Answers to p70 Exercises


1.                  For each of the questions below,  choose one of the following possible charges for the object mentioned:

·        Neutral

·        Positive

·        Negative


a.                   After rubbing her feet on the carpet, Graziella’s body acquired the same charge as that of chloride__negative______

b.                  A piece of plastic was repelled by a positive piece of plastic___ positive ___

c.                   When rubber is rubbed with silk, rubber gains electrons from silk. That leaves silk with this charge__(+)____

d.                  This object has less protons than electrons____ negative ______

e.                   This object has the same charge as helium______neutral___

f.                    Object A repels a positive charge. Object B attracts A. Object C repels B. C=_____ negative ____

g.                   If little pieces of an object are attracted to a negatively charged comb, then the object can be either ___neutral___ or ___(+)_______.


2.                  If you comb your hair repeatedly on a dry day, that comb will attract small neutral pieces of paper. Use a drawing to show why this happens.




3.                  When any two of the substances from the following list are rubbed together, the one that is higher on the list becomes negatively charged.


·        Rubber

·        Silk

·        Wool

·        Glass


If you rub a rubber ball with a woolen sweater, how will the ball behave towards a glass ball that has been rubbed with a silk shirt?


Rubber (-)

Wool (+)




Rubber(-) will attract the glass ball(+).


4.         a.          Show what will happen to the electroscope if it is approached but not touched by a negatively charged object.

b.                  Repeat for a positively charged object.