# Bragg Law and Effect of Doubling Wavelength

1. Apr 9, 2013

### elemis

My lecturer discussed bragg's law a few weeks ago and described how the angle theta changes as the wavelength is doubled.

I cant seem to duplicate his result.

I know that the bragg condition for a maxima would reduce to : dsinθ=mλ when the wavelength is doubled.

In his example he knew that maxima were observed at 20.5 and 44.5 degrees but he gave no other values.

How would I go about predicting the angles at which the maximas are now observed ?

2. Apr 9, 2013

### Staff: Mentor

If you double λ and m and d stay constant, sinθ doubles as well. You can calculate sinθ in your example.

3. Apr 9, 2013

### elemis

True, so sin(20.5) = 0.3502... This multiplied by 2 gives : 0.700.... Sin inverse of this gives 44.5 degrees.

But if I double sin(44.5) I get a value larger than 1. How is it possible to take the sine inverse of this ?

EDIT : Does this imply there is only one maxima now at 44.5 degrees ?

4. Apr 10, 2013

### Staff: Mentor

The 44.5-maximum has no equivalent for the doubled wavelength, right.