Question

Q.56> Two copper spheres A and B of same size have charges q and q respectively. They exert a force F on each other. A third
copper sphere C of same size, charge 2q is brought in contact with sphere A and then in contact with sphere B. Finally it is removed
from both. Find the new force between A and B if they are placed at the same distance as earlier.
​

Answer 1

Answer:

Q

A

=6.5×10

−7

Q

B

=6.5×10

−7

Let the uncharged sphere be C.

Q

C

=0

After contacting with A, the charge gets divided equally between A and C.

So, the new charges on A and C are 6.5×10

−7

/2 and 6.5×10

−7

/2, respectively.

Now when we brought into contact C and B, the total charge on B and C again gets divided equally between B and C.

So, the new charges on B and C are

2

3.25×10

−7

+6.5×10

−7

and

2

3.25×10

−7

+6.5×10

−7

, respectively.

So now,

Q

A

′

=3.25×10

−7

Q

B

′

=4.875×10

−7

Electrostatic force now is F=Q

A

′

Q

B

′

/4πϵ

o

r

2

=5.7×10

−8

N