21.2. The Double-Slit Experiment http://www.ck12.org
tan 8. 7 ◦=Z
L
=
3. 025 × 10 −^1 m
L→
L=
3. 025 × 10 −^1 m
tan 8. 7 ◦= 1. 98 m→
L= 2. 0 mDiffraction from a single slit
Recall that when a wave passes through an opening, such as in this case of a light wave passing through a slit,
diffraction occurs. If we restrict our attention to only one slit, we can see that different parts of the diffracted wave
will be subject to constructive and destructive interference, just as we observed with two slits.Figure21.9 shows
the path of light rays diffracting through one slit. In other words, when we observe the interference pattern for a
double-slit, there is yet another interference pattern present due to each slit. More advanced texts will have more to
say on this topic. If you would like to learn about this, see the link below.
FIGURE 21.9
http://demonstrations.wolfram.com/SingleSlitDiffraction/
Diffraction gratings
Diffraction gratings are composed of many equally spaced slits instead of two slits. They produce much sharper and
better separated maxima and minima, and therefore are very useful in determining the wavelength of a particular
color. Diffraction gratings are an important component in astronomicalspectroscopeswhich are designed for the
purpose of wavelength determination, seeFigure24.6.
When heated and observed through a spectroscope, each chemical element has a unique line spectrum (a specific set
of colors in specific locations), as shown inFigure24.6.
Light from the sun, as seen through a spectroscope, shows that the sun has many of the same elements present on the
Earth. (We will discuss this in greater detail later.) A spectroscope, therefore, enables us to determine the chemical
composition of the sun, stars, and planets.
Diffraction gratings are typically of two kinds: transmission gratings, where the light passes through the grating, and
reflection gratings, where fine lines are etched into a metallic substance which reflects the interference pattern.
The equation describing the interference pattern is the same as for the double slit grating.