calculating wavelength
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 Posts: 39
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calculating wavelength
Since we know two equations involving wavelength, (c = (wavelength)(frequency) and wavelength = h/p) I was wondering when to use which equation. Does it just depend on the information given? Or are there certain times when you have to use the De Broglie wavelength versus the speed of light equation?

 Posts: 31
 Joined: Thu Sep 27, 2018 11:27 pm
Re: calculating wavelength
I think that it depends on the equation given. One equation requires frequency to solve for wavelength, while the other requires momentum (mass*velocity) to solve. I would choose the equation keeping these values in mind. Hope this helps!

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Re: calculating wavelength
De Broglie equation is h/mv where v (velocity) is not c so the de Broglie equation can be used when the speed of the particle is not at the speed of light whereas c=hv is mainly used for light calculations.

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 Joined: Thu Sep 27, 2018 11:18 pm
Re: calculating wavelength
You should use De Broglie to solve for the wavelength of a mass. Atoms and objects have mass but light does not. The p (momentum) of De Broglie can be split into (mass*velocity) and that is where mass can be seen. Between the two formula, it is best to just list all the given values and put question marks next to the ones you need to find/solve.

 Posts: 63
 Joined: Thu Sep 27, 2018 11:29 pm
Re: calculating wavelength
Dr. Lavelle mentioned that E = hv can only be used for light. However, De Broglie's equation of lambda=h/p can only be used for objects with "rest" mass and velocity. "Rest" mass basically means anything that has mass when stationary.

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 Joined: Thu Sep 27, 2018 11:16 pm
Re: calculating wavelength
Mukil_Pari_4H wrote:Dr. Lavelle mentioned that E = hv can only be used for light. However, De Broglie's equation of lambda=h/p can only be used for objects with "rest" mass and velocity. "Rest" mass basically means anything that has mass when stationary.
why is rest in quotes.. is there a significance? it is slightly confusing me..

 Posts: 30
 Joined: Thu Sep 27, 2018 11:17 pm
Re: calculating wavelength
How do we know when to combine De Broglie's equation with E = hv? Is it for specific conditions?

 Posts: 63
 Joined: Thu Sep 27, 2018 11:29 pm
Re: calculating wavelength
LeannaPhan14ALec1Dis1F wrote:Mukil_Pari_4H wrote:Dr. Lavelle mentioned that E = hv can only be used for light. However, De Broglie's equation of lambda=h/p can only be used for objects with "rest" mass and velocity. "Rest" mass basically means anything that has mass when stationary.
why is rest in quotes.. is there a significance? it is slightly confusing me..
There is no significance of the quotes.

 Posts: 35
 Joined: Thu Sep 27, 2018 11:15 pm
Re: calculating wavelength
The De Broglie equation can be used for any object that has rest mass, because it was found that just as light as both wave and particle properties, electrons also have both. So, the De Broglie equation is usually used to when the object's wavelength we are told to find has mass. If we are doing problems with massless particles like photons, then we use c=v*wavelength or E=hv.

 Posts: 39
 Joined: Thu Sep 27, 2018 11:24 pm
Re: calculating wavelength
Cade Okohira 1I wrote:The De Broglie equation can be used for any object that has rest mass, because it was found that just as light as both wave and particle properties, electrons also have both. So, the De Broglie equation is usually used to when the object's wavelength we are told to find has mass. If we are doing problems with massless particles like photons, then we use c=v*wavelength or E=hv.
Once we know wavelength of an object using De Broglie, how do we then use that wavelength to solve for other things? Can we plug that value into E=hc/lambda? Or are they supposed to be kept separate?
Re: calculating wavelength
The de broglie equation is used when taking mass into account. I.E. calculating the wave length of an electron or an atom instead of a photon of light.
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