NCERT Class XII Chapter
Electric Charges and Fields
Questions With Solutions

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Question : 13
Total: 34
Suppose the spheres A and B in previous question have identical sizes.
A third sphere of the same size but uncharged is brought in contact with the first, then brought in contact with the second, and finally removed from both. What is the new force of repulsion between A and B?
Solution:  

The new force of repulsion between A and B is
F'' =
1
4πε0
q1"×q2"
(r")2

or F" = 9 × 109 ×
3.25×107×4.875×107
(0.5)2
or F" = 5.7 × 103 N
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