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 by anonymous
    

1 Answer

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

http://answermenu.com/1148/three-negative-point-charges-lie-along-line-shown-the-figure
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!



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