Lecture 47 – Lecture 48 Mirrors and Lenses Ozgur Unal NIS – PHYSICAL SCIENCE Lecture 47 – Lecture 48 Mirrors and Lenses Ozgur Unal

Mirrors A mirror is any surface that produces a regular reflection. Example: A pool of still water, a metal pan, shiny spoon etc. Mirrors can be flat, curved inward or curved outward. Plane mirrors: A flat, smooth mirror is a plane mirror. In a plane mirror, the image appears upright. If you stand 1 m from the mirror, your image appears 1 m behind the mirror, or 2 m from you.

Mirrors Virtual and real images: Your brain assumes that light rays travel in a straight line. Rays that enter your eyes seem to come from behind the mirror The image seems to be behind the mirror  virtual image Plane mirrors always form virtual images. If light rays from an object pass through the location of the image, the image is called a real image. Curved mirrors can form both real and virtual images.

Mirrors Concave mirrors: If the surface of a mirror is curved inward, it is called a concave mirror. The optical axis, or principal axis, is an imaginary line drawn perpendicular to the surface of the mirror at its center. Every light ray traveling parallel to the optical axis is reflected through a point on the optical axis called the focal point.

Mirrors Concave mirrors: The image formed by a concave mirror depends on the location of the object relative to the focal point. http://webphysics.davidson.edu/applets/Optics/prb1.html

Mirrors Convex mirrors: A mirror that curves outward like the back of a spoon is called a convex mirror. Light rays that hit a convex mirror diverge, or spread apart, after they are reflected. The reflected rays diverge and never meet, so a convex mirror forms only a virtual image. http://dev.physicslab.org/asp/applets/javaphysmath/java/dmirr/default.asp

Lenses A lens is a transparent object with at least one curved surface that causes light rays to refract. There are two types of lenses: convex and concave Convex lenses: A convex lens is thicker in the middle than the edges. Its optical axis pass through the thickest point and is perpendicular to the lens itself.

Convex Lenses When light rays approach a convex lens traveling parallel to its optical axis, the rays are refracted toward the center of the lens  Light rays traveling along the optical axis are not bent. Check out Figure 19!!

Concave Lenses A concave lens is thinner in the middle and thicker at the edges. Light rays that pass through a concave lens bend away from the optical axis. The rays spread out and never meet. The image is always virtual, upright and smaller than the object is.

The Human Eye The structure of the human eye:

The Human Eye Human eye can adjust to the varying brightness and intensity of light. Light intensity is the amount of light energy that strikes a certain area each second. Brightness is the human perception of light intensity.

Vision Problems Farsightedness: If you can see distant objects clearly but can’t bring nearby objects into focus, then you are farsighted. What type of lens should be used to correct this problem?

Vision Problems Nearsightedness: Nearsighted people can see close objects but cannot bring far objects into focus. What type of lens should be used to correct this problem?