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6 Nov 2011 12:43:53 IST

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two identical conducting spheres , fixed in space , attract each other with an electrostatic force of 0.108N when seperated by 50 cm , centre-to-centre. A thin conducting wire then connects the sphere . when wire is removed , the spheres repel each other with an electrostatic force of 0.0360N. what were the initial charges on the sphere?

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Arjun Virmani

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Joined: 1 Jun 2009

Posts: 1294

29 Jan 2012 23:31:18 IST

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The net charge present in the system remains constant...

and force between two bodies due to charges = k q Q / r²

for case 2

since the spheres were connected the charges on both the spheres will be the same.

0.036 = k q *q / r²

k = 9 * 10⁹ Nm²c^-2 (for air)

r = 50 cm = 0.5 m

^{so u'll get q from here.}

BEFORE WIRING:

as they were attracting they had opp. charges.

thrfr, this charge will be on 1st sphere. + the charge that cancelled out on wiring.

let the charge on 2nd sphere be Q (-ve) (before wiring)

charge on 1st = q+ Q (opp. to 2nd thrfr, +ve)

force = k q (q+Q) / r²

form here u can get Q.

and thrfr charges before wiring.

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