Identify the wavefront and ray pattern in each case: (a) sunlight entering a lab window, (b) light 1 cm from a tiny LED point source, (c) light from a long fluorescent tube, (d) a parallel laser beam focused by a convex lens of f = 10 cm — describe the wavefront just after the lens and 10 cm beyond it. Step 1: (a) The Sun is effectively at infinity → plane wavefronts, parallel rays (a parallel beam). Step 2: (b) 1 cm from a point source → spherical wavefronts: tiny expanding spheres, rays radial outward. Step 3: (c) Fluorescent tube → cylindrical wavefronts: expanding cylinders coaxial with the tube, rays radial in planes perpendicular to the tube. Step 4: (d) Just after the lens the plane wavefront becomes a converging spherical wavefront (a shrinking spherical cap); 10 cm beyond, at F, it collapses to a point (the focus) — then re-expands as a diverging spherical wavefront. The lens's whole job is this plane→spherical wavefront conversion.