## λ=h/p vs λ=hc/E

Noh_Jasmine_1J
Posts: 71
Joined: Fri Sep 28, 2018 12:15 am

### λ=h/p vs λ=hc/E

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 !

Becky Belisle 1A
Posts: 81
Joined: Fri Sep 28, 2018 12:18 am

### Re: λ=h/p vs λ=hc/E

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.

Kristen Kim 2K
Posts: 70
Joined: Fri Sep 28, 2018 12:16 am

### Re: λ=h/p vs λ=hc/E

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.

janeane Kim4G
Posts: 31
Joined: Fri Sep 28, 2018 12:28 am

### Re: λ=h/p vs λ=hc/E

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 !

Posts: 30
Joined: Fri Sep 28, 2018 12:24 am

### Re: λ=h/p vs λ=hc/E

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.

Nawaphan Watanasirisuk 3B
Posts: 58
Joined: Tue Nov 28, 2017 3:03 am

### Re: λ=h/p vs λ=hc/E

It also depends on what values you are given/asked

105002507
Posts: 30
Joined: Fri Sep 28, 2018 12:15 am

### Re: λ=h/p vs λ=hc/E

what units do we use for each of the constants/ variables?