Is current a scalar or a vector?Will high school and college teach conflict?
Every time I post related topics, some students argue in the comments section, such as “our physics teacher said that electric current is a scalar in high school, but a vector in college”, or “sometimes electric current is a scalar, and sometimes it can be treated as a vector”…Let’s set the record straight today.The conclusion is in the last paragraph of this article!You can ask the physics teachers around you, you should see their gradually distorted expressions…① Viewpoint 1: According to the definition of current: I=q/t, q and T are both scalar, so I is obviously a scalar!In addition, the typical characteristic of vectors is that “the synthesis law meets the parallelogram rule”, and the current of two wires, no matter what the Angle between the wires is, will eventually converge at I1+I2, which obviously does not meet the parallelogram rule, so it also shows that the current is a scalar.Even if, according to Ohm’s law, I=U/R, the voltage U and the resistance R are scalars, the current cannot be a vector.Kunge comments: The above content, is any high school physics teacher will tell you, so it does not bring new information.② Viewpoint 2: The micro expression of current I=neSv, where velocity V is a vector, which means I should be a vector!Kunge solution: we are going to discuss this formula.First of all, there is a physical quantity in the formula “current density vector J= NEv”, which is not learned in high school but only taught in college. This quantity is used to describe the strength and flow direction of the current at a certain point. It is a vector (direction is the direction of the current at this point, namely the movement direction of the positive charge).For an ideal thin wire, a single amount of current (current strength) is sufficient.However, for more complex details such as the conduction of a large conductor and the spatial distribution of the current, the quantity of current intensity is not enough to explain clearly, so the “current density vector” needs to be introduced.Current density vector With “current density vector” this physical quantity, we will understand the micro expression of current “I=neSv= NEv ·S”, the integral form is (dot product of two vectors oh), namely: the current through a section is “the flux of current density vector through the surface”.In human terms – electric current is similar to magnetic flux in that it is a kind of “flux”. Electric current is the flux of the current density vector.Magnetic flux is a scalar quantity and electric current is a scalar quantity.Flux is a scalar quantity.Flux is all scalar ③ Point 3: According to the definition of ampere force “F=IL×B” (cross product of vectors).The current I is a vector. The current I is a vector. The current I is a vector.Strictly speaking, the differential form of the ampere force is dF=Idl×dB, here is the current element “Idl” into a vector, the direction of the current element is the direction of the current.Therefore, the vectorality of “current I” is not used here, let alone the current I in this formula is a vector.(4) Viewpoint 4: I am a college student, and it is clearly written in our electrical engineering textbook “current phasor (plural form)”. Why do you high school teachers think that “current must be scalar”?University electrical engineering teaching material: plural form of “current phase kun elder brother answer: in electrical engineering, characterization sine quantity is used in the plural, such as” voltage phase “, “current phase”, “electromotive force phase” and so on.The use of a complex number for current is a mathematical convenience (sinusoidal operations can be reduced to phasor operations).It’s like when we study the earth’s revolution and think of it as a mass, when it’s obviously not.Therefore, can not be based on “university electrotechnics teaching material current, voltage processing into a plural form of phasor”, on the wrong “to university, current, voltage is a vector”!Mathematical techniques do not disprove its physical nature.Conclusion: When we talk about “current” in the future, we should first distinguish whether you mean “current intensity I”, “current density vector J”, or “current element IdL”.In terms of the conventional electric current (I=q/ T, I=U/R) that most high school students ask about, it is a scalar — inextricable in high school and even in college!