# Questions tagged [conventions]

A convention is a set of agreed, stipulated, or generally accepted norms. It typically helps common efficiency or understanding but is not required, as opposed to a strict standard or protocol.

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### Arbitrarity of $i$ in the propagator

My question is simple: how arbitrary can the factor in front of the propagator be? What I mean by that is, if we call the wave operator $K$ and the propagator $G$, I've seen different books use ...
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### Sign Convention in Ray Optics

While solving questions on Refraction due to 2 spherical surfaces the sign of the image formed after the first refraction (here at '$A$') depends whether the image formed is towards left or right side ...
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### What is parity useful for in physics?

What do we gain by defining the parity of different objects in physics? I can learn that $L$ (angular momentum) has the opposite parity as $p$ (linear momentum) or $B$ (magnetic field) hass opposite ...
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### What is a rigorous and general definition of the parity operator?

Is there a rigorous definition of the parity operator? I see parity come up in the context of angular momentum, magnetic fields, quantum spin/particles. It is also related to the Levi-Civita symbol vs ...
1 vote
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### Why are most solar panel rated at 12 volts or 24 volts? [closed]

Most solar panel come in 12 volts or 24 volts, why?
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### Fourier Transform of a Wave Packet [closed]

In the analysis of coherence and interference, I encountered the following expression: $$F(t)=\Re\int_0^\infty\mathrm d\omega e^{-i\omega t}H(\omega)$$, where $\Re$ denotes the real part of the ...
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### Why does the Strange Quark have Strangeness -1?

I have been trying to find an explanation for the strange quarks negative strangeness value, I understand the term strangeness predates the quark model, but I'm unsure if terminology carry over is the ...
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### Covariant vs. contravariant definition of the Energy-Momentum tensor

I have a question regarding the definition of the energy-momentum tensor. I've seen it defined as a (2,0) tensor, so it has 2 upper indices $T^{ab}$, but many times it is written as a (0,2) tensor ...
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### When defining a coordinate system, does it matter if it is right- or left-handed?

When you are defining a coordinate system when solving a problem, do the coordinates need to be right-handed to obtain a correct solution? I feel like the answer is no because the directions of ...
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### Energy Momentum Tensor for massive Real Scalar Field in GR with metric signature (+ - - -) [duplicate]

I wanted to calculate the Energy Momentum Tensor for the massive real scalar field in Kerr Background. But instead of the usual (- + + +) metric signature, I have to use the (+ - - -) signature for ...
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### Why electrical current is base quantity instead of electrical charge? [duplicate]

I thought base quantities are defined as independent quantity. But I realized Electrical Current which usually notated as I for ...
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### Is my book drawing a vector wrongly?

My book's drawing: According to my book, $\underline{u}=\vec{AB}$. However, my book hasn't put the arrow at the end of the line segment $AB$, but rather my book has put the arrow at the middle of $AB$...
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### Why were electrons chosen to be negatively charged? [duplicate]

Wouldn't it make more sense to call electrons positively charged because when they move they make electricity?
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### Vector symbols confusion: A vs |Ā| when it comes to representation of magnitude of vectors

My teacher said that $\vec{A} = \left| \vec{A} \right| \hat{A}$ , where $\left| \vec{A} \right|$ is the magnitude and Â is the direction of the vector. In this homework question, what exactly do you ...
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### Is $\Delta$ notation commonly used for the difference in a quantity between two objects? [closed]

In a standard Atwood machine, the acceleration is $$a = g\dfrac{m_1 - m_2}{m_1+m_2}.$$ Would writing this as $$a = g \dfrac{\Delta m}{M}$$ where $M$ is the total mass be an abuse of notation to most ...
1 vote
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### Why is the Fermi Constant sometimes listed in units of 'joule metre$^3$'? How is that related to its normal units of GeV$^{-2}$ or J$^{-2}$?

Normally, the Fermi Constant is valued as $1.1663787\times10^{-5}$ GeV$^{-2}$ or its equivalent in Joules. But on Rampfesthudson and Oxford Reference, it says, $1.435\times10^{-36}$ joule metre$^3$ I ...
1 vote