Sapling Week 2/3 HW Question 6

$c=\lambda v$

Ven Chavez 2K
Posts: 56
Joined: Mon Feb 24, 2020 12:16 am

Sapling Week 2/3 HW Question 6

Hi, the solution for n2 for question 6 says to use the Rydberg Equation but in class, Dr. Lavelle was going over another way to solve it. I tried doing it the way Dr. Lavelle showed but am ending up confused. Can someone explain the steps to find the same answer as found using the Rydberg Equation? A violet line is observed at 434.0 nm in the spectrum of atomic hydrogen. Determine the values of n for the beginning and ending energy levels.

Aliya 1H
Posts: 68
Joined: Wed Sep 30, 2020 9:34 pm

Re: Sapling Week 2/3 HW Question 6

Hi! I had my discussion today and we went over this type of problem. She said to look at what the wavelength is (434 nm) and then look at what series that would be in. In this case, it would be in the Balmer series and the ending energy level is always going to be n=2 for this series. I am not sure if that's the way Dr. Lavelle wants us to figure that out but she told us to do that and it works. Then, she gave us the equation $\frac{1}{\lambda }= R_{h}\left [\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right]$
and said that the Rydberg constant $R_{h}$ = $1.097x10^{7}m^{-1}$.
So, you want to plug in the wavelength in meters as $\lambda$ in that equation, plug in the n=2 and solve for the other n:
$\frac{1}{4.34x10^{-7}m}= (1.097x10^{7}m^{-1})\left [ \frac{1}{4} -\frac{1}{n_{2}^{2}}\right ]$

nayha a 1E
Posts: 57
Joined: Wed Sep 30, 2020 9:54 pm

Re: Sapling Week 2/3 HW Question 6

Hi! I solved this problem in a similar way. I used the equation v=c/λ to get my frequency. Then, I used the Rydberg Formula v= R(1/n1^2 - 1/n2^2) where R is Rydberg's constant 3.29x10^15. Then, I plugged in the values I had and 2 for n1 (due to the value being within the Balmer Series, as someone else explained). After that I solved for n2.

AndrewNguyen_2H
Posts: 55
Joined: Wed Sep 30, 2020 9:59 pm

Re: Sapling Week 2/3 HW Question 6

Aliya 2J wrote:Hi! I had my discussion today and we went over this type of problem. She said to look at what the wavelength is (434 nm) and then look at what series that would be in. In this case, it would be in the Balmer series and the ending energy level is always going to be n=2 for this series. I am not sure if that's the way Dr. Lavelle wants us to figure that out but she told us to do that and it works. Then, she gave us the equation $\frac{1}{\lambda }= R_{h}\left [\frac{1}{n_{1}^{2}}-\frac{1}{n_{2}^{2}}\right]$
and said that the Rydberg constant $R_{h}$ = $1.097x10^{7}m^{-1}$.
So, you want to plug in the wavelength in meters as $\lambda$ in that equation, plug in the n=2 and solve for the other n:
$\frac{1}{4.34x10^{-7}m}= (1.097x10^{7}m^{-1})\left [ \frac{1}{4} -\frac{1}{n_{2}^{2}}\right ]$

If it's Balmer and the ending energy level is n=2 shouldn't the other n2 be equal to 2? n2 Is the final energy level right?

Sophia Stewart 3F
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Joined: Wed Sep 30, 2020 9:48 pm

Re: Sapling Week 2/3 HW Question 6

I get how this would be solved using Rydberg, but I, like Ven, was also having issues solving it the way Lavelle taught us. Was anyone able to get the correct answer that way? My roommate tried the problem too and got the same wrong answer as I did.

Antonio Garcia 3A
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Joined: Wed Sep 30, 2020 10:08 pm

Re: Sapling Week 2/3 HW Question 6

Does Lavelles way he showed in lecture get the same answer? I keep on getting it wrong using Lavelles way I'm wondering if its a mistake I am making or if it doesn't apply to this problem.

Sophia Stewart 3F
Posts: 60
Joined: Wed Sep 30, 2020 9:48 pm

Re: Sapling Week 2/3 HW Question 6

@Antonio, I think the problem I was having, and probably you were also having, was making sure that when you plugged the energies (-hR/n^2) into the change in energy equation (final energy minus initial energy), you change the double negative into a positive. To illustrate, -hR/n^2 minus -hR/n^2 would become -hR/n^2 minus -hR/n^2 .

Melanie Lin 3E
Posts: 55
Joined: Wed Sep 30, 2020 9:38 pm

Re: Sapling Week 2/3 HW Question 6

Hi all! I got super stuck on this problem for a while too! Turns out my biggest problem was mixing up my constants so maybe try making sure you have the correct units being cancelled out and having the correct numbers? Idk but aside from what Sophia said those two were what got me wrong answers.