PhysicsLAB CP Workbook
Electrostatics: Induction and Conduction

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The outer electrons in metals are not tightly bound to the atomic nuclei. They are free to roam in the material. Such materials are good ____
 
Electrons in other materials are tightly bound to the atomic nuclei, and are not free to roam in the material. These materials are good ____
 
Refer to the following information for the next three questions.

A rubber rod that has been rubbed with fur is negatively charged because rubber holds electrons better than fur does. When the rod touches a metal sphere, some of the charge from the rod spreads onto the metal sphere because like charges repel one another. When the rod is removed the charge spreads evenly over the metal sphere and remains there because the insulating stand prevents its flow to the ground. The negatively charged rod has given the sphere a negative charge. This is charging by contact, and is shown to the right.


Describe how the right-hand sphere below is charged if a positively-charged rod were to touch the metal sphere.



 

In the examples above, electric charge is
 
A positively-charged balloon will stick to a wooden wall. It does this by polarizing molecules in the wooden wall to create an oppositely-charged surface. Describe how the charges are aligned on both the balloon and in the wall.

 

Refer to the following information for the next three questions.

Consider the diagrams below:
  1. A pair of insulated metal spheres, A and B, touch each other, so in effect they form a single uncharged conductor.
  2. A positively charged rod is brought near A, but not touching, and electrons in the metal sphere are attracted toward the rod. Charges in the spheres have redistributed, and the negative charge is labeled.
Discuss with your partner (b) where to draw the appropriate + signs that are repelled to sphere B. 

Then discuss where the signs of charge are in (c), when the spheres are separated while the rod is still present. 

And finally, in (d) after the rod has been removed. 

Refer to the following information for the next four questions.

Consider below a single metal insulated sphere,
 
  1. initially uncharged. When a negatively charged rod is nearby,
  2. charges in the metal are separated. Electrons are repelled to the far side. When the sphere is touched with your finger,
  3. electrons flow out to the sphere to the earth through the hand. The sphere is "grounded." Note the positive charge left
  4. while the rod is still present and your finger removed, and
  5. when the rod is removed.
 
This is an example of charge induction by grounding. In this procedure the negative rod "gives" a positive charge to the sphere.
 
The diagrams below show a similar procedure with a positive rod. Describe where the correct charges are located in each step.
 
Step b 

Step c 

Step d 

Step e 

Refer to the following information for the next question.

The distribution of electric charge in a water molecule is not perfectly even. One side is negative and the other side is positive. The molecule is electrically polarized. As a result, water molecules are attracted to each other.
Which diagram, the one on the left or the one on the right, correctly represents a pair of water molecules attracted to each other?
 
 
 
Refer to the following information for the next two questions.

One of these isolated charged spheres is copper and the other is rubber.
    
Which one is copper?
 
Which one is rubber?
 



 
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