EM Physics Exam 1

考完离散数学和线性代数,下一周还要考电磁学。因为这学期选课失误,选到的教授讲的课太烂了,所有东西都必须要自学,光是写作业满足不了我的求知欲考试的需求。不好好复习怕是不能维持我一砖一瓦建立的好学生形象!要边学边复习,我太难辽。

我太难了

第一轮复习

先进行的第一轮复习由做复习题开始,然后归纳一下产出不会做或者有疑问的地方,接着一个个解决。

步骤

  1. 写完 Practice Exam
  2. 归纳错题和有疑问的题
  3. 逐个解决
  4. 小结

错题集和疑问

Part 1

Part 1 mainly covers:

  • Coulomb’s Law
  • Electric Field
  • Gauss’s Law
  • Electric Potential
Part 1 Problem 7

Question: I can deal with this problem, but why exactly?

Solution: There are two ways to solve this problem:

  1. Electric potential is the integral of electric field in respect of the path. Therefore, the rate of change of electric potential over a path is electric field. Consider a function with a value of zero but a flat slope \to electric potential and electric field can be both zero.

    ΔV=abEdl\Delta V=-\int_a^b\vec{E}\cdot d\vec{l}

  2. Consider two identical point charges separated by a distance. Since the electric field is going to the opposite direction with the same magnitude right between the center of two charges, the net electric field goes to zero. However, by scalar addition, the point has a non-zero electric potential.

    Example 1

Part 1 Problem 8

Question: same as above.

Solution: there are two way of solving this problem.

  1. Same as above, but the other way around:

    dV(l)dl=E(l)\frac{dV(l)}{dl}=E(l)

  2. Consider two point charges with opposite signs and the same magnitude of charges. Since the electric field is going to the same direction with the same magnitude right between the center of two charges, the net electric field is non-zero. However, by scalar addition, the net electric potential is zero since they have the same magnitude but opposite signs.

    Example 1

Part 1 Problem 9

Issue: I got it intuitively, but got the answer wrong because of the sign.

Solution: Read the question carefully and check the sign of charges carefully.

Part 2

Part 2 covers:

  • Circuits
    • Resistors
      • Resistivity
    • Capacitors
    • Power
Part 2 Problem 2

Issue: I got it correctly, but I was confused by option C since I got the way of adding capacitance incorrectly.

Solution: Review.

In series: 1C=1C1+1C2++1Cn\frac{1}{C}=\frac{1}{C_1}+\frac{1}{C_2}+\dots+\frac{1}{C_n}

In parallel: C=C1+C2++CnC=C_1+C_2+\dots+C_n

Part 2 Problem 9

Issue: I accidentally put diameter as radius in calculation.

Solution: Do problems in O+P - Solve way.

小结

总的来说其实 Kiyoshi 没有犯犯很严重的问题,大概题都能找到解决方案。反而概念性的简单的小问题容易犯错。总的来说还是对于电势和电场方面的基础知识不够牢靠。

第二轮复习

To - Be - Done

文章作者: Takahashi Kiyoshi
文章链接: https://blog.k1yoshi.com/article/em-phys-exam-1/
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