Exploring the Balmer Series: Counting Spectral Lines with Increasing Wavelengths

[stickplot]

Homework Statement

In the Balmer series, how many spectral lines have the wavelength greater than 400 nm?

Homework Equations

1/lambda= R(1/2^2-1/n^2)
lambda=wavelength
r=rhydberg constant 1.097x10^7
n= 3,4,5...
balmer series is visible light

The Attempt at a Solution

ok so i know the balmer series starts with 400 nanometers because its visible light, but i don't understand how to see how many spectral lines have wavelength greater.

 

[Delphi51]

You could just look up the Balmer Series in a book or on the web and count them.
Or use the formula to calculate the wavelengths - put in n=3, calculate. Put in n=4, calculate. Pretty soon you will have all the wavelengths you need!

 

[stickplot]

ok. but when i do the calculating up to what number do i go? because i thought it went from 2 on.

 

[Delphi51]

Yes, it does go on forever - 2 to infinity. But after calculating 2 or 3 wavelengths, you will see that you don't have to do very many of them the answer your question.

 

[stickplot]

o ok i got it. wavelength decreases when you increase n
thanks appreciate your response