How can the wavelength of blue light be 750nm?

1. Jun 11, 2014

FaroukYasser

1. The problem statement, all variables and given/known data
A Visible light is shone on a diffraction grating. Two rays are produced, One Orange ray with 600 nm which is at the fifth order maxima. It coincides with a blue ray at the fourth order maxima. Find the wavelength of the blue light.

2. Relevant equations
n x lamda = dsin(theta)
where n = number of order
lamda = wavelength

3. The attempt at a solution
Basically what I did was say that (d) was constant since it was the same diffraction grating. and the same Sin(theta) since they occurred and coincides at the same point so dsin(theta) is the same for both, Then I did:
For orange light:
5 x 600 x 10^-9 = dsin(theta) (1)*
For blue light:
4 x Wavelength of blue light = (1)*
4 x lamda = 5 x 600 x 10^-9
lamda = 750 nano meters!!!
How can the wavelength of blue light be 750 nm!!! This is the wavelength of red light!!
Is there a mistake in the question?
Thanks.

2. Jun 11, 2014

ehild

Certainly, they did. Perhaps mixed 4 and 5.

ehild

3. Jun 11, 2014

FaroukYasser

Thanks. That's a relief. Spent almost an hour trying to figure out if there was any other possible way to solve it. Thanks alot