Skip to Content Skip to Header Navigation
Getting your Trinity Audio player ready...

Hold down the T key for 3 seconds to activate the audio accessibility mode, at which point you can click the K key to pause and resume audio. Useful for the Check Your Understanding and See Answers.

Name That Charge - help4

There are some fundamental principles that one will have to understand and use in order to successfully analyze all seven Name That Charge situations. Those fundamental principles are ...

  1. Electrons are negatively charged and protons are positively charged.
  2. Only electrons are able to move during electrostatic charging processes.
  3. Opposites attract and likes repel. Thus, electrons are attracted to positively-charged objects and repelled by negatively-charged objects and by each other.
  4. If a neutral object gains electrons, then it becomes negatively charged. If a neutral object loses electrons, then it becomes positively charged.

There are a few nearly-identical versions of this question. Two of the versions include:

Version 1:

A negatively-charged foam board is on the table. A neutral aluminum pie tin is held above it. The pie tin is then touched. Once touched, what is the charge on the pie tin? What is the charge on the foam board?

Polarization Step

Charging Step
A charged object is brought near to a neutral object.
 

The neutral object is touched to the ground.

Version 2:

A positively-charged acrylic plate is on the table. A neutral aluminum pie tin is held above it. The pie tin is then touched. Once touched, what is the charge on the pie tin? What is the charge on the acrylic plate?

Polarization Step

Charging Step
A charged object is brought near to a neutral object.
 

This question is an example of charging by induction. Charging by induction typically involves a two-step process - a polarization step and a charging step. In the polarization step, a neutral object is brought near to a charged object . This induces a movement of electrons within the neutral object. Think about fundamental principle #3 (above) to determine how electrons move. In the charging step, the neutral object is touched to a third object (sometimes referred to as the ground). There is a transfer of electrons between the third object and the neutral object. Once more, fundamental principle #3 will help you determine the direction in which electrons move.

In this process, there is NEVER any transfer of electrons between the charged object and the neutral object that is being charged. Thus the charged object will keep the same amount and type of charge that it originally had.

Charging by Induction