Difference between E=hv and E=hc/v?


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Xinying Wang_3C
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Difference between E=hv and E=hc/v?

Postby Xinying Wang_3C » Mon Oct 19, 2020 4:44 am

Hi,
I was working on the Sapling homework, and I got confused between the formula E=hv and E=hc/v. I am wondering what is the difference between these two formulas and when to use which?

Thanks in advance!

Truman Chong Dis 3G
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Re: Difference between E=hv and E=hc/v?

Postby Truman Chong Dis 3G » Mon Oct 19, 2020 7:03 am

I think you may have mistaken E= hc/λ for E=hc/v. E=hc/λ is the same as E=hv where v is substituted using the equation c=λν solved for v. E=hv and
c=λν can be used in conjunction with each other to find E, λ, or ν. Additionally, substituting one equation into another helps to solve when we only have the value of one of the variables which may not inherently show up in one of the equations.

OwenSumter_2F
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Re: Difference between E=hv and E=hc/v?

Postby OwenSumter_2F » Mon Oct 19, 2020 9:25 am

To add on to what Truman said, they are the same formula, one is just shorter (E=hv). The other, E=hc/λ is the combination of E=hv and c=λv, it is just there to show how the two equations work together.

Alexa Pham 1D
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Re: Difference between E=hv and E=hc/v?

Postby Alexa Pham 1D » Mon Oct 19, 2020 10:01 am

I think you mean E=hc/λ , not E=hc/v, so I will explain the difference between E=hv and E=hc/λ . Both equations find the same thing, which is the energy. However, depending on what information is given in the problem, you'd use one over the other. For example, if they asked to find the energy of a photon and they give you the frequency, you'd use E=hv. However, if they gave you wavelength, you use E=hc/λ , since c/λ is the equation to find frequency.

anikamenon2H
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Re: Difference between E=hv and E=hc/v?

Postby anikamenon2H » Mon Oct 19, 2020 10:53 am

They are the same equation really, just in the second one the frequency is being substituted by a different formula ( v = c / λ). You use the second/longer version when you need to find the wavelength usually because then you have a variable present in the equation. The longer way to do it would be to find the frequency using E = hv and then plug in that frequency value into c = λ * v to find the frequency. E= (hc)/λ is just meant to make the calculation go faster.

Hope this helps!

Samantha Lee 1A
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Re: Difference between E=hv and E=hc/v?

Postby Samantha Lee 1A » Mon Oct 19, 2020 11:26 am

E = hv and E = hc/lambda will give you the same energy. There are used when you aren't given enough information to use the other equation. For example, if you are given h, c, and the wavelength (no frequency, v), then use E = hc/lambda. If you are given frequency, but not wavelength, use E = hv. Hope that helps

Alexandra Salata 2L
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Re: Difference between E=hv and E=hc/v?

Postby Alexandra Salata 2L » Tue Oct 20, 2020 7:02 am

E=h/v is the relationship showing the energy per photon, where the h represents Planck's constant (6.626x10^-34) and v represents the frequency.
The equation E= hc/v does not exist, but I think you're referring to E= hc/ λ, which is the relationship between Planck's constant, the constant speed of light, and the wavelength of this light that you are using in the question.

Navdha Sharma 3J
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Re: Difference between E=hv and E=hc/v?

Postby Navdha Sharma 3J » Tue Oct 20, 2020 10:46 pm

I think you meant to ask the difference between E = hv and E= hc/λ. They are essentially the same thing.

We know, c = λv
=> v = c/λ --- equation 1

So, E = hv
=> E = hc/λ (from equation 1)

Hope it helps!

Elizabeth Kaplan 3I
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Re: Difference between E=hv and E=hc/v?

Postby Elizabeth Kaplan 3I » Wed Oct 21, 2020 7:42 am

Hi! Those are equations (I'm assuming you meant E=hc/lambda) are equivalent! The first one, E=hv, is used to calculate Energy when the frequency is known/given, while the second one, E=hc/lambda, is used to calculate Energy when the wavelength is known/given. E=hc/lambda is merely the combination of E=hv and v=c/lambda.

aashmi_agrawal_3d
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Re: Difference between E=hv and E=hc/v?

Postby aashmi_agrawal_3d » Wed Oct 21, 2020 8:48 am

I think you mean E=hc/λ and that is basically a combination of E=hv and C=λv. This is because v can also be represented as c/λ.


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