Question

Five Styrofoam balls are suspended from insulating threads. Several experiments are performed on the balls; and the following observations are made: Ball A attracts B and A repels C. Ball D attracts B and D has no effect on E. A negatively charged rod attracts both A and E. What are the charges, if any, on each ball? A B C D E

Answer 1

Force between balls will be attractive if both balls have opposite charge and Force between ball will be repulsive if both balls have same signs.

Now Given that

Ball A attracts Ball B, So A and B will have opposite signs

Ball A repels Ball C, So A and C will have same signs

Ball D attracts Ball B, So D and B will have opposite signs

Ball D has no effect on E, which means Both D and E will have zero charge on them. (Since ball B attracts ball D is also given, it will be possible because positive or negative charge of B will induce some opposite charge on ball D)

Negative charged rod attracts A, which means charge on A is +ve

Now Since A is +ve, and A attracts B, So It means B is -ve

Now Since A is +ve, and A repels C, So It means C is +ve

So correct Sequence is A = +ve, B = -ve, C = +ve, D = 0, E = 0

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