# E field magnitude

• sasuke07

## Homework Statement

What is the magnitude of the collective contribution to the E field at the origin from both the + and - charges located 5 cm above the horizontal axis?

kQ/d^2

## The Attempt at a Solution

Im just having a problem setting up this problem. Could someone help me on getting started

#### Attachments

• charges.pdf
8.2 KB · Views: 149

hi sasuke07!

(try using the X2 button just above the Reply box )

first, find the magnitude of each contribution,

from that, find the x and y components …

what do you get?

I already figured out the magnitued of the the positive charge 5 cm above the axis and got 5.4X10^4. What do you mean by the x and y components. WOuldn't the negative charge have the same magnitude of the positive charge.

WOuldn't the negative charge have the same magnitude of the positive charge.

yes
What do you mean by the x and y components.

draw an arrow at the origin showing the direction of the field from the positive charge

then find the x and y components of that arrow

(and finally you'll add them to the x and y components of the arrow from the negative charge )

so to figure out the x component wouldn't it be Kq/d^2 where k=9X10^9, q is 30X10^9= charge and d would be .05m^2. Or would i have to use cosine and sine to figure out the x and y components and if so could you show me how to set it up.

no, you must use cos and sin, of the angle the arrow makes

so would it be Kq/r^2sintheta
and Kq/r^2Costheta. Where theta would be 90 degrees?

or would theta be 45

θ is the angle of the line from the charge to the origin

awesome so 45 degrees.

So were the equations correct though?

looks ok

so what is the total field from both the positive and the negative charge?​

i got 7.6X10^4 by doing KQ/r^2sin45 and the answer is the same for cos45. BUt i checked the answer and its supposed to be 7.1X10^4. Any suggestions

i got 7.6X10^4 by doing KQ/r^2sin45 and the answer is the same for cos45. BUt i checked the answer and its supposed to be 7.1X10^4. Any suggestions