Chapter 20, Problem 1CQ

Four lightweight balls A, B, C, and D 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, and D are attracted to ball A.
• Balls B and D have no effect on each other.
• Ball B is attracted to ball C.

What are the charge states (positive, negative, or neutral) of balls A, B, C, and D? Explain.

To determine

To explain: The charge states of balls A, B, C and D.

Answer to Problem 1CQ

The charge states of balls A, B, C and D are negative, neutral, positive, and neutral respectively.

Explanation of Solution

The plastic rod acquires a negative charge, when it is rubbed by wool. Initially, when the rod touches the ball A, it gets polarized and acquires a negative charge. Hence, the charge on ball A is negative.

Balls B, C, and D are attached to ball A:

Balls B, C, and D are attached to ball A due to the attraction force because unlike charges attract. This is possible only if charges on balls B, C, and D are either positive or neutral.

Balls B and D have no effect on each other:

This statement indicates that the balls B and D neither attracted nor repulsed with each other. The like charges repel and unlike charges attract. Therefore, balls B and C posses no charge either positive or negative. Hence, balls B and D are neutral.

Ball B is attracted to ball C:

This statements concludes that the ball C is charged and that is the reason the neutral ball B is attracted towards C. From first statement, it is obvious that the charge of ball C must be either positive or neutral. Ball C is not neutral and hence the charge on ball C is positive.

Conclusion:

Thus, the charge states of balls A, B, C and D are negative, neutral, positive, and neutral respectively.