Momentum Question

[Megan Bundy 2K]

I wanted to clarify something that my UA brought up today: we should not use the wavelength = h / p equation on light, correct? My UA said that since photons have no mass, we cannot use that equation and we should use E=pc.

[sgarza]

Yes, the de broglie equation only applies to objects with mass and momentum, which would exclude photons because they have no mass.

[Holly Do 2J]

Hi,

So to explain the reasoning behind why we use E=hv for a photon and not the De Broglie's equation is because E=hv is used for things that do no have a particular mass. For example we would typically use it for light/photon, and these do not have measurable mass.

On the other hand you can use De Broglie's equation for elements like sodium because sodium does have an atomic mass. You can also use De Broglie for something like a baseball because that too has a mass.

[805757847]

Hi,

Yes, because that equation can only be used on particles that have a momentum, and because p = m*v, that particle has to have a mass. However, photons do not have a mass. This is interesting because this equation is derived from photon, but cannot be used on photon.

Hope this helps!

[905740390]

The de Broglie equation gives us the wavelength for an object with mass and momentum since the equstion is wavelength= planks constant/ mass x velocity.

[Mahika Saoji 3K]

Hi! You are right. We wouldn't use De Broglie's equation because it entails mass and momentum and photons do not have mass. You could use it for elements on the periodic table or even a ball because it has mass.

[haryn Shin 1H]

Yes, when we're dealing with photons, we just use the equation wavelength = c/v, and with mass, electrons, and momentum, we use the de broglie formula wavelength = h/p. Hope this helps!

[Xiang Li 2F]

Hi, I think you are right! The de broglie equation can only be applied to matters that have their own mass and momentum. Photons do not have those.

[Srikar_Chintala_1E]

Yup, that is correct. You only use De Broglie's equation when you are dealing with a particle that has mass, and photons don't exactly have much of a mass.

[305749341]

Yes, that is correct. DeBroglie's wavelength equation is to show that anything can technically have wave-like properties. The point was to show that electrons with mass 9.109x10^-31 kg or a baseball with some mass technically have wave-like properties and a corresponding wavelength value.