8.4.2—The use of a diffraction grating to determine the wavelength of light

Use a grating of known line spacing, observe a bright maximum of order n, measure θ and calculate λ=d sinθ/n.

Measure symmetric +n and −n angles where possible, average them, and convert line density to metres per line before substituting.

A laser’s first-order angle on a calibrated grating gives its wavelength; repeating for another colour compares wavelengths directly.

Do not use the angle from the grating normal incorrectly, and do not confuse line density with slit spacing.