## Equations for quantum mechanics

Lauren Haight 1E
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Joined: Wed Sep 18, 2019 12:15 am
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### Equations for quantum mechanics

Hi, can someone please help me to distinguish when to use certain equations for the certain aspects of quantum mechanics? As in, which equations to use for energy, electrons and light, and when we cannot interchange these equations? Thank you.

Michelle N - 2C
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Joined: Wed Sep 18, 2019 12:19 am

### Re: Equations for quantum mechanics

Fiona Latifi 1A
Posts: 92
Joined: Sat Sep 14, 2019 12:16 am

### Re: Equations for quantum mechanics

The equations that we learned on Monday that pertain to light and electromagnetic radiation cannot be used for electrons. They were just used today to demonstrate how De Broglie derived his wavelength equation.

Hannah Lee 2F
Posts: 99
Joined: Thu Jul 11, 2019 12:15 am

### Re: Equations for quantum mechanics

c = λv or λ = c / v describes the inverse relationship between wavelength and frequency, with c = speed of light, and is used to describe electromagnetic radiation. You would use this equation when dealing with a photon of light or particles without mass.

E = hv describes the energy of a photon, with h = Planck's constant. Charged particles can emit or absorb EM radiation only in discrete "packets" of energy of this magnitude E = hv. This also applies to EM radiation/light.

λ = h / p, or λ = h / mv (De Broglie's Wave Equation), describes how any moving particle with momentum p has wave-like properties of wavelength λ. You would use this for dealing with any other particles with mass such as electrons, protons, etc. (You can't use this equation for massless particles like photons because you need mass to provide momentum (p = mv), and you would end up with 0 in the denominator.)

(Be careful to note that the "v"s in the equation are different - the "v" in c = λv describes frequency, while the "v" in λ = h / mv describes a particle's velocity.)