}{r^2}

E_1 = \frac{(9x10^9)(8x10^-9)}{16^2} = 0.261 N/C

E_2 = \frac{(9x10^9)(6x10^-9)}{9^2} = 0.667 N/C

E = E_1 + E_2 = 0.261 + 0.667 = 0.928 N/C

Am I right?

 

[Midy1420]

The direction of the E-field is taken to be the direction of the force it would exert on a positive test charge so when you draw a diagram with a positive test charge how would the forces from the q1 and q2 be acting on it? In the same direction or opposite?

 

[cse63146]

The direction of the E-field is taken to be the direction of the force it would exert on a positive test charge so when you draw a diagram with a positive test charge how would the forces from the q1 and q2 be acting on it? In the same direction or opposite?

Since all of the charges are positive, they would repel, and thus create a force pushing it to the left.

Still not sure (electircity isn't my strong point)

 

[Midy1420]

q1 is to the right of the test charge (placed at the origin) and q2 is to the left of it.. draw a force diagram to see

 

[cse63146]

ohhhh... I thought the second charge was also placed on the positive x-axis

so would it be 0.667 - 0.261 since the force is pushing the test charge to the left?

and I just noticed that I posted it in the wrong section. Would someone be able to move it to intro physics?