Confused about equations


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Lizette Noriega 1H
Posts: 105
Joined: Wed Sep 18, 2019 12:15 am

Confused about equations

Postby Lizette Noriega 1H » Thu Oct 31, 2019 11:24 am

Hello,

This is a dumb question but I need clarification as to when you use certain equations since I always seem to mix them up. For instance, what kinds of problems indicate the use of the de Broglie equation (λ = h/mv) in contrast to the equations for wavelength (c= λv) and energy (E=hv)?

Thanks!

Daniel Toscano 1L
Posts: 95
Joined: Tue Nov 13, 2018 12:18 am

Re: Confused aout equations

Postby Daniel Toscano 1L » Thu Oct 31, 2019 11:38 am

c= λv and E=hv apply to light (photons). I think De Broglie's (λ=h/(mv)) applies to particles (electrons), as do Heisenberg's and Schrodinger's equations.

Michael Du 1E
Posts: 117
Joined: Sun Sep 22, 2019 12:16 am

Re: Confused about equations

Postby Michael Du 1E » Thu Oct 31, 2019 7:58 pm

Adding to Daniel, you would use the De broglie equation when the velocity of some particle or so is given. The other equations have no correlation with velocity in it and you would think about using them when trying to solve for frequency or so.

WesleyWu_1C
Posts: 117
Joined: Thu Jul 25, 2019 12:16 am

Re: Confused about equations

Postby WesleyWu_1C » Thu Oct 31, 2019 11:38 pm

The reason why you can only use c = λv for light is because pretty much everything else you need to find the wavelength for, has mass. For example, an electron has mass and mass is not considered in the c = λv. That's why if you want to find the wavelength (λ) for an electron you use the equation λ = h/p.

Minh Ngo 4G
Posts: 137
Joined: Thu Jul 25, 2019 12:17 am

Re: Confused about equations

Postby Minh Ngo 4G » Fri Nov 01, 2019 12:17 am

Use deBrogile when you are given a mass

Petrina Kan 2I
Posts: 102
Joined: Fri Aug 30, 2019 12:17 am

Re: Confused about equations

Postby Petrina Kan 2I » Sun Nov 03, 2019 2:28 am

According to the review session I went to, you would use c = λv only for light since it incorporates the speed of light. You would then use the DeBroglie equation for anything else, as these items will most likely be given with a mass in the problem. You can incorporate that with the E=hv equation because that one is not specific to light. Just make sure you don't use DeBroglie for light!

Caitlin Ciardelli 3E
Posts: 44
Joined: Wed Sep 18, 2019 12:19 am

Re: Confused about equations

Postby Caitlin Ciardelli 3E » Sun Nov 03, 2019 6:09 pm

only use c= λv when there is light involved!!!!
Whenever there is a mass mentioned or involved in the problem DO NOT USE THE LIGHT EQUATIONS!!! Instead use λ=h/(mv)

Whether or not mass is involved will determine which equation you will use

AronCainBayot2K
Posts: 101
Joined: Fri Aug 30, 2019 12:17 am

Re: Confused about equations

Postby AronCainBayot2K » Sun Nov 03, 2019 6:35 pm

When mass is given, use De Broglie hence the "m" in the equation and not on the other light equations. Also the light equations given, usually relate to photons where as De Broglie relates to electrons.


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