## When to use de Broglie and what numbers to use

$\lambda=\frac{h}{p}$

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### When to use de Broglie and what numbers to use

In sapling, there are some problems where they give you the equation 3.29 x 10^15(1/n1^2 - 1/n2^2) and another identical one except they use 1.0974 as rydberg's constant. How would you know which one to use and what are the differences in both of these?

Savana Maxfield 3F
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### Re: When to use de Broglie and what numbers to use

I have been wondering the same thing. I think maybe the values are in different units or used in different circumstances? If someone knows more about this, I would love some additional information!

Yuehan_Wu_3K
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### Re: When to use de Broglie and what numbers to use

The trick I used is not to remember the situation applied to the equations, instead, paying attention to the symbols in the equations. If the symbols in the equations are not used, then not using the equations.

Ivan Chen 2H
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### Re: When to use de Broglie and what numbers to use

They are two constants to find different things. 3.29 x 10^15 is used in Hz in order to find the frequency of a given line, while 1.0974*10^-7 m^-1 is used to find 1/wavelength

Joseph Hsing 2C
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### Re: When to use de Broglie and what numbers to use

Rydberg formula is used to calculate the wavelength of spectral lines, while de Broglie describes the wavelength of any particle. There are 3 different numbers I believe when using Rydberg and the last one not mentioned was 2.178 x 10^-18 J for energy calculations. Look for what the question calls for: frequency, energy, or wavelength and use the corresponding constant.

605291562
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### Re: When to use de Broglie and what numbers to use

I've noticed the same thing, I've always just used the equation on our equation sheet and process done in class because that's how we should do it on the exams, but you get the right answer either way so I don't think it really matters which process you use.

claire ikemiya_2I
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### Re: When to use de Broglie and what numbers to use

They did that instead of using the Rydberg's equation on our formula sheet because they combined 2 equations. Normally you would do
lamda = c/v and then plug into Rydbergs equation, but they combined it and so the 1.0974 x 10^-7 is R constant divided by speed of light.

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### Re: When to use de Broglie and what numbers to use

Your best bet, in my opinion, is to avoid the constant given by the Sapling people and instead use the one that Dr. Lavelle provided while using the equation that he used in his lecture. This is because using the other equation demands that you think about whether absorption or emission is happening and you have to figure out which is n1 and which is n2. If you use Dr. Lavelle's equation, you only have to remember that initial energy is subtracted from final energy.

Eve Gross-Sable 1B
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### Re: When to use de Broglie and what numbers to use

Is there a definite answer for when to use de Broglie and when not to? I thought that it was straightforward but then it seemed like it was being applied to whatever they wanted it to be applied to in the sapling problems. Like you are able to calculate using de broglie for electrons but then also not using de broglie which doesn't;t make sense to me.