# Tag Info

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### Help understanding quote on theory and knowledge in Gravitation (Misner, Wheeler, & Thorne, 2017)

In physics everything is a mathematical model. If you ask me what an electromagnetic field is I would answer it is that which is described by Maxwell's equations. If you ask me no, really, what is an ...

### Intuition for magnetic dipole moment

To understand why the area appears in the definition, we need to consider a rectangular current carrying wire with side lengths $a$ and $b$ in a magnetic field $B$ Using Lorentz's force, we know ...

### Intuition for magnetic dipole moment

You can notice that: $$\int d^2x = \frac{1}{2}\oint r\times dx \tag{1}$$ so you can rewrite your original definition as: $$m = \frac{1}{2}\oint r\times Idx$$ From there, the continuous formula is ...

### Help understanding quote on theory and knowledge in Gravitation (Misner, Wheeler, & Thorne, 2017)

That discussion in chapter 3 was so important to Misner Thorne and Wheeler that they revisited it in section 12.3 Point of principle: how can one write down the laws of gravity and properties of ...
1 vote

### Meaning of electric dipole moment

Imagine you have some irregular charged object and you want to know what will be the electric field it produces at some given point. What is your course of action? First, you can go brute-force and ...
1 vote

### Conditions for a force to be conservative - Does the second condition imply the first?

I think that the first sentence has the purpose of avoiding those forces that are explicitly dependent on time or velocity. For particular forces that still depends on time the second sentece could be ...
1 vote

### WKB method as a Semiclassical Approach

It is semiclassical since you use a gaussian wavepacket. The central point of such a wavepacket follows exactly the classical equation of motion. It is then called semiclassical since the central part ...
1 vote

### Why can the Ampere not be defined as the flow of $n$ Coulomb in $n$ seconds?

Mathematically , both are Equivalent. Practically , we might have Difficulties. There at least 3 Issues or flaws with your way. (1) When we say "n" , we are leaving it unknown. When I report ...
1 vote
Accepted

### Why can the Ampere not be defined as the flow of $n$ Coulomb in $n$ seconds?

That’s how it is defined, using the 1’s rather than the n’s. You’re not really missing anything about the math/physics of the situation. Yes your definition would indeed give the same result. It’s ...
1 vote

### What's the difference between observable and unobservable objects in a physical theory?

I think that this is an interesting question about Physics. However, to avoid crossing the border between Physics and Philosophy, it is better to put aside terms like exists, or existence. So, let's ...
1 vote

### What's the difference between observable and unobservable objects in a physical theory?

The question is really more philosophical than physical. Theories are designed to explain experimental observations, and very few things are available to direct measurement (and even less to human ...
1 vote

### What is meant by "inertial forces", in contrast to the "resultant force"?

What is meant by "inertial forces", in contrast to the "resultant force"? For example, in the Wikipedia page on Reynolds number it is said: The Reynolds number is the ratio of ...
1 vote

### Why hexagonal closed packed structure is not a Bravais lattice?

Hexagonal close packed (hcp) is one of the two simple types of atomic packing with the highest density, the other being the face-centered cubic (fcc). However, unlike the fcc, it is not a Bravais ...
1 vote

### Is the Lorentz force a vector field or just a vector?

The force pertains to a charged body moving along a trajectory given by the equation $𝐫 = 𝐑(t)$, where I'm going to denote the function by a separate letter to remove the confusion. The velocity is \$...
1 vote

### Nomenclature: Yang-Mills theory vs Gauge theory

The generic name is gauge theory. That includes any dynamics that has the gauge potential and gauge field strengths as its main players. Yang-Mills is a gauge theory whose dynamics are given by a Yang-...

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