# Three negative point charges lie along a line as shown in the figure.

+1 vote

Three negative point charges lie along a line as shown in the figure. Find the magnitude and direction of the electric field this combination of charges produces at point P, which lies 6.00 cm from the -2.00 microC charge measured perpendicular to the line connecting the three charges.

I've used the Pythagorean theorem to find the d for the outside two electric fields, E1 and E2. And I know the y components cancel out because the charges are negative and counteract. I've also converted the cm to m and the microCoulombs to Coulombs.

Here's what I have:
E1 = (8.99x10^9)(-2x10^-5)/(.06m)^2 = 4994.44 N/C

E2 = (8.99x10^9)(-5x10^-6)/(.1m)^2 = 4495000 N/C x cos 53.1 = 4.495 x 10^6
E3 = (8.99x10^9)(-5x10^-6)/(.1m)^2 = 4495000 N/C x cos 53.1 = 4.495 x 10^6

Adding up the Y vectors, I got 5.40 x 10^6; but this answer is wrong. I've been told that it needs to be some number x 10^7, but I have no idea what I'm doing wrong. Could someone please show me with steps what I'm doing wrong? It would really be helpful!

asked Jan 25, 2013 in Physics

+1 vote
Hi, I was looking at this question and i think its the same as what youre asking!

answered Jan 25, 2013 by anonymous
I went back through my stuff with a proverbial fine-toothed comb and found the error. I had my E1 charge as 2 x 10^-9 instead of 2 x 10^-6. When I re-added everything up, it came out to 1.398 x 10^7. Somehow this answer is still wrong. Any help?
Figured it out finally. Had another miscalculation in how I entered something into my calculator. The link you posted was helpful the 2nd time through. Thank you for your help!
congrats! glad you finally solved it!