Where is the Electric Field Equal to Zero?

[mrlucky0]

Yeah. Posted too hastily...Fixed

 

[learningphysics]

Cool. So you want the field created by the 3rd charge to cancel this one... so it has the same magnitude and opposite direction... I recommend first calculating r using:

kq/r^2 = 1.2E7

 

[mrlucky0]

The field created by the third charge is then

-Enet = < 3E6, -1.2E7 >

(9E9)(85E-6)/r^2 = 1.2E7 ==> r = .25

Looks good?

 

[learningphysics]

The field created by the third charge is then

-Enet = < 3E6, -1.2E7 >

(9E9)(85E-6)/r^2 = 1.2E7 ==> r = .25

Looks good?

Yeah... looks good. I'm a little worried about the number of decimal places we're keeping... I think more would be better, but no big deal...

Do you have an idea about where the third charge should be (the angle)? you can get the angle from the field...

 

[mrlucky0]

Yeah... looks good. I'm a little worried about the number of decimal places we're keeping... I think more would be better, but no big deal...

Do you have an idea about where the third charge should be (the angle)? you can get the angle from the field...

Regarding decimal places, I will go through the problem again with more accuracy no worries at this point.

How about getting the angle using inverse tangent:

I know < 3E6, -1.2E7 >.

tan(a) = (1.27E7/ 3E6) ==> a = 76 degrees

 

[learningphysics]

Regarding decimal places, I will go through the problem again with more accuracy no worries at this point.

How about getting the angle using inverse tangent:

I know < 3E6, -1.2E7 >.

tan(a) = (1.27E7/ 3E6) ==> a = 76 degrees

Yeah, so now you should be able to get x and y from 76 and r=0.25

 

[mrlucky0]

I forgot. 76 degrees is relative to the -x axis so 104 degrees is relative to the +x axis:

.25 < cos(104), sin(104) >
= <-6E-2, 2.4E-1>

The signs of the coordinate make sense to me. Success?

 

[learningphysics]

I forgot. 76 degrees is relative to the -x axis so 104 degrees is relative to the +x axis:

.25 < cos(104), sin(104) >
= <-6E-2, 2.4E-1>

Cool! Yeah, I tend to just use the acute angles, and the sketch to keep track of the signs (positive or negative x, y etc...)... But how you did it is exactly right.

 

[learningphysics]

I forgot. 76 degrees is relative to the -x axis so 104 degrees is relative to the +x axis:

.25 < cos(104), sin(104) >
= <-6E-2, 2.4E-1>

The signs of the coordinate make sense to me. Success?

Yup.

 

[mrlucky0]

Wow. Thank you so much. I just joined this forum today and I'm so glad I did. This was a positive experience. You are of great help.

 

[learningphysics]

Wow. Thank you so much. I just joined this forum today and I'm so glad I did. This was a positive experience. You are of great help.

You're welcome! Yeah, it's a great forum.