I got you.
The glancing angle for the second order diffraction of X-rays with a wavelength of 0.071 nm diffracted by the (110) plane of rock salt with a lattice constant of 0.28 nm can be calculated using Bragg's law:
2d sinθ = nλ
where d is the interplanar spacing of the (110) plane, n is the order of the diffraction, λ is the wavelength of the X-rays, and θ is the glancing angle.
For the second order diffraction (n = 2), we have:
2d sinθ = 2λ
The interplanar spacing of the (110) plane can be calculated using the formula:
d = a/√(h^2 + k^2 + l^2)
where a is the lattice constant, and h, k, and l are the Miller indices of the (110) plane. For rock salt, h = 1, k = 1, and l = 0 for the (110) plane.
Substituting the values given in the problem, we get:
d = 0.28 nm / √(1^2 + 1^2 + 0^2) = 0.14 nm
Substituting the values for d, n, and λ, we get:
2(0.14 nm) sinθ = 2(0.071 nm)
Simplifying, we get:
sinθ = 0.51
Taking the inverse sine, we get:
θ = 30.2 degrees
Therefore, the glancing angle for the second order diffraction is approximately 30.2 degrees.