physics help please ?????

Question

pt1 
Two identical conducting spheres are placedwith their centers 0.21 m apart. One is givena charge of +1.2 × 10−8 C and the other acharge of −1.6 × 10−8 C.Find the magnitude of the electric forceexerted by one sphere on the other.The value of the Coulomb constant is8.98755 × 109 N · m2/C2.Answer in units of Npt 2   The spheres are connected by a conductingwire.After equilibrium has occurred, find theelectric force between them.Answer in units of N.

nyphdinmd · Answer

Gauss's law lets you treat the two spheres as point charges so the electric field for each sphere is:

E_i = k*q_i/r^2  where i =1 for sphere 1 and i = 2 for sphere 2 and r = 0.21 m

Since force on a charge is the charge time the electric field acting on it then:

F_i,j = q_i * E_j  where 1 not equal j and i,j = 1 or 2  so

F_1,2 = F_2,1 = kq_1*q_2/r^2 = -3.9129 x 10^-5 N

Now connect the spheres with a wire.  The net charge is (-1.6 + 1.2)x10^-8C = -0.4 x 10^-8C

This net charge, call it Q will divide equally between the two spheres so the new force is

F_new = k*(Q/2)(Q/2)/(r^2) = 8.152x10^-7 N

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physics help please ?????

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