Can a neutral insulator be attracted to a charged object?

[jumbogala]

Homework Statement

Hi all. I'm a teacher and one of my students asked me a question I couldn't answer today. It's a multiple choice question:

A neutral object is attracted to an electrically charged rod. The two are not touching. The neutral object:

A. is a conductor
B. is an insulator
C. could be either a conductor or an insulator

The answer key said A is correct.

Homework Equations

The Attempt at a Solution

Reasoning of the answer key:

• The neutral object is attracted to the rod because of an induced charge separation within the object.
  
• Induced charge separations involve electrons shifting within the object.
  
• In an insulator, electrons are fixed in place and cannot shift, so this object must be a conductor. Thus the answer is A.

However, earlier in the course, I showed the students that a charged rod can attract neutral pieces of paper. Paper is an insulator... so what gives? Is it just a bad test question?

Here is my guess: Perhaps within insulators you can still have some electron shifting, enough to attract them to charged things. However maybe the attraction would be weak. For a conductor there would be a lot more electron shifting and a stronger attraction. So should the answer to the test question actually be B?

 

[TSny]

It's a good question, but answer A is the wrong answer. As you noted (and demonstrated), insulators are attracted to charged objects. The shifting of charge in an insulator corresponds to polarization of molecules.
http://www.physicsclassroom.com/class/estatics/Lesson-1/Polarization

So should the answer to the test question actually be B?

What about C?

 

[jumbogala]

It's a good question, but answer A is the wrong answer. As you noted (and demonstrated), insulators are attracted to charged objects. The shifting of charge in an insulator corresponds to polarization of molecules.
http://www.physicsclassroom.com/class/estatics/Lesson-1/Polarization

What about C?

Thanks for the link - it explains perfectly. So in a conductor, the shifting of charges corresponds to the "electron sea" in metals being more concentrated on one end of the object compared to the other. However, in an insulator, the electrons still stay with their molecules, but each molecule is polarized, which can lead to an attraction.

Oops - yes, the answer should be C! I wasn't being careful when I chose B.