Chapter 21, Problem 91A

a.

To determine

Whether the charges of two oil drops suspended in Millikan experiment the same.

Explanation of Solution

Introduction:

Charged bodies when placed in an electric field experience force. In the experiment, the weight of the oil drop is balanced by the force by the electric field.

The charges of the two oil drops can be different because the two oil drops can be of different masses and hence to balance them in the electric field, they need to hold different charges.

Conclusion:

The charges can be different for different oil drops of different masses.

b.

To determine

The ratio of the two properties which have to be equal so that the drops stay motionless.

Explanation of Solution

Introduction:

Charged bodies when placed in an electric field experience force. In the experiment, the weight of the oil drop is balanced by the force by the electric field.

The charges of the two oil drops can be different because the two oil drops can be of different masses and hence to balance them in the electric field, they need to hold different charges. Therefore, the ratios of the charge to mass must be equal to hold the oil drops in balance.

Conclusion:

The ratios of the charge to mass must be equal to hold the oil drops in balance.