# Tag Info

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The flux to which the jansky refers can be in any form of energy. It was created for and is still most frequently used in reference to electromagnetic energy, especially in the context of radio astronomy. The brightest astronomical radio sources have flux densities of the order of one to one hundred janskys. For example, the Third Cambridge Catalogue of ...

0

It means that your router has been reprogrammed to output a 58% stronger signal, given the same physical set-up this means that the signal that reach your computer is also 2 dB stronger. Note that this boost is only one way, your computer is still sending with the same power it used to. Depending on your hardware the reception may in general be better in one ...

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Let me assume your internet speed is the power of the router, divided by the square of the distance from the router (as the signal is spread over the surface of a sphere with area $4\pi r^2$). $$\text{speed} \propto \frac{P}{r^2}$$ Your power increased by $2\,\text{db}$ - this means a fractional increase of $(10^{1/10})^2 \approx 1.6$. With your new router ...

1

decibels are a scaling factor rather than a linear increase, so +2dB means the signal is *1.58 larger. +4dB would be *1.58*1.58 bigger. 2dB is a small increase, but may be just enough to improve your signal to improve your internet connection. More dB may not always give an improvement in the same way as if you stand right next to the loud speakers at a ...

0

This is a very interesting question. I don't know if there is a general and definitive answer, but I'll try to make some comments. I apologize if this ends up rambling; I'm finding this out as I write this answer. Operators have dimensions, since their eigenvalues are physical quantities. For bras and kets it gets more complicated. First, you cannot in ...

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Really good question. Measurements have unit but in quantum mechanics, a measurement is the "evaluation" of an observable on a state (or a state on an observable) something like $$\left\langle \psi | A | \psi \right\rangle ,\quad \psi\in\mathcal{H},\ A\in\mathcal{B}(\mathcal{H}) \ \text{self-adjoint}$$ A priori, there seem to be an arbitrariness in the ...

0

In SI units, electric charge is a fundamental quantity of nature. All the SI electrical units contain at least one factor of the "base" electrical unit. (This base unit is currently the ampere, but will soon become the coulomb.) The SI unit of resistance is $$\Omega = \rm \frac{V}{A} = \frac{J/C}{C/s} = \frac{J\,s}{C^2}$$ In CGS units, charge is not a ...

0

It is a fairly good question. Physical quantities don't have dimensions. They have one or more scales, and it is the scales that have dimensions. It is perfectly legitimate to set $\epsilon=\mu=1/c$, which would mean that the unit of charge $Q^2 = \text{Joule-seconds}$. This would derive for the fps system, $1\ \text{verber} = \frac{1}{94.55}\ ... 0 The easiest way is to add factors of$\hbar$and$c$as needed. For instance you can measure energy in$eV$(electron volts). And then you measure mass in units of$eV/c^2$, for instance you can say the mass of an electron is$511\times 10^3eV/c^2$. And for other units you also measure them as some power of eV multiplied by some power of$c$and some ... 0$\hbar=c=k_B=1$is what we normally refer to as natural units in particle physics. If we additionally set$G=1$we are ending up with only dimensionless quantities. Sticking with the first case, we have one unit to choose left . Normally, one chooses the unit of energy to be$[E]=eV$electron volts. From$c=1$for instance we know that time and length now ... 2 The units of$\hbar$are in fact J.s/rad. (thanks AV23) this is because$\hbar = \frac{h}{2\pi}$the units of h are J.s and the units of$\pi\$ are rad. Thus we have J.s/rad. (thanks Noiralef) Thus the ladder operators are in fact unitless. On reflection this is the only logical possibility as they move between different eigenstates - which must all be in ...

1

The stroboscopes we had at school, in a largely pre-electronic age, were simply rotating discs with a hole near the edge. You shone a light at the edge, and the RPM of the disc determined how rapidly the strobe would flash (as the hole passed in front of the light).

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It comes from the fact that most strobes are, or were, used to examine car engines. Specifically the distributor. Hence RPM

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