calculating wavelength

$c=\lambda v$

Kirsty Star 2H
Posts: 48
Joined: Fri Sep 28, 2018 12:24 am

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?

gillianozawa4I
Posts: 31
Joined: Fri Sep 28, 2018 12:27 am

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!

Jeffrey Xiao 4A
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Joined: Fri Sep 28, 2018 12:28 am
Been upvoted: 1 time

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.

Vicky Lu 1L
Posts: 60
Joined: Fri Sep 28, 2018 12:18 am

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.

Mukil_Pari_2I
Posts: 87
Joined: Fri Sep 28, 2018 12:29 am

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.

LeannaPhan14BDis1D
Posts: 57
Joined: Fri Sep 28, 2018 12:16 am

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..

RoopshaChatterjee 1G
Posts: 30
Joined: Fri Sep 28, 2018 12:17 am

Re: calculating wavelength

How do we know when to combine De Broglie's equation with E = hv? Is it for specific conditions?

Mukil_Pari_2I
Posts: 87
Joined: Fri Sep 28, 2018 12:29 am

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: 47
Joined: Fri Sep 28, 2018 12:15 am

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.

Kirsty Star 2H
Posts: 48
Joined: Fri Sep 28, 2018 12:24 am

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?

905096106
Posts: 30
Joined: Fri Oct 05, 2018 12:17 am

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.