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PrashntS
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Homework Statement
Two point charges 2q and 8q are placed at a distance r apart. Where should a third charge -q be placed between them so that the electrical potential energy of the system is minimum.
a). at a distance r/3 from 2q
b). at a distance 2r/3 from 2q
c). at a distance r/16 from 2q
d). none of these
Homework Equations
PE of system= PE between all the individual charges.
EPE of two point charges can be given as: 1/4πε * q1*q2 / r
The Attempt at a Solution
I simply derived the equation of potential energy of system, which is:
http://i46.tinypic.com/nvt72s.jpg
Then I differentiated the equation to find out the value of x where potential energy is minimum.
I got x = 2r + 8 +- sqrt( 5r^2-8r+16)
Now the problem is I dnt know whether my solution is correct. Since the question is MCQ, i ticked none of these. which, hopefully was correct. Need help.
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