3. A sheet of acrylic can be a molded into a Fresnel lens to provide a reading aid. Consider an arrangement that provides a x2 magnification for the reader when

placed 100 mm above the text (take d =550 nm corresponding to the middle of the visible spectrum). What is the diameter of the central Fresnel zone? How many Fresnel zones are there across the diagonal of an A4 (210 mm×297 mm) format magnifier? Hint: think about what focal length for the lens is required.