Understanding the Attractive Force of a Positive Charge Near a Neutral Conductor

[dzza]

I am just reviewing some E&M because i took the class before I ever thought i had that big of an interest in physics and just memorized formulas, etc. Anyway, this is from a "which of the following statements is true" question.

The true statement is: A positive charge experiences an attractive electrostatic force near a neutral conductor.

The alternatives were that it experiences a repulsive force, no force, ...

How come the true statement is indeed true as opposed to a positive charge experiencing no electrostatic force near a neutral conductor?

 

[Teecher]

Charge redistributes itself on the surface of the conductor in response to the presence of the charge. Negative charges are brought close to the positive charge, resulting in a net attraction.

 

[berkeman]

The true statement is: A positive charge experiences an attractive electrostatic force near a neutral conductor.

Is that true? I wouldn't have expected that "true statement". That would mean that an isolated charge (like an electron) is attracted to neutral atoms... I didn't know that was true...

 

[Teecher]

There must be a redistribution of charge if the surface of the conductor is to remain an equipotential. This induced polarization results in a potential that goes as 1/r⁴ (the usual dipole goes as 1/r², plus an extra 1/r² to account for the decreasing strength of the induced dipole with distance). This does have an analog in atomic/molecular interactions, often referred to as charge-induced dipole forces.