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

$c=\lambda v$

Xinying Wang_3C
Posts: 94
Joined: Wed Sep 30, 2020 9:39 pm

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

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?

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

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?

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
Posts: 69
Joined: Wed Sep 30, 2020 10:03 pm

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

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?

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?

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
Posts: 91
Joined: Wed Sep 30, 2020 9:39 pm

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

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
Posts: 96
Joined: Wed Sep 30, 2020 9:46 pm

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

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
Posts: 113
Joined: Wed Sep 30, 2020 9:32 pm

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

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
Posts: 105
Joined: Wed Sep 30, 2020 9:39 pm

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

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.