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### λ=h/p vs λ=hc/E

Posted: Tue Oct 23, 2018 2:42 pm
Hi, I am confused on when to use the equation λ=h/p vs λ=hc/E or if they are interchangeable. thank you so much !

### Re: λ=h/p vs λ=hc/E

Posted: Tue Oct 23, 2018 2:47 pm
λ=hc/E is the same as λ=h/p except because c is used it is specific to light. λ=h/p cannot be used for light because p=mv and photons are massless.

### Re: λ=h/p vs λ=hc/E

Posted: Tue Oct 23, 2018 2:48 pm
λ=h/p is the de Broglie wavelength equation. This is used to find the wavelength that is emitted by any moving particle since everything technically has wavelike properties, whether they are detectable or not.
λ=hc/E is the equation to find quantum energy of a photon, from the photoelectric effect. It is basically combining the speed of light formula and the E=hv formula, as frequency in the speed of light formula is plugged into E=hv, and then rearranged so the formula focuses on finding wavelength.

### Re: λ=h/p vs λ=hc/E

Posted: Tue Oct 23, 2018 2:51 pm
Hello! This first equation λ=h/p is the debroglie wave equation, it finds the hypothetical wavelengths of all items with a velocity and mass. λ= hc/E is the photon wavelength equation, used when measuring the energy of photons- note there is variable c, the speed of light, where λ=h/p does not. I don’t believe they are interchangeable as the values that they require are quite different. Hope this helped !

### Re: λ=h/p vs λ=hc/E

Posted: Wed Oct 24, 2018 10:02 pm
As the previous replies said, λ=h/p debroglie wave equation when the momentum or (m*v) is given. λ=hc/E is used when Energy (J) is given.

### Re: λ=h/p vs λ=hc/E

Posted: Thu Oct 25, 2018 2:19 am
It also depends on what values you are given/asked

### Re: λ=h/p vs λ=hc/E

Posted: Thu Oct 25, 2018 7:37 pm
what units do we use for each of the constants/ variables?