Question

Four lightweight balls $A,B,C,andD$are suspended by threads. Ball $A$has been touched by a plastic rod that was rubbed with wool. When the balls are brought close together, without touching, the following observations are made:

• Balls $B,C,andD$are attracted to ball $A.$

• Balls $BandD$have no effect on each other.

• Ball $B$is attracted to ball $C.$

What are the charge states (glass, plastic, or neutral) of balls $A,B,C,andD$? Explain.

Short answer

charge state of glass rubbed with ball A becomes positive, ball B becomes neutral, plastic rubbed with ball C becomes negative, ball D becomes neutral.

Step-by-step solution

Given information

Four lightweight balls $A,B,CandD$are suspended by threads.

Ball $A$has been touched by a plastic rod that was rubbed with wool.

When the balls are brought close together, without touching.

Explanation

The following observations made are:

• Balls $B,CandD$are attracted to ball $A$: When ball $A$is touched near to plastic, it becomes negative and the other balls $B,CandD$are positive and are attracted to ball $A$.

• Balls $BandD$have no effect on each other: When balls $AandC$are charged and when $BandD$are neutral charged, so that balls $BandD$have no effect on each other.

• Ball $B$is attracted to ball $C$: When ball B is neutrally charged, it will be attracted to ball $C$since it was positively charged.

On the whole, charge state of glass rubbed with ball A becomes positive, ball B becomes neutral, plastic rubbed with ball C becomes negative, ball D becomes neutral.