1. Optics: Reflection, Refraction Mirrors and Lenses
05/25/2006
Optics
Mirrors and Lenses
Lecture 16

2. Reflection
Most things we see are thanks to reflections, since most objects don’t produce their own visible light. Much of the light incident on an object is absorbed but some is reflected. the wavelengths of the reflected light determine the colors we see. When white light hits an apple, for instance, primarily red wavelengths are reflected, while much of the others are absorbed.
A ray of light heading towards an object is called an incident ray. If it reflects off the object, it is called a reflected ray. A perpendicular line drawn at any point on a surface is called a normal (just like with normal force). The angle between the incident ray and normal is called the angle of incidence, i, and the angle between the reflected ray and the normal ray is called the angle of reflection, r. The law of reflection states that the angle of incidence is always equal to the angle of reflection.

3. 17.1 Reflection and Refraction
Key Question:
How do we describe the reflection and refraction of light?
*Students read Section AFTER Investigation 17.1

4. 17.1 Reflection
Images appear in mirrors because of how light is reflected by mirrors.
The incident ray follows the light falling onto the mirror.
The reflected ray follows the light bouncing off the mirror.

5. Law of Reflection The incident ray strikes the mirror.
The reflected ray bounces off.
The angle of incidence equals the angle of reflection.

6. 17.1 Law of reflection
30o
30o
1) You are asked for a ray diagram and the angle of reflection.
2) You are given the angle of incidence.
3) The law of reflection states the angle of reflection equals the angle of incidence.
4) The angle of reflection is 30°.
A light ray is incident on a plane mirror with a 30 degree angle of incidence.
Sketch the incident and reflected rays and determine the angle of reflection.

7. Optics: Reflection, Refraction
05/25/2006
Reflection
We describe the path of light as straight-line rays
Reflection off a flat surface follows a simple rule:
angle in (incidence) equals angle out (reflection)
angles measured from surface “normal” (perpendicular)
surface normal
same
angle
exit ray
reflected ray
incident ray
Lecture 16

8. Reflection Vocabulary
Real Image –
Image is made from “real” light rays that converge at a real focal point so the image is REAL
Can be projected onto a screen because light actually passes through the point where the image appears
Always inverted
Always drawn from reflected rays

9. Virtual Images in Plane Mirrors
Optics: Reflection, Refraction
                                    
05/25/2006
Virtual Images in Plane Mirrors
   
If light energy doesn't flow from the image, the image is "virtual".
Always formed by tracebacks
Rays seem to come from behind the mirror, but, of course, they don't.  It is virtually as if the rays were coming from behind the mirror. "Virtually":  the same as if As far as the eye-brain system is concerned, the effect is the same as would occur if the mirror were absent and the chess piece were actually located at the spot labeled "virtual image".
Lecture 16

10. Optics: Reflection, Refraction
05/25/2006
Curved mirrors
What if the mirror isn’t flat?
light still follows the same rules, with local surface normal
Parabolic mirrors have exact focus
used in telescopes, backyard satellite dishes, etc.
also forms virtual image
Lecture 16

11. View kacleaveland's map
"Have you ever approached a giant concave mirror? See your upside-down image suspended in mid-air. Walk through the image to see a new reflection, right-side-up and greatly magnified. In the background you see reflected a room full of visitors enjoying other
Taken in a place with no name (See more photos or videos here)
View kacleaveland's map
Concave Mirrors
Curves inward
May be real or virtual image

12. Optics: Reflection, Refraction
For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.
Optics: Reflection, Refraction
05/25/2006
For a real object between f and the mirror, a virtual image is formed behind the mirror. The image is upright and larger than the object.
Lecture 16

13. Optics: Reflection, Refraction
For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.
For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.
For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.
05/25/2006
For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.
Lecture 16

14. Optics: Reflection, Refraction
For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.
For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.
For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.
For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.
05/25/2006
For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.
Lecture 16

15. Optics: Reflection, Refraction
For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.
For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.
05/25/2006
For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.
Lecture 16

16. Optics: Reflection, Refraction
For a real object at f, no image is formed. The reflected rays are parallel and never converge.
05/25/2006
What size image is formed if the real object is placed at the focal point f?
For a real object at f, no image is formed. The reflected rays are parallel and never converge.
Lecture 16

17. Convex Mirrors Curves outward Reduces images Virtual images
Use: Rear view mirrors, store security…
CAUTION! Objects are closer than they appear!