Difference between Induction and Polarization

Regarding the Induction and Polarization, this article will explain the information below.

• Difference between Induction and Polarization
• [Electrostatic induction and dielectric polarization] Electric field and Electric Potential

Induction vs Polarization

Electrostatic induction is a phenomenon that occurs when a charged body is brought close to a conductor, causing a bias in the charge inside the conductor.

Inside a conductor (a material that conducts electricity, such as a metal) are free electrons. Free electrons are electrons that can move freely inside the conductor and have a negative charge. Therefore, when a charged body is brought close to a conductor, the free electrons inside the conductor are subjected to electrostatic force and move.

As a result, the inside of the conductor near the charged body generates a charge different from that of the charged body, while the conductor far from the charged body generates the same charge as the charged body. This phenomenon of biased charge inside a conductor caused by bringing a charged body close to the conductor is called electrostatic induction.

For example, in the above figure, a positively charged body is approached from the left side of the conductor. In this case, the left side of the conductor (the side closer to the charged body) is negatively charged and the right side of the conductor (the side farther from the charged body) is positively charged.

Dielectric polarization is a phenomenon that occurs when a charged body is brought close to an insulator, causing a bias in the charge inside the insulator.

When a charged body is placed close to an insulator (a material that does not conduct electricity, such as an underlay), the electrons (which have a negative charge) in the molecules and atoms inside the insulator are subjected to electrostatic forces. The electrons inside the insulator are not free electrons that can move freely. Therefore, the electrons cannot leave the molecule or atom, resulting in a charge bias in individual molecules and atoms. In other words, the entire insulator is subject to charge bias.

As a result, the inside of the insulator produces a charge different from that of the charged body on the "side close to the charged body" and the same charge as the charged body on the "side far from the charged body. This phenomenon of biased electric charge inside an insulator caused by bringing a charged body close to the insulator is called dielectric polarization.

For example, in the above figure, a positively charged body is approached from the left side of the insulator. In this case, the left side of the insulator (the side closer to the charged body) is negatively charged and the right side of the insulator (the side farther from the charged body) is positively charged.

[Electrostatic induction and dielectric polarization] Electric field and Electric Potential

In electrostatic induction and dielectric polarization, this section describes graphs of electric fields and electric potentials.

The above figure shows the graphs of electric field and electric potential when the following objects are inserted between the "polar plates storing positive charge" and the "polar plates storing negative charge".

• In case nothing is inserted
• In case an insulator (with small dielectric constant) is inserted
• In case an insulator (with a large dielectric constant) is inserted
• In case a conductor is inserted

In case nothing is inserted

An electric field is generated from a positive charge to a negative charge. Since the strength of the electric field is constant, the electric potential varies linearly.

In case an insulator (with small dielectric constant) is inserted

When an insulator (with a small dielectric constant) is inserted between the pole plates, dielectric polarization occurs inside the insulator.

Due to dielectric polarization, a part of the electric field from outside and the electric field inside the insulator cancel each other out, and the electric field inside the insulator is weakened.

Since the insulator cancels out part of the electric field from outside, the lines of electric force pass through the inside of the insulator.

In other words, since an electric field exists inside the insulator, a electric potential difference is generated inside the insulator.

In case an insulator (with a large dielectric constant) is inserted

When the dielectric constant of an insulator is large, the polarization of the insulator increases and the electric field from the outside is cancelled out to a greater extent.

Therefore, compared to an insulator (with a small dielectric constant), the electric field inside the insulator becomes smaller, and the number of lines of electric force passing through the insulator decreases.

As a result, the electric potential difference generated inside the insulator also becomes smaller.

In other words, the larger the dielectric constant of the insulator, the smaller the electric potential difference inside the insulator.

In case a conductor is inserted

When a conductor is inserted between the pole plates, electrostatic induction occurs inside the conductor.

In the above figure, the left side of the conductor is negatively charged because free electrons are moving to the left side of the conductor. On the other hand, the right side of the conductor is positively charged because the number of free electrons is reduced.

There is no electric field inside the conductor because the free electrons move until they cancel out the electric field from the outside. In other words, there is no electric potential difference inside the conductor.

Summary

This article described the following information about "Induction and Polarization".

1. Difference between Induction and Polarization
2. [Electrostatic induction and dielectric polarization] Electric field and Electric Potential

Thank you for reading.