Q.

Following observations are made after performing several experiments on five styrofoam balls which are suspended from insulating threads.
(i) Ball attracts and repels
(ii) Ball has no effect on and attracts
(iii) Both and are attracted by a negatively charged rod
If an electrically neutral styrofoam ball is placed nearby a charged body, it gets attracted due to induced charge. Find the charges, if any, on each ball.

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Solution:

and has no effect on each other that means they are neutral.
A repels and attracts , That means and has similar charges and has opposite charge to that of .
A negatively charged rod attracts , That means is positively charged, hence is negatively charged and is positively charged.