Electric Polarization

Claimed Edit by Eleanor Thomas Fall 2016

The Main Idea

Electric polarization is the process of inducing an object to separate charges inside it. One portion of the object would be mostly positive charges and the other portion would be mostly negative.

When an object is charged, either positively or negatively, it is attracted to another object through polarization. Even if the net charge of the second object is zero, it would still be attracted to the first object. Although the neutral object initially does not make an electric field that attracts or repels the charged object, the charged object affects the neutral object to be an induced dipole. However, this dipole is not permanent. If the charged object is removed, there would be no electric field applied and no polarization. The induced dipole will go back to being a neutral object.

Cause of Polarization

Structure of atom explains polarization. Protons in an atom are in the nucleus, and they are tightly bound. However, electrons located in the electron cloud of an atom are loosely bound compared to the protons. Therefore, the electrons can be induced to move to one side of the atom, and this phenomenon causes polarization of the atom, making it to be an induced dipole.

Conductors and Insulators

Polarization for insulators occurs in a different manner from conductors. When a conductor is polarized, electrons move across the surface of one side of the conductor to the other side. Unlike conductors, in insulators, electrons are not able to freely move around. Thus, individual molecules in the insulators are polarized, but electrons move only small distance compared to the case in conductors, so the charges are not on the surface of the object. Excess charges on conductors can only exist on the surface, while they exist anywhere on or inside insulators.

Misconception

Polarization is a different idea from charging or discharging. While polarization causes a separation of charges in an object, it does not cause imbalance of charges, which forms a charged object. Polarization still maintains an equal number of protons and electrons in an object. Therefore charging is a different discussion from polarization.

Mathematical Model

Induced Polarization : [math]\displaystyle{ \vec{P} = \alpha \vec{E} }[/math] "P" is the dipole moment of polarized atoms, "α" is the polarizability of a particular material, and "E" is the applied electric field. This equation shows that the amount of induced polarization is directly proportional to the magnitude of the applied electric field.

Examples

Simple

Question: An electric field is applied to a neutral object by a charged particle near it. After the neutral object is polarized, the particle is removed. What is the charge of the object?

Answer: The object is neutral once again. Polarization is induced by the charged particle; therefore, it is not permanent.

Middling

Question: A balloon is rubbed against a person's hair. The balloon is then placed next to a wall. You observe that the balloon sticks to the wall. How is the cause of this phenomenon?

Answer: The balloon attained electrons from the person's hair, and when put near the wall, it polarizes the wall so that electrons in the wall move farther away. Then electrons in the balloon are attracted to positively charged surface of the wall.

Difficult

Question: Draw polarization of a plastic block when a negatively charged balloon is placed near it.

Answer: Since a plastic block is an insulator, electrons in the block move small distance from their original location unlike conductors, in which electrons move freely and move to a surface when polarized.

Connectedness

Polarization is one of the main ideas in electricity and occurs whenever there is a charged object near another object. Real life applications includes when a balloon sticks to a wall after it is charged. Balloon causes the wall to polarized, and it is attracted to it in the air.

Polarization is connected to my major, mechanical engineering, since using charged object as a material for designing something would require the person to take consideration possible interaction or attraction of the invention with other objects due to polarization.

Polarization is a process that is used for certain charging methods. For example, induction charging is when polarization causes a neutral object to be a induced dipole, and the positive part of it attracts electrons, making the object to be negatively charged.

History

Benjamin Franklin was the first person to use "positive" and "negative" in describing charges and came up with principle of conservation of charges. In 1897, J.J. Thomson experimented with cathode rays and found out that electrons exist in the rays. In 1911, Ernest Rutherford discovered that atoms have a concentrated positive center with protons fixed inside nucleus.

https://www.aip.org/history/gap/Franklin/Franklin.html

Matter and Interactions Fourth Edition by Ruth W. Chabay, Bruce A. Sherwood

Electric Polarization

Contents

The Main Idea

Cause of Polarization

Conductors and Insulators

Misconception

Mathematical Model

Examples

Simple

Middling

Difficult

Connectedness

History

See Also

Further Reading

Application

External Links

Reference

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