# 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.

1,157 questions
Filter by
Sorted by
Tagged with
1k views

### Is the number 1 a unit?

In dimensionless analysis, coefficients of quantities which have the same unit for numerator and denominator are said to be dimensionless. I feel the word dimensionless is actually wrong and should be ...
948 views

### Why Counterclockwise starts from East?

In vector lessons, we have counterclockwise angle of rotation of the vector starts from East. "The direction of a vector is often expressed as a counterclockwise angle of rotation of the vector about ...
345 views

### In which direction should flow of electric current be taken while solving problems?

Consider a simple circuit with a battery of $\theta\ \text V$s, and two resistors of $R_1 \ \Omega$s and $R_2\ \Omega$s connected in series. Let us assume that $R_1$ is connected nearer to the ...
1k views

### Should we necessarily express the dimensions of a physical quantity within square brackets? [duplicate]

For example, should we write the dimension of mass, e.g. $\mathrm{kg}$ as $[M]$ or is it enough to write it as $M$?
181k views

### What is the sign of the work done on the system and by the system?

What is the sign of the work done on the system and by the system? My chemistry book says when work is done on the system, it is positive. When work is done by the system, it is negative. My physics ...
22k views

### What does “clockwise” mean, exactly? [closed]

I am in the middle of a discussion with a friend about the meaning of the term "clockwise". Wikipedia indicates that a clockwise rotation goes as top-right-down-left. However, my friend argues that "...
14k views

### Sign convention in optics

Why is the sign convention used in the derivation of the lens formula and yet used again when it is applied in numerical problems? Won't the whole idea of sign convention be eliminated if it is used ...
4k views

### Thermodynamic cycles, when is the work negative/positive?

ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is 'bendy'...
15k views

### Who (and Why) started the “electrons are negative, protons are positive” convention? [duplicate]

For some reason everyone labels electrons using a minus sign and protons using a positive sign, even though the opposite seems more intuitive: Who started the convention that electrons should be "...
74 views

### Is it incorrect to explain the direction of a coded vector quantity?

For example, let's say that in a linear physics problem, all the data are given to a certain direction, and coded positively for direction to the right. So +5m/s would be a velocity of 5m/s to the ...
734 views

### What is wrong with this form of the Maxwell-Faraday equation?

What is wrong with this form of the Maxwell-Faraday equation? $$\oint \vec{E}\ \partial \vec l= \bigcirc \hspace{-1.4em} \int \hspace{-.6em} \int \frac{\partial \vec B}{\partial t}$$ "Line integral ...
879 views

### How to reconcile the two definitions of work? (mechanical and thermodynamical)

When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$. However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$. I'm having trouble ...
286 views

48k views

### How can you have a negative voltage?

How can you have a negative voltage? I don't really understand the concept of negative voltage, how can it exist?
603 views

### Can the overall sign of the Minkowski metric be changed?

If we take the Minkowski metric, $\eta_{\mu\nu}=(1,-1,-1,-1)$, instead of the usual $(-1,1,1,1)$, does this change the form of the Lorentz Transform? I think the standard Lorentz Transform looks like: ...
134 views

### When are leap seconds added in various time zones?

I understand that technically when a leap second is added, it is added after midnight UTC, but I'm unclear how the addition is handled in other timezones. For precise reckoning of course (e.g. ...
3k views

### Levi Civita Symbol and contravariance vs covariance

I have a question regarding the Levi-Civita symbol and contravariance vs covariance. Some of this was asked in a previous post, but I think I need more clarification. Consider the magnetic field: \...
7k views

### What is the difference between UT0, UT1 and GMT time?

Every reference I find says that they are "essentially" the same, which we all know really means that they are not the same, but different only by a some small amount that someone else other than me ...
5k views

### Why are different frequency bands used in different countries?

Why are different frequency bands used in different countries despite ITU's effort for a common frequency band use? There's got to be a reason behind this. For instance, U.S.-based Verizon Wireless ...
4k views

### Mutual Inductance and the Dot Convention

Can anyone please explain me, the dot convention in coil systems (Mutual and self inductance) with some related images to understand..?
1k views

6k views

### Which one true in First law of thermodynamics: $Q = \Delta U \pm W = \Delta U \pm p\Delta V$ or $\Delta U= \Delta Q + \Delta W$?

Which one true in First law of thermodynamics: $Q = \Delta U \pm W = \Delta U \pm p\Delta V$? (where $\Delta U$ is change of internal energy, $W$ work made by system and $Q=cm\Delta T$ heat made by ...
706 views

### What's the common consensus on the meaning of “physical change”?

I'm doing a textbook problem that shows a "molecular level" view of some matter, little colored balls, before and after, and there are, among the four questions, two that say: 1) Did a physical change ...
85 views

### Is this phase right?

Hello at physics lectures we wrote a phase of a sine wave like this: $$\phi = kx - \omega t$$ Is this right? As I recall the phase of a wave should be written like this: $$\phi = \omega t - kx$$ ...
12k views

### When an object moves downward, is its height negative? [closed]

The question is: A ball is thrown directly downward with an initial speed of 8.00m/s from a height of 30.0m. After what time interval does it strike the ground. So I went through the problem and ...
103k views

### Thermodynamics - Sign convention

I use the sign convention: Heat absorbed by the system = $q+$ (positive) Heat evolved by the system = $q-$ (negative) Work done on the system = $w +$ (positive) Work done by the system = $w -$ (...
4k views

### Why is the partition function called ''partition function''?

The partition function plays a central role in statistical mechanics. But why is it called ''partition function''?
1k views

### Levi-Civita symbol in Euclidean space

Suppose a component of tensor field is described by $B^k=\varepsilon^{kij} \phi_{ij}$. If we define $B^k$ in an Euclidean space then does the rising or lowering of the indices of the Levi-Civita ...
4k views

2k views

### Why do we still not have an exact (constants-based) definition for a kilogram?

I read that there is an effort to define a kilogram in terms that can exactly be reproduced in a lab. Why has it taken so long to get this done? It would seem this should be fairly important. Edit: ...
2k views

### Conversion of the units BeV (US) and GeV (UN)

What is the difference in the definition of a billion electron volts in United states (US) and United Nations (UN)? When the US people say billion, do they mean $10^{12}$ or $10^9$?
2k views

### Why is 'the period' marked as letter T?

I'm not a native English speaker and I was wondering, why 'the period' got the letter $T$. I've asked myself the question when I was thinking about stuff related to the frequency. I.e.: $f$ - ...
4k views

### What is the origin of the naming convention for position functions?

In physics, position as a function of time is generally called $d(t)$ or $s(t)$. Using $d$ is pretty intuitive, however I haven't been able to figure out why "s" is used as well. Is it possibly based ...
2k views

### How is Planck's law defined?

Now, I found three different definitions of Planck's law: $$P_1(\nu,T) = \frac{8 \pi}{c}\frac{h \nu^{3}}{c^2} \frac{1}{e^{h\nu/kT}-1}$$  P_2(\nu,T) = 2\frac{h \nu^{3}}{c^2} \frac{1}{e^{h\nu/kT}-1}...
I'm a bit embarrassed, but I'm not able to compute the electric potential at point $P$ (at a distance $R$ from the origin) generated by a positive unitary point charge in the origin with the right ...