Reflection grating consists of an array of equally spaced, identical
narrow reflecting grooves or ridges on a non-reflecting surface. The spacing
between
the grooves is m. Light from a distant source falls normally
(that is, perpendicularly to the surface) on the grating. A distant observer
observes light reflected at angle , see Fig. 2.
(a)
If the source emits blue light (wavelength
nm),
what values of the angle correspond to
principal maxima? Does the answer depend on ?
(b)
If the source emits red light (wavelength
nm),
what values of correspond to principal maxima?
(c)
Using the above results, explain why the surface of a
compact disc looks ``rainbow-colored'' when seen from an angle.
HINT: Natural light is a mixture of waves with wavelength spanning the
whole spectrum from blue to red.