## Mastering Physics Solutions: The Electric Field Inside a Conductor

Charging an Insulator

Part A = The nuclei experience a force to the right and the electrons experience a force to the left.
Part B = The electrons move to the left and the nuclei are almost stationary.
Part C = left end negative and right end positive
Part D = It will point to the left and oppose the initial applied field.

Solutions Below:

Learning Goal: To understand how the charges within a conductor respond to an externally applied electric field.

To illustrate the behavior of charge inside conductors, consider a long conducting rod that is suspended by insulating strings (see the figure). Assume that the rod is initially electrically neutral, and that it remains so for this discussion. The rod is positioned along the x axis, and an external electric field that points in the positive x direction (to the right) can be applied to the rod and the surrounding region. The atoms in the rod are composed of positive nuclei (indicated by plus signs) and negative electrons (indicated by minus signs). Before application of the electric field, these atoms were distributed evenly throughout the rod.

Part A

What is the force felt by the electrons and the nuclei in the rod when the external field described in the problem introduction is applied? (Ignore internal fields in the rod for the moment.)

• Both electrons and nuclei experience a force to the right.
• The nuclei experience a force to the right and the electrons experience a force to the left.
• The electrons experience a force to the left but the nuclei experience no force.
• The electrons experience no force but the nuclei experience a force to the right.

The nuclei experience a force to the right and the electrons experience a force to the left.

Part B

What is the motion of the negative electrons and positive atomic nuclei caused by the external field?

• Both electrons and nuclei move to the right.
• The nuclei move to the right and the electrons move to the left through equal distances.
• The electrons move to the left and the nuclei are almost stationary.
• The electrons are almost stationary and the nuclei move to the right.

The electrons move to the left and the nuclei are almost stationary.

Part C

Imagine that the rightward current flows in the rod for a short time. As a result, what will the net charge on the right and left ends of the rod become?

• left end negative and right end positive
• left end negative and right end negative
• left end negative and right end nearly neutral
• left end nearly neutral and right end positive
• both ends nearly neutral

left end negative and right end positive

Part D

The charge imbalance that results from this movement of charge will generate an additional electric field near the rod. In what direction will this field point?

• It will point to the right and enhance the initial applied field.
• It will point to the left and oppose the initial applied field.

It will point to the left and oppose the initial applied field.

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