## Question about Problem done in Discussion

alex_4l
Posts: 82
Joined: Thu Sep 26, 2019 12:18 am

### Question about Problem done in Discussion

In discussion 4C this past week, we did an equation and I was a little confused with one of the steps
the question was "green color appears when visible light has a wavelength of 780nm, what will E=,V= and V-=?"

for this problem we used E=hc/sigma to get 6.626x10^-34JS x 3x10^8m.s^-1/ 780x10^-9m so E=2.55x10^-19J
next, we used v=c/sigma to get 3x10^8m.s^-1/780x10^-9m so v=3.85x10^14s^-1
lastly we used v=cv- to get 10=3x10^8m.s^1 x v- and we divided 3x10^8m.s^-1 to get v- alone which resulted in v- = 3.33x10^-8s

I understand the entirety of the problem with finding each value, but I'm a bit confused with the last equation of v=cv- why 10 was used to represent v, wouldn't we just use the value we got for v in the previous equation and plugged that in for the last part of the problem?

Chem_Mod
Posts: 18158
Joined: Thu Aug 04, 2011 1:53 pm
Has upvoted: 426 times

### Re: Question about Problem done in Discussion

Dear Student,
In that question we were learning how to convert other parameters like Energy, Frequency, and wave number if one of the parameter like wavelength is given. Let say we have wavelength value equals to 500 nm. To get energy we will use equation E=hc/wavelength. h is planks constant and c is speed of light. Similarly, if we wanna know frequency we can get from , frequency = c/wavelength, if we wanna get wavenumber, wavenumber = 1/ wavelength.
If you have any other question feel free to ask me in discussion. Good Luck

alex_4l
Posts: 82
Joined: Thu Sep 26, 2019 12:18 am

### Re: Question about Problem done in Discussion

I understand the equations and when to use them, I just don't understand why 10 was chosen as the value for V in the last equation and why it wasn't the number we had gotten for it in the earlier equation.