Finding the magnitude and direction of the electric field

[cvc121]

Homework Statement

13. Find the magnitude and direction of the electric field at P due to the two charges shown.

Homework Equations

The Attempt at a Solution

I have attached both the question, which involves a diagram, as well as my attempt at the answer below. My first question is regarding direction. Since the charge on point P is not known, how do you know the directions of the other two charges in order to draw the vector diagram if you don't know whether they attract or repel P? Also, the answer given is 1.87 x 10^10 N/C [E 15.5 S] but I get the answer to the power of 22. All help is very much appreciated! Thanks!

 

[cnh1995]

There is no charge at point P. It is just a point under influence of the electric fields of the two charges.

 

[cvc121]

Oh, okay. But then how do you determine the directions in order to draw the vector diagram? Is a positive charge always towards the East and a negative charge South, in this case? Also, is my answer to the power of 22 correct because I am certain that you need to convert microcoulombs to coulombs and mm to m.

 

[cnh1995]

Is a positive charge always towards the East and a negative charge South, in this case?

In this case, yes. Field lines of +ve charge are away from the charge and field lines of -ve charge are towards the charge.

Also, is my answer to the power of 22 correct because I am certain that you need to convert microcoulombs to coulombs and mm to m.

I haven't calculated the answer. But if converting the units gives you 10²², then you should go with that answer.

 

[gneill]

cvc121: What's the power of ten exponent for the micro (μ) prefix? Don't confuse micro with mega !