# Physics II - B1

## Electric Charge (Điện tích)
1. **Positive or Negative**
2. **Conserved**
* Charge is not created in the process of rubbing two objects together.
* The electrification is due to a transfer of charge from one object to another.
4. **q = N.e**
> **N is an integer**
> **|e| = 1.6 x 10^-19^ $(C)$**

## Electrical Condutors (Chất dẫn điện)
* **Electrical conductors** are materials in which some of the electrons are free electrons.
* Free electrons are not bound to the atoms
* Electrons can move freely through the material.
* Good conductor: copper, aluminum and silver.
* When a good conductor is charged in a small region, the charge readily distributes itself over the entire surface of the material

## Electrical Insulators (Chất cách điện)
* **Electrical insulators** are materials in which all of electrons are bound to atoms.
* Electrons can not move freely through the material.
* Good insulators: glass, rubber and wood.
* When a good insulator is charged in a small region, the charge is unable to move to other regions of the material.

## Semiconductors (Chất bán dẫn)
* The electrical properties of **semiconductors** are somewhere between those of insulators and conductors.
* Semiconductor materials: silicon and germanium.
* Used in making electronic chips.
* The electrical properties of semiconductors can be changed by the addition of controlled amounts of certain atoms to the material.

## Electrostatics
**Electrostatics**: Tĩnh điện
## Charging by induction
* Charging by **induction** (hiện tượng cảm ứng điện từ) requires no contact with the object inducing the charge.
* Examples: See more on powerpoint.

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## Coulomb's laws
* The force is a **conservative force** (chỉ phụ thuộc vào điểm đầu và điểm cuối, không phụ thuộc vào đường đi).
* The force is inversely proportional to the square of the separation.(**Inverse - square law**)


* Like charges repel = repel
* Unlike charges attract = attract

## Superposition principle (Nguyên lý chồng chất)
* The **resultant force** on any one charge equals the **vector sum** of the forces exerted by the other individual charges that are present.

## Electric dipole (Lưỡng cực điện)

<img src = https://i.imgur.com/TeKN42d.png width = 600 height = 400>

## Assignments

<img src = https://i.imgur.com/FiT0QWu.png width = 600 height = 500>

$$
S^2 = 2F^2 - 2.cos2\alpha.F^2
$$

$$
S^2 = 2F^2.(1-cos2\alpha) = 4.F^2.sin^2\alpha
$$

$$
S = 2.F.sin\alpha
$$

$$
S = \frac{k.q^2.d}{(r^2 + \frac{d^2}{4})^\frac{3}{2}}
$$

## Other references
* [MIT Physics 2](https://www.youtube.com/playlist?list=PLyQSN7X0ro2314mKyUiOILaOC2hk6Pc3j)
* [Michel van Biezen](https://www.youtube.com/playlist?list=PLX2gX-ftPVXX7BZOcM1Y2gb8IQrTBrmUB)
* [Khan Academy](https://www.khanacademy.org/science/in-in-class-12th-physics-india)

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