the material is over coulombs law, and i am having a rough time understanding the business of the sign's of the charges and the direction of the charge at the same time. here is a problem from the text.:(adsbygoogle = window.adsbygoogle || []).push({});

Two charges are located on the x axis with q1 = 2.3 x 10^-8 C at the orgin, and with q2 = -5.6 x 10^-8 C at x = 1.30 meters. Find the force exerted by these 2 charges on a third charge of q3 = 3.3 x 10^-8 C which is located at x=.24 m on the x axis.

ok so i set off to calculate the force exerted by each charge on q3, and then add them together to get the net charge.

for Q1 and Q3 the calculation is ===>

((9.0 x 10^9)(2.3 x 10^-8)(3.3 x 10^-8))/.24^2 = 1.18 x 10^-4 N

i dont understand what direction this charge is? since it is positive does it go to the right? but to the right of q1 or q3? it is a positive charge but can it have negative direction?

ok, so for the second part (q3 and q2) i have,,,,

((9.0 x 10^9)(3.3 x 10^-8)(-5.6 x 10^-8))/(1.3-.24)^2 = -1.48 x 10^-5 N

well, in the answer for this problem the calculation is set up exactly the same way, only they use a POSITIVE 5.6 x 10^-8 in their calculation for the charge of q2, even though in the problem it states that this charge is negative. i don't understand. since the charge for q3 is positive, these 2 charges are attracting each other. would this tend to increase the magnitude of the resultant force of one charge on the other?

im used to negative and positive indicateing direction on vectors, but here it seems to say that you will have negative charges in the negative direction, and likewise for positive?

can you please help clear this up at all? specifically with regards to the problem i stated and why they changed the sign of q2 in their calcualtion of the answer.

thanks

-chris

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# Homework Help: Sign and direction on charges, coulumbs law

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