Joules units

$E=hv$

Jedrick Zablan 3L
Posts: 68
Joined: Sat Aug 17, 2019 12:17 am

Joules units

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

andrewcj 2C
Posts: 87
Joined: Thu Jul 11, 2019 12:17 am

Re: Joules units

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.

KaleenaJezycki_1I
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Re: Joules units

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.

Jenna Ortiguerra 4G
Posts: 50
Joined: Sat Aug 17, 2019 12:18 am

Re: Joules units

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.

505106414
Posts: 55
Joined: Wed Sep 18, 2019 12:17 am

Re: Joules units

So the units are essentially equivalent to each other?

Nathan Nakaguchi 1G
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Re: Joules units

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.

Mai V 4L
Posts: 55
Joined: Fri Sep 28, 2018 12:23 am

Re: Joules units

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