# The Terminologys

charge 电荷

The concept of electricity arises from an observation of nature, We observe a force between objects, that, like gravity, acts at a distance. The source of this force has been given the name charge. A very noticeable thing about electric force is that it is large, far greater than the force of gravity. Unlike gravity, however, there are two types of electric charge. Opposite types of charge attract, and like types of charge repel. Gravity has only one type: it only attracts, never repels.

current 现在，潮流，电流 Current is the flow of charge.

We use the d in formula to indicate tiny zero-sized change.

Conductors and insulator 导体与绝缘体

resistor 电阻器

voltage 电压

charged particle 带电粒子

electron 电子

spontaneously 自发地

The electron move towards a lower energy state all by themselves.

we can guide electrons using wires and make them flow through electronic components —circuit design— and do interesting things along the way.

## \*

电压：表示电路中某两个节点的电势差。

电流：表示单位时间内通过导体的电荷的量。

它们的关系：有了电压，才有可能产生电流，但是有电压，未必就会产生电流。电压必须加在导体的两端，这样导体中才会产生电流，如果加在不导电的东西的两端，电压仍然存在，但是没有电流。另一方面，电流总是从电压高的地方流向电压低的地方。

Power 功率

Power is defined as the rate energy \(U\) is transformed or transferred over time.

An electric circuit is capable of transferring power. Current is the rate of flow of charge, and voltage measures the energy transferred per unit of charge.

Electrical power is the product of voltage times current. in units of watts.

### The unit of these things

ampere 安培

watt 瓦特

Volt The volt is the unit of electric potential difference—electric potential difference is also known as voltage. The size of 1 volt is officially defined as the potential difference between two points of a wire carrying a current of 1 ampere when the power dissipated in the wire is 1 watt.

ohm 欧姆

SI is the International System of Units—in French, Système International d'Unités. It is the modern form of the metric system and is the most widely used system of measurement. The system was published in 1960 as the result of discussions that started in 1948. SI is based on the metre-kilogram-second system \(MKS\). In the United States, the SI is used in science, medicine, government, technology, and engineering.

capacitor 电容器 a device used to store an electric charge, consisting of one or more pairs of conductors separated by an insulator.

2-terminal elements 二端元件

Inductor 电感器

circuit 电路

Closed circuit – A circuit is closed if the circle is complete, if all currents have a path back to where they came from.

Open circuit – A circuit is open if the circle is not complete, if there is a gap or opening in the path.

Short circuit – A short happens when a path of low resistance is connected \(usually by mistake\) to a component. For example, a wire shorts out a resistor by providing a low-resistance path for current \(probably not what the designer intended\).

Schematic A schematic is a drawing of a circuit. A schematic represents circuit elements with symbols and connections as lines.

Elements – The term elements means "components and sources."

Symbols – Elements are represented in schematics by symbols.

Lines – Connections between elements are drawn as lines, which we often think of as "wires".

Dots – Connections between lines can be indicated by dots. Dots are an unambiguous indication that lines are connected. If the connection is obvious, you don't have to use a dot.

Reference designator – When you place a component in a schematic you often give it a unique name, known as a reference designator.

Node – A junction where 2 or more elements connect is called a node.

Branch – Branches are the connections between nodes. A branch is an element \(resistor, capacitor, source, etc.\). The number of branches in a circuit is equal to the number of elements.

Loop – A loop is any closed path going through circuit elements. To draw a loop, select any node as a starting point and draw a path through elements and nodes until the path comes back to the node where you started. There is only one rule: a loop can visit \(pass through\) a node only one time. It is ok if loops overlap or contain other loops. Mesh – A mesh is a loop that has no other loops inside it.

Reference Node – During circuit analysis we usually pick one of the nodes in the circuit to be the reference node. Voltages at other nodes are measured relative to the reference node. Any node can be the reference, but two common choices that simplify circuit analysis are: 1. the negative terminal of the voltage or current source powering the circuit, or 2. the node connected to the greatest number of branches.

Ground – The reference node is often referred to as ground.

