Please tell me about the electromagnetic field formula

深圳小花

Please tell me about the electromagnetic field formula [Copy link]

 

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I would like to ask what is the difference between 1 and 2 in the following formula, and how the three terms on the right side of the formula are derived? I don’t understand, so please explain it to me.

maychang

What is the difference between 1 and 2 in the following formula?

(1) is a function, (2) is a partial derivative.

If you don't understand this, you need to go back and look at ordinary differentials and partial differentials.

chunyang

The OP should think clearly about what purpose he wants to achieve. Such "learning" will not produce any positive results.

深圳小花

chunyang posted on 2021-12-27 20:06 The OP should think clearly about what he wants to achieve. Such "learning" will not produce any positive results.

I just want to learn about electromagnetic fields

深圳小花

chunyang posted on 2021-12-27 20:06 The OP should think clearly about what he wants to achieve. Such "learning" will not produce any positive results.

How did you come up with the

part?

深圳小花

maychang posted on 2021-12-27 09:49 "What is the difference between 1 and 2 in the following formula?" (1) is a function, (2) is a partial derivative. If you don't understand this, you have to go back and look at the constant derivative...

Please ask

How did this part come about?

maychang

Shenzhen Xiaohua published on 2021-12-28 09:43 May I ask how this part came out?

You need to first clarify the content in the square brackets of this picture, not the content in the red box you marked.

To understand the contents in the square brackets, you need to first look at the following figure:

This picture is copied from Tongji University's Advanced Mathematics, sixth edition, page 116. You have this book in your hands.

The above is the differential of an independent variable, that is, y is a function of an independent variable x.

Understand the relationship between the quantities in the above figure, and then look at the definition of the differential of functions of multiple independent variables, that is, partial differential, and you can understand the contents in the square brackets.

maychang

Shenzhen Xiaohua published on 2021-12-28 09:43 May I ask how this part came out?

Before you understand ordinary differentials, you are already looking at partial differentials of multiple independent variables. Learning cannot be done in a jumpy way.

Chunyang is right: there will be no positive results from "learning" in this way.

maychang

Shenzhen Xiaohua published on 2021-12-28 09:43 May I ask how this part came out?

If you understand the contents of the 7th floor picture, but still don't understand the contents of the square brackets in the first post, please look at the picture below. This picture is copied from Tongji University's "Advanced Mathematics" Volume 2, page 71

The red line is the total differential. This equation has two terms, each of which is the form of the partial derivative multiplied by the increment of the independent variable, which is the form of the second term in the square brackets you asked about. After understanding the meaning of the red line in the above figure, think about what the first term in the square brackets (function value) plus the partial derivative multiplied by the increment of the independent variable means.

maychang

Shenzhen Xiaohua published on 2021-12-28 09:43 May I ask how this part came out?

If you still don’t understand, then you need to think about the geometric meaning of the second red box (i.e. partial derivative).

maychang

Shenzhen Xiaohua published on 2021-12-28 09:43 May I ask how this part came out?

If you don’t understand the geometric meaning of partial derivatives, you should think about the geometric meaning of (constant) derivatives, which is the geometric meaning of the figure on the 7th floor. This is the most basic content of differential calculus.

深圳小花

maychang posted on 2021-12-28 10:57 Ordinary differentials have not been figured out yet, but we are already looking at partial differentials of multiple independent variables. Learning cannot be done in such a jumpy way. Chunyang said it correctly: so &ldq ...

Thank you. I have learned all of them, but I didn't understand them at the time, and I didn't learn them well. Now I am checking for gaps and filling them in.

maychang

Shenzhen Xiaohua published on 2021-12-28 14:13 Thank you. I have learned it all, but I didn’t understand it at the time. Now I am checking for deficiencies and filling in the gaps.

If you don’t understand the content in the picture on the 7th floor, then it is not a matter of “checking for gaps and filling them in”, so you should retake this course.

chunyang

Shenzhen Xiaohua published on 2021-12-28 09:41 I just want to learn about electromagnetic fields

"Thinking" can be a lot. Realizing it is another matter. If you want to achieve your goal, you should first understand yourself, so that you can find the right path. But from your question, you are far from understanding yourself, so the ending is predictable.

深圳小花

maychang posted on 2021-12-28 14:45 If you don’t understand the content in the picture on the 7th floor, then it is not a problem of “checking for gaps and filling them in”, you should retake this course.

Thank you for your advice. I feel like I have never learned anything.

深圳小花

chunyang posted on 2021-12-28 15:25 "Thinking" can be a lot. To achieve it is another matter. If you want to achieve your goal, you should first understand yourself, so that you can find...

Thank you. You are right. I feel like I am at the level of a junior high school student. Oh, it is so hard to learn something. Most people would have given up long ago. Oh. Fortunately, although my brain is not working well, I can't stay idle.

chunyang

Shenzhen Xiaohua published on 2021-12-28 17:32 Thank you. You are right. I feel like I am at the level of a junior high school student now. Oh, it is so hard to learn something. Most people would have given up long ago. Oh, oh, so...

Real learning requires methods. You can’t learn for the sake of learning. That’s just pretending to fool yourself. You might as well learn how to learn first.

深圳小花

chunyang posted on 2021-12-29 15:09 To truly "learn", you must pay attention to the method. You can't "learn" for the sake of learning. That's just pretending to fool yourself. Why not first learn how to "...

Thank you very much. Then may I ask how to learn it?

chunyang

Shenzhen Xiaohua published on 2021-12-30 08:31 Thank you very much. Then please tell me how to learn how to learn?

First, know yourself and start from the most basic level. The most important thing is to learn logical thinking. This is the problem to be solved when learning Euclidean geometry, and it is also the reason why Euclidean geometry is the foundation of all mathematical and scientific subjects.

深圳小花

chunyang published on 2021-12-30 15:18 First, recognize yourself and start from the very beginning. The most important thing is to learn logical thinking. This is the problem to be solved when learning Euclidean geometry, and it is also for...

Thank you. You mentioned a logical question. I would like to ask, if there is a Jacky Cheung in China, and if there is a singer in Korea who only sings Korean songs and has a similar status to Jacky Cheung, the number of his albums and his popularity in Korea are the same as Jacky Cheung's popularity in China.

I would like to ask, China's Jacky Cheung's singing income is 28 times that of the Korean singer. Do you think this is normal?