# Light scattering homework question (rayleign scattering)

1. Sep 9, 2013

### haitianstudent

1. The problem statement, all variables and given/known data
Infrared telescopes, which use special infrared detectors, are able to peer farther into star-forming regions of the galaxy because infrared light is not scattered as strongly as is visible light by the tenuous clouds of hydrogen gas from which new stars are created.

2. Relevant equations

For what wavelength of light is the scattering only 2.00% that of light with a visible wavelength of 490nm ?

3. The attempt at a solution
the formula is I(490)/IR=(lamda/490nm)^4.
I'm really not sure what I am doing wrong here

2. Sep 9, 2013

### Bryson

Did you solve for lamda? What did you do?

3. Sep 9, 2013

### haitianstudent

I first took lamda and 490 to the 4th power and I got (lamda)^4/5.77*10^10. Then I crossed multiply by 200, I then recived 1.15E13...and I took the fourth root of that and received 1841 but its apparently wrong

4. Sep 10, 2013

### Staff: Mentor

2% is not = 1 / 200

The formula is correct. Equate it to 0.02 and solve for the sole unknown, viz., λ

Are you told the correct answer?

5. Sep 10, 2013

### Bryson

Note infrared is 700nm to 1mm.