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+// Scilab Code Ex4.2 : Page-91 (2010)
+D = 0.04;    // Diameter of circular aperture, cm
+f = 20;    // Focal length of convex lens, cm
+lambda = 6000e-008;    // Wavelength of light used, m
+// We have sin(theta) = 1.22*lambda/D = theta, for small theta, such that
+// For first dark ring
+theta = 1.22*lambda/D;    // The half angular width at central maximum, rad
+r1 = theta*f;    // The half width of central maximum for first dark ring, cm
+// We have sin(theta) = 5.136*lambda/(%pi*D) = theta, for small theta, such that
+// For second dark ring
+theta = 5.136*lambda/(%pi*D);    // The half angular width at central maximum, rad
+r2 = theta*f;    // The half width of central maximum for second dark ring, cm
+printf("\nThe radius of first dark ring = %4.2e cm", r1);
+printf("\nThe radius of second dark ring = %4.1e cm", r2);
+
+// Result 
+// The radius of first dark ring = 3.66e-002 cm
+// The radius of second dark ring = 4.90e-002 cm
+\ No newline at end of file