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A physics student believes that she has found an experimental way to apply some mysterious "third" type of charge to a plastic sphere that is hung by a string.

The student observes that the sphere is gently attracted to both a positively-charged rod and a negatively-charged rod. The student concludes that the sphere is charged neither positive nor negative, but charged in some other "third" way that attracts both positive and negative charges.

Which arguments below could be correctly used to convince the student that they arrived at a faulty conclusion?

Select TWO answers.


The plastic sphere is likely neutral after touching the student’s fingers. However the charges in the sphere can polarize and the sphere can show slight attraction to both of the rods.


The plastic sphere must be negative. The student was acting as a ground and the ground gives excess electrons into the plastic sphere.


The student should repeat the same experiment several times and expect to see different results.


Any electric charge results from a deficiency or an excess of negatively-charged electrons. Thus, macroscopic objects can only have two kinds of charge, positive or negative.

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