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# 电子代写|电路基础代写Circuit Fundamentals代考|ELECENG221 Systems of Units

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## 电子代写|电路基础代写Circuit Fundamentals代考|Systems of Units

As electrical engineers, we must deal with measurable quantities. Our measurements, however, must be communicated in a standard language that virtually all professionals can understand, irrespective of the country in which the measurement is conducted. Such an international measurement language is the International System of Units (SI), adopted by the General Conference on Weights and Measures in 1960. In this system, there are seven base units from which the units of all other physical quantities can be derived. Table $1.1$ shows six base units and one derived unit (the coulomb) that are related to this text. SI units are commonly used in electrical engineering.
One great advantage of the SI unit is that it uses prefixes based on the power of 10 to relate larger and smaller units to the basic unit. Table $1.2$ shows the SI prefixes and their symbols. For example, the following are expressions of the same distance in meters $(\mathrm{m})$ :
$$600,000,000 \mathrm{~mm} \quad 600,000 \mathrm{~m} \quad 600 \mathrm{~km}$$

## 电子代写|电路基础代写Circuit Fundamentals代考|Charge and Current

The concept of electric charge is the underlying principle for explaining all electrical phenomena. Also, the most basic quantity in an electric circuit is the electric charge. We all experience the effect of electric charge when we try to remove our wool sweater and have it stick to our body or walk across a carpet and receive a shock.

Charge is an electrical property of the atomic particles of which matter consists, measured in coulombs (C).
We know from elementary physics that all matter is made of fundamental building blocks known as atoms and that each atom consists of electrons, protons, and neutrons. We also know that the charge $e$ on an electron is negative and equal in magnitude to $1.602 \times 10^{-19} \mathrm{C}$, while a proton carries a positive charge of the same magnitude as the electron. The presence of equal numbers of protons and electrons leaves an atom neutrally charged.
The following points should be noted about electric charge:

1. The coulomb is a large unit for charges. In $1 \mathrm{C}$ of charge, there are $1 /\left(1.602 \times 10^{-19}\right)=6.24 \times 10^{18}$ electrons. Thus realistic or laboratory values of charges are on the order of $\mathrm{pC}, \mathrm{nC}$, or $\mu \mathrm{C}$.
2. According to experimental observations, the only charges that occur in nature are integral multiples of the electronic charge $e=-1.602 \times 10^{-19} \mathrm{C}$.
3. The law of conservation of charge states that charge can neither be created nor destroyed, only transferred. Thus, the algebraic sum of the electric charges in a system does not change.

We now consider the flow of electric charges. A unique feature of electric charge or electricity is the fact that it is mobile; that is, it can be transferred from one place to another, where it can be converted to another form of energy.

## 电子代写|电路基础代写Circuit Fundamentals代考|Systems of Units

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$$600,000,000 \mathrm{~mm} \quad 600,000 \mathrm{~m} \quad 600 \mathrm{~km}$$

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## Matlab代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。