# Whats a joule second?

1. Jul 9, 2010

### cnidocyte

I can easily picture joules per second (I just see light of varying intensities passing a point at varying rates) I don't know what a joule second is. I know that Plancks constant is just to use the frequency of the photon to find out its energy but what in the name of God is a joule second?

2. Jul 9, 2010

### dulrich

It is the unit of action -- as in the least action principle.

It is also the unit of angular momentum -- cf. the Bohr atom.

3. Jul 9, 2010

### Staff: Mentor

A joule in mechanical work is 1 N of force applied on an object to move it a distance of 1 m. So a joule persecond is doing the above action in one second.

Btw, a "joule per second" and a "joule second" are not the same thing. Jule per second is dividing by seconds, joule second would be multiplying by seconds.

4. Sep 14, 2010

### 0xCACA

If i understood correctly you can consider this example:

you can boil 1 m^3 of water by transferring to it N*dE energy in a 1 second OR
you can boil 1 m^3 of water by heating water N*dt time with 1 joule of energy

and thus we can define minimal action needed for 1 m^3 water to be boiled -
N*dE*dt

As about Plank constant we can interpret it also like this:
you can't transfer less energy than h in 1 second OR
you can't transfer 1J of energy in less than h seconds.