What is the Planck's Constant?

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The Planck's constant \( h \) is a physical constant that appears in equations whenever the equation describes quantum phenomena. For example, it appears in the light quantum hypothesis:

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In this equation Planck's constant connects the energy \( W_{\text p} \) of a photon (light particle) with the light frequency \( f \). From this equation you can also read the unit of the Planck's constant, if you rearrange the equation for \(h\): Js (Joule seconds).

You can measure the value of the Planck's constant, for example, using the photoelectric effect. It has the value:

Value of the Planck constant
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A straight line in the energy-frequency diagram results in the photoelectric effect
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In the photoelectric effect there is a linear relation between kinetic energy of the released electrons \( W_{\text{kin}} \) and photon frequency \( f \). The Planck's constant \( h \) is the slope of the straight line.

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