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### Wavelength= (h/p)

Posted: Sun Apr 22, 2018 11:35 pm
Hello. In lecture, professor Lavelle said the equation Wavelength= (h/p) applies to everything but light. I was wondering why? Is it because light doesn't have mass? And if so, do photons not have mass?

### Re: Wavelength= (h/p)

Posted: Sun Apr 22, 2018 11:39 pm
You are correct. λ=h/p cannot apply to light because light does not have mass. As a consequence, photons also have no mass.

### Re: Wavelength= (h/p)

Posted: Sun Apr 22, 2018 11:44 pm
Hi, I'm not 100% sure but, photons do not have mass per se. De Broglie's is not the appropriate equation to used for photons at rest, however if they have a "non zero" momentum, then I think we do use his equation. Again, don't quote me. I tried :)

### Re: Wavelength= (h/p)

Posted: Sun Apr 22, 2018 11:56 pm
the reason why that formula doesn't apply to light is because it doesn't contain mass. hope this answers your question :)

### Re: Wavelength= (h/p)

Posted: Sun Apr 22, 2018 11:59 pm
Thank you this is helpful., also i think the mass of an electron is 9.10938356 × 10-31 kilograms

### Re: Wavelength= (h/p)

Posted: Mon Apr 23, 2018 3:30 pm
This equation applies to the DeBroglie wavelength which applies to calculating the wavelength of a particle as a means to look at its wave-like properties. It mainly applies to subatomic particles because those particles are the only ones that yield a measurable value for the wavelength.

### Re: Wavelength= (h/p)

Posted: Mon Apr 23, 2018 8:16 pm
I believe you're correct it's because photons do not have a mass.

### Re: Wavelength= (h/p)  [ENDORSED]

Posted: Sat Apr 28, 2018 3:04 pm
Just to clarify the De Broglie equation does not work for objects without a rest mass (such as light). If you think about how light always has a constant speed it will never stop and thus never have a resting mass.