# Tag Info

1

In terms of radiography / radiology, kVp is the tube voltage / tube potential between the cathode and the anode, set by the operator. The unit eV (or keV as used in the range of general radiography, MeV as used by Radiation Therapy) describes the energy of the particles - in this case, the electrons in the x-ray tube, and the x-ray photons coming off the ...

1

The kilogram is the base unit of mass because electrical engineers in the late 19th century chose a particular set of practical electrical units. These practical units were a success, and we are still using them today: ohm, volt, ampere, and the joule. In 1874 the mechanical units cm, g, s ('CGS') were adopted as the coherent system of units for science. ...

0

An attempt at a REALLY simple answer: 1. Can we raise one unit to the power of another unit? No. 2. How do we know that there aren't more base units? A base unit is defined whenever it is needed. If I am dealing with length, I want to define a base unit for length, which is arbitrary. Once the base unit for length is agreed upon (e.g., the meter), ...

1

I will answer question 3 since I noticed 1 and 2 have been answered nicely. How are we sure that $\rm m$ for example is a base unit and is not made up from other units? We know that $\rm m$ is a base unit because we defined it as a base unit. Namely, we defined it as the base unit of length. Is this confusing? Look at it in a different way. You ...

1

It means that at lower energies the electromagnetic force dominates, and the gravitational effects are barely noticeable if not negligible. If you want to actually test gravity on a microscopic scale in a system that is also subject to electromagnetism (eg charged particles) you have to reach high enough energies for the two forces to be roughly equal in ...

2

An attempt at a simpler answer: No. Remember that the symbol for a unit does not represent a number/variable in any sense. It is a label we put on a number to say what the number is "counting". So just as $3^\textrm{penguin}$ doesn't mean anything (penguins can be counted to give numbers, but the word "penguin" is a label, not a number) you can't raise ...

5

No. If we could we could raise a unitless quantity to another unit, hence $e^x$ where $x$ is unitful. We have no idea how we would define that except by the old trick of pretending that the power series $\exp(x) = 1 + x + x^2/2 + \dots$ applies equally well when $x$ is unitful -- but that's an obvious type error, hence we just don't know how to do it. ...

Top 50 recent answers are included