Example33.22useaHeNelaser(wavelength633nm),andoorwidth(a)of1.5m)andashadowdistanceofL=2m.CommentonFigure33.1bexample 33.22:

EXAMPLE 33.2 Measuring wavelengths emitted by sodium atoms Light from a sodium lamp passes through a diffraction grating 36.08 fringe at 72.88 cm having 1000 slits per millimeter. The interference pattern is viewed 01 = tan 36.130 fringe at 73.00 cm on a screen 1:000 m behind the grating. Two bright yellow fringes are visible 72.88 cm and 73.00 cm from the central maximum. These angles must satisfy the interference condition dsine, = A, What are the wavelengths of these two fringes? so the wavelengths are A = dsin0,. What is d? If a 1 mm length of VISUALIZE This is the situation shown in Figure 33.9b. The two the grating has 1000 slits, then the spacing from one slit to the next fringes are very close together, so we expect the wavelengths to must be 1/1000 mm, or d = 1.000 X 10 m. Thus the wavelengths be only slightly different. No other yellow fringes are mentioned, creating the two bright fringes are so we will assume these two fringes are the first-order diffraction A = dsine = 589.0 nm fringe at 72.88 cm (m 589.6 nm fringe at 73.00 em SOLVE The distance y., of a bright fringe from the central maxi- mum is related to the diffraction angle by y., - Ltan0.,. Thus the ASSESS We had data accurate to four significant figures, and all diffraction angles of these two fringes are four were necessary to distinguish the two wavelengths