Question 1

Why is the electric field zero inside a conductor at electrostatic equilibrium?

Accepted Answer

At electrostatic equilibrium, free electrons in the conductor migrate until they create an induced electric field that exactly opposes the external field. The net field inside becomes zero because the external and internal fields cancel completely. From Gauss's law, a zero electric field means no net charge is enclosed within the conductor's volume.

Question 2

What happens to free electrons when a conductor is placed in an external electric field?

Accepted Answer

Free electrons migrate opposite to the external electric field direction, accumulating at one surface of the conductor. This creates a region with excess electrons and a region with fewer electrons, causing the conductor to polarize. The electron movement continues until the induced electric field balances the external field, establishing electrostatic equilibrium.

Question 3

How does conductor polarization relate to surface charge distribution?

Accepted Answer

When a conductor polarizes, electrons accumulate at one end, creating a negatively charged region, while the opposite end becomes positively charged due to electron depletion. These opposite charges at the surface generate an induced electric field inside the conductor. The surface charge distribution is responsible for creating the internal field that eventually cancels the external field.

Question 4

What does Gauss's law tell us about charge inside a conductor?

Accepted Answer

Gauss's law states that the electric flux through a closed surface equals the enclosed charge divided by permittivity. Since the electric field inside a conductor is zero at equilibrium, the flux is zero, meaning no net charge exists inside the conductor. All excess charge resides on the conductor's surface.

Question 5

How long does it take for a conductor to reach electrostatic equilibrium?

Accepted Answer

A conductor reaches electrostatic equilibrium very quickly when placed in an external electric field. Free electrons rapidly redistribute across the conductor until the induced electric field matches the external field magnitude. This rapid charge redistribution establishes the equilibrium state where the net field vanishes and electron motion ceases.

Question 6

What is the relationship between the external field and the induced field inside a conductor?

Accepted Answer

The induced electric field inside a conductor develops opposite to the external field direction as electrons accumulate at the surface. At electrostatic equilibrium, the induced field magnitude equals the external field magnitude, causing their vector sum to be zero. This balance prevents further charge movement and maintains the zero net field condition.

Question 7

Does conductor polarization persist after an external charge is removed?

Accepted Answer

No, conductor polarization is temporary and depends on the presence of external charges. When the external charge is removed, the separated electrons migrate back and neutralize the positive region. The conductor returns to its neutral state, and the induced electric field disappears.

導体の内部の電界

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