# Lightsorce through spectrometer

1. Mar 3, 2015

### SwedishFred

1. The problem statement, all variables and given/known data
A light hits a spektrometer perpendicular into a gitter with 300 slits/mm. You observes that a red and a blue line (in Visual light) coinciding. And the angle deflectionis 24.5°. What wavelenght have the red and the blue lines.
No n is given.

2. Relevant equations
d*sinα=n*λ

3. The attempt at a solution
First i calculated d
1/300000m = 3.33*10-6
((3.33*10-6)*(sin24.5))/625-9 2.5

((3.33*10-6)*(sin24.5))/500-9 2.5

so the red wavelenght is 625nm
so the blue wavelenght is 500nm
n=2.5

Is this correct ? can it be 2.5?? the blue is closer to n3 and red n2

2. Mar 3, 2015

### SammyS

Staff Emeritus
So, I take it that "gitter" is "grating".

I get approximately 2.2 and 2.7 as shown above in RED.

So, yes, use n = 2 for red & n = 3 for blue.

3. Mar 3, 2015

### TSny

Hello, SwedishFred.

You know that n must be an integer, so n cannot be 2.5. Think about this: Is it possible for two different wavelengths to overlap using the same value of n for each wavelength?

4. Mar 3, 2015

### SwedishFred

No that was what i was thinking about, so I understand it now, its much easier to see it happend ;-)
Thanx

5. Mar 3, 2015

### SammyS

Staff Emeritus
What do you get for the two wavelengths?

6. Mar 3, 2015

### SwedishFred

((3.33*10-6)*(sin24.5))/2
((3.33*10-6)*(sin24.5))/3
Red 690nm
Blue 461nm

True ?

Last edited: Mar 3, 2015