Planck's Constant

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nathansalce 3e
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Planck's Constant

Postby nathansalce 3e » Sat Oct 14, 2017 7:10 pm

Can somebody explain to me why Planck's constant is measured in Joule Seconds. What is the significance of this unit and how does it relate to the equations its involved in? I originally thought Planck's was in joules per second, but was mistaken when i later discovered the truth. I am trying to find better ways to remember this unit of measurement.

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Re: Planck's Constant

Postby Chem_Mod » Sat Oct 14, 2017 8:21 pm

Planck’s constant relates the energy of light to its frequency (E=h*v). Energy is measured in Joules, while frequency is measured in Hz (or s-1). Thus, in order for units to cancel, h must be J*s. Planck’s constant was derived by comparing energy to frequency.

Rachel Formaker 1E
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Re: Planck's Constant

Postby Rachel Formaker 1E » Sat Oct 14, 2017 8:22 pm

Constants usually have the units that they do because of the units of the quantities that they relate.
So in the equation E=hv, Planck's constant relates frequency(in seconds-1) and energy (Joules). In order for this equation to make sense, Planck's constant must have the units of Joule-seconds.

Haocheng Zhang 2A
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Re: Planck's Constant

Postby Haocheng Zhang 2A » Sun Oct 15, 2017 12:53 pm

For a formula, the units of both sides of equation should be same. For example, v = at, the unit of accerleration is "m*s^-2", the unit for t is "s", for a*t, the unit is m*s^-1, which is same as the unit of velocity. For E = hv, the unit of E is joules, the unit of v(frequency) is s^-1, so the unit of h have to be joules seconds for both sides of equation have same units.

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