Electric Fields and charged particles

[TheExibo]

Let's say there's a question where there are two charges placed, and a point in between and above the line connecting the two charges forms a triangle like this:

http://session.masteringphysics.com/problemAsset/1413940/2/p19.5.jpg

What would one have to do in order to find the electric field at point P? Would it be having to use the component method to find the x and y values, then using Pythagorean theorem and so on?

(I couldn't use the template for this post)

 

[Bystander]

find the x and y values, then using Pythagorean theorem and so on?

Don't doubt yourself when you do understand something. You're in business.

 

[TheExibo]

Don't doubt yourself when you do understand something. You're in business.

I tried using that to find the y values, added them up, yet its too large. The net x value in the actual question is 0 in the center of the two charges.

 

[Bystander]

The net x value in the actual question is 0 in the center of the two charges.

Check.

yet its too large.

Let's see your numbers for the y component.

 

[TheExibo]

Check.

Let's see your numbers for the y component.

The height of the triangle is the square root of 3m. An electric field at this distance away from one of the points would have a magnitude of 17980N/C. Multiplying that by two because there are two charges gives a magnitude of 35960N/C upward. The correct answer is 1.2x10^5N/C.

 

[Bystander]

The height of the triangle is the square root of 3m

It's an attractive short cut, and like all shortcuts, it's the farthest distance between two points. You have to sum each charge increment times the inverse square of its distance from the point. If the distance is much greater than the distance between charges, what you've done is a reasonable approximation, but not the case here.
Take one more swing at it, please.

 

[TheExibo]

You have to sum each charge increment times the inverse square of its distance from the point

I'm not sure what you mean here. Is the distance in the y-axis? The hypotenuse? Also, I check and the answer in the book isn't correct. So the answer that I got is not correct?

 

[Bystander]

The hypotenuse?

Yes.
You want the absolute distance between each charge and the point at which you're calculating the field.

the book isn't correct

I was going to get to that.

answer that I got is not correct?

More correct than the book, but you need to use the hypotenuse.
One more time.

 

[haruspex]

You have to sum each charge increment times the inverse square of its distance from the point.

Remembering that these are vectors to be summed.

The correct answer is 1.2x10^5N/C

That's way too much.

 

[TheExibo]

The electric field intensity at a point 2m away from one of the charges is 13485N/C which is the hypotenuse. I know the angle at the bottom two vertices are 60 degrees. Doing (13485N/C)sin60 gives an answer of 11678N/C. Multiplying that by two gives 23357N/C upward. Is this the correct process?

 

[Bystander]

You nailed it, round to the appropriate number of significant figures, and have a happy.

 

[TheExibo]

You nailed it, round to the appropriate number of significant figures, and have a happy.

Thanks! :D