# Tag Info

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### Has anyone charged an object with 1 coulomb? Why was such a ridiculously large charge chosen as the unit of charge?

The underlying reason that 1 coulomb seems like a large amount of charge is that most charged particles in ordinary settings are nonrelativistic -- moving at speeds $v$ much less than the speed of ...

### Is there any truth to interpreting definition of a second as corresponding to oscillations?

The definition for the cesium clock is: 9192631770 cycles per second is frequency of the radio waves which cause maximum resonance, a physically measurable condition, in the cesium atoms. This ...
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### The definition of 1 kelvin

To answer this question it may help to take an example from a more familiar area of physics, and then discuss temperature. For a long time the kilogram (the SI unit of mass) was defined as the mass of ...

### How long is a second?

A second is a second long by definition, but if you measure any time in seconds, the number of seconds you infer will be subject to an error of at least $\mathcal O(10^{-15})$ because of the ...

### Do all equations have identical units on the left- and right-hand sides?

It depends what you mean by "unit". If you mean something like "seconds", then no. Counterexample: 1 minute = 60 seconds has different units on both sides, but they're both ...
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### Why is the length of the Kelvin unit of temperature equal to that of the Celsius unit?

Kelvins aren't really all that natural either; or rather, they are just as arbitrary as Celsius. You need another arbitrary quantity--the Boltzmann constant--to get the temperature unit to work with ...
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### Why is the Planck constant an exact number with defined value?

Planck's constant relates two different types of quantities, namely energy and frequency. That means it is a conversion factor which converts the units of quantities from one form to another. If the ...
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### What is a joule? I find the definition confusing

Maybe imagine the ball is being pulled by a weight, or a spring, back here on Earth. The weight falls down and pulls the ball along: It is easy to see that the weight goes down 1 meter when the ball ...

### Why is the prospective new kilogram standard a sphere?

There is a nice article in the New Scientist that describes how these spheres were made. Sphere can be made very precisely (and their shape measured accurately) simply because of their symmetry - and ...