### Joules units

Posted:

**Fri Oct 18, 2019 12:39 am**Hello can anyone explain to me why Joules in Planck's Constant is kg x m^2 x s? Thanks.

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=15&t=47889

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Posted: **Fri Oct 18, 2019 12:39 am**

Hello can anyone explain to me why Joules in Planck's Constant is kg x m^2 x s? Thanks.

Posted: **Fri Oct 18, 2019 1:34 am**

In the formula E = hv, E is measured in Joules and v is measured in Hz, or s^-1. By dimensional analysis, we see that by multiplying kg x m^2 / s by 1/s, we get a units of kg x m^2/s^2. Since Joules is a measure of energy/work, it is equivalent to force x distance. Breaking this down further, force is equivalent to mass x acceleration, which results in units of kg x m/(s^2). Multiplying this by distance gives you kg x m^2/s^2, which is the same as the units for the right side of the E = hv equation.

Posted: **Fri Oct 18, 2019 9:21 am**

JedrickZ_3L wrote:Hello can anyone explain to me why Joules in Planck's Constant is kg x m^2 x s? Thanks.

Joules in Planck's Constant is expressed as such because it helps for unit cancellation, depending on what you are solving for one of these two expressions will be easier to visually see how you obtain your final units.

Posted: **Sat Oct 19, 2019 7:42 pm**

Joules in Planck's Constant can either be expressed by 6.626 x 10^-34 J.S. or 6.636 * 10^-34 kg*m^2*s^-1. Typically, choosing between 6.636 * 10^-34 kg*m^2*s^-1 and 6.626 x 10^-34 J.S. is situational, in which the one that would provide the easiest cancellations would be the best option to use.

Posted: **Thu Oct 31, 2019 9:53 am**

So the units are essentially equivalent to each other?

Posted: **Thu Oct 31, 2019 10:18 am**

Planck's Constant's units are J * s (joules times seconds) not necessarily just joules, thats why the Planck's units are (kg m^2 s^-2) * (s) = kg m^2 s^-1.

Posted: **Sun Dec 08, 2019 9:15 am**

Does anyone have a video they think is aa good reference for this topic?