# PHYS 2212 Module 14

14: Geometric Optics and Image Formation

Cloud Gate is a public sculpture by Anish Kapoor located in Millennium Park in Chicago. Its stainless steel plates reflect and distort images around it, including the Chicago skyline. Dedicated in 2006, it has become a popular tourist attraction, illustrating how art can use the principles of physical optics to startle and entertain. (credit: modification of work by Dhilung Kirat)

This module introduces the major ideas of geometric optics, which describe the formation of images due to reflection and refraction. It is called “geometric” optics because the images can be characterized using geometric constructions, such as ray diagrams. We have seen that visible light is an electromagnetic wave; however, its wave nature becomes evident only when light interacts with objects with dimensions comparable to the wavelength (about 500 nm for visible light). Therefore, the laws of geometric optics only apply to light interacting with objects much larger than the wavelength of the light.

In this module, we will discuss how the light gets from a source to your eye, so you can see the object. If you look at the Sun (which you shouldn’t do, so please don’t) the light travels directly into your eye, so you can see it. But you could use a tool to observe it instead. You could use a mirror so that the light from the Sun reflects from the mirror and then into your eye. Or you could hold a piece of glass or clear plastic between the Sun and your eye. In this case the light would bend when it travels into the glass and out again, but you would still be able to see the Sun once the light rays reached your eye. It just might look a little deformed depending on the shape of the glass. This is what we will discuss in this Module – using mirrors and lenses to see images of objects.

#### 14.1 Images Formed by Plane Mirrors

• Describe how an image is formed by a plane mirror.
• Distinguish between real and virtual images.
• Find the location and characterize the orientation of an image created by a plane mirror.

#### 14.2 Spherical Mirrors

• Describe image formation by spherical mirrors.
• Use ray diagrams and the mirror equation to calculate the properties of an image in a spherical mirror.

#### 14.3 Images Formed by Refraction

• Describe image formation by a single refracting surface
• Determine the location of an image and calculate its properties by using a ray diagram
• Determine the location of an image and calculate its properties by using the equation for a single refracting surface

#### 14.4 Thin Lenses

• Use ray diagrams to locate and describe the image formed by a lens
• Employ the thin-lens equation to describe and locate the image formed by a lens

#### 14.5 The Eye

• Understand the basic physics of how images are formed by the human eye
• Recognize several conditions of impaired vision as well as the optics principles for treating these conditions

#### 14.6 The Camera

• Describe the optics of a camera
• Characterize the image created by a camera

#### 14.7 The Simple Magnifier

• Understand the optics of a simple magnifier
• Characterize the image created by a simple magnifier

#### 14.8 Microscopes and Telescopes

• Explain the physics behind the operation of microscopes and telescopes
• Describe the image created by these instruments and calculate their magnifications