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1500 questions
35
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3 answers
Why is the light reflected at the same angle from mirror?
From the school physics I know that the material objects bounce from the plane surface at the same angle, losing some kinetic energy. In the same school I was taught that the light (and waves in general) obeys this principle too.
Obviously, in the…
abyss.7
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35
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2 answers
Symbols of derivatives
What is the exact use of the symbols $\partial$, $\delta$ and $\mathrm{d}$ in derivatives in physics? How are they different and when are they used? It would be nice to get that settled once and for all.
$$\frac{\partial y}{\partial x}, \frac{\delta…
Steeven
- 50,707
35
votes
3 answers
Quantum entanglement faster than speed of light?
Recently I was watching a video on quantum computing where the narrators describe that quantum entanglement information travels faster than light!
Is it really possible for anything to move faster than light? Or are the narrators just wrong?
Vineet Menon
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35
votes
11 answers
Recommended books for advanced undergraduate electrodynamics
What books are recommended for an advanced undergraduate course in electrodynamics?
A.khalaf
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35
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4 answers
How can area be a vector?
My professor told me recently that Area is a vector. A Google search gave me the following definition for a vector:
Noun: A quantity having direction as well as magnitude, esp. as
determining the position of one point in space relative to…
Green Noob
- 1,027
35
votes
5 answers
Is it possible to focus the radiation from a black body to make something hotter than that black body?
My previous question wasn't specific enough. I'll try to be more specific.
Let's imagine we have a hot body let's say 6000K hot that emits lots of thermal radiation. Let's assume 1kW of radiative power falls on on a m². Now if we use a lens with 1m²…
Calmarius
- 8,100
35
votes
7 answers
What is the difference between diffraction and interference of light?
I know these two phenomena but I want to know a little deep explanation. What type of fringes are obtained in these phenomena?
35
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4 answers
The physical definition of work seems paradoxical
So this is possibly a misunderstanding of the meaning of work, but all the Physics texts, sites, and wiki that I've read don't clear this up for me:
In the simplest case with the simplest statement, work is force times distance. If you push with a…
Addem
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35
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16 answers
What does a wing do that an engine can't?
This isn't a question of how a wing works -- vortex flow, Bernoulli's principle, all of that jazz. Instead, it's a question of why we need a wing at all. A wing produces lift, but why is that necessary?
I got to this by thinking of an airplane at a…
yshavit
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35
votes
2 answers
Are the fast axes on Thorlabs quarter-waveplates mislabeled?
Some members of my lab are performing a polarization-sensitive experiment where they need to use a quarter-waveplate (QWP) with the fast axis in a specific direction. In the process of carefully checking all the polarization optics, they discovered…
ARM
- 870
35
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2 answers
Energy-Momentum Tensor in QFT vs. GR
What is the correspondence between the conserved canonical energy-momentum tensor, which is $$ T^{\mu\nu}_{can} := \sum_{i=1}^N\frac{\delta\mathcal{L}_{Matter}}{\delta(\partial_\mu f_i)}\partial^\nu f_i - \eta^{\mu\nu}\mathcal{L}$$ (the four…
PPR
- 2,004
35
votes
2 answers
Difference between regularization and renormalization?
In quantum field theory we have the concepts of regularization and renormalization. I'm a little confused about these two. In my understanding regularization is a way to make divergent integrals convergent and in renormalization you add terms to the…
Apogee
- 1,268
35
votes
5 answers
Is the graviton hypothetical?
Wikipedia lists the graviton as a hypothetical particle. I wonder whether graviton is indeed hypothetical or does its existence directly follow from modern physics? Does observation of gravitational waves amount to the discovery of graviton or could…
Anixx
- 11,159
35
votes
2 answers
What does it mean that there is no mathematical proof for confinement?
I see this all the time* that there still doesn't exist a mathematical proof for confinement. What does this really mean and how would a sketch of a proof look like?
What I mean by that second question is: what are the steps one needs to prove in…
Physics_maths
- 5,559
35
votes
7 answers
Why does a system try to minimize potential energy?
In mechanics problems, especially one-dimensional ones, we talk about how a particle goes in a direction to minimize potential energy. This is easy to see when we use cartesian coordinates: For example, $-\frac{dU}{dx}=F$ (or in the multidimensional…
user35734
- 775