Textbook,
Chapter 5, Page 158: P2, P6, PM1
P2. Accommodation is the process that the eye
uses to focus on objects at different distances. It is achieved by changing the
focal length of the eye-lens. The eye-lens is normally focused on a very
distant object when the muscles are relaxed. As an object moves closer to the
eye, the muscles that do this increase the strength of the eye-lens and
therefore shorten its focal length until the object is in focus on the retina.
P6. Black light contains ultra-violet light in
addition to some visible light in the blue and purple regions of the spectrum.
The light appears fuzzy because of chromatic aberration in the eye. The
eye-lens cannot focus simultaneously on the blue and ultra-violet portions of
the spectrum because the index of refraction of the eye-lens changes with
wavelength (This is called chromatic aberration).
PM1.
The speed of a lens is the ratio of the focal length to the diameter. Using the
values in the problem, the focal length is given as 16 mm and the diameter is
given as 4 mm. Therefore the speed is 16/4 = f/4.