1. Physics 1 L Created by Stephanie Ingle Tweaked by Rex Wolf
Light Waves
Physics 1 L
Created by Stephanie Ingle
Tweaked by Rex Wolf

2. Light Light is a transverse wave.
Light waves are electromagnetic waves--which means that they do NOT need a medium to travel.
Light waves behave like other waves and have the same characteristics such as amplitude, frequency, and wavelength.

3. Characteristics of Light
Intensity (brightness) -- represented by amplitude
Color -- determined by frequency
Wave speed - depends on the medium
Light waves as well as ALL Electromagnetic waves travel with a speed of 3.0 x 108 m/s in a vacuum.
Recall: v = f l

4. Luminous vs Illuminated
a body that reflects light
does not emit light of its own
Luminous
a body that emits light
Types of Reflection
Regular Reflection
When parallel rays of light fall on a smooth surface they are reflected parallel from the surface.
Diffuse Reflection
When parallel rays of light fall on a textured surface they are reflected in many different directions. They are diffused.

5. Reflection & Mirrors

6. Law of Reflection i
incident ray
reflected ray
normal
Mirror surface r
Angles are always measured from the normal, never the surface
Angle of incidence equal angle of reflection
i = r

7. Concave Mirrors
Reflective surface to the inside of curve, forms a “cave”
Parallel rays of light from a far object will converge at the focal point.
Concave Mirrors also called “converging mirrors”
Focal point is half the distance from the center of curvature (C) to the mirror
f = R/2, where R is radius of curvature

8. Convex Mirrors
Reflective surface to the outside of curve (back of spoon)
Parallel rays of light from a far object will diverge as if they originated at the focal point.
Convex Mirrors also called “diverging mirrors”
Focal point is half the distance from the center of curvature (C) to the mirror
f = R/2, where R is radius of curvature

9. Calculations f = focal length do = object distance di = image distance
hi = image height
ho = object height
M = magnification

10. Interpreting Calculations
Focal length (f)
converging, then f = + diverging, then f = -
Image distance (di)
di=+ , then image is real
di= -, then image is virtual
Magnification (M)
M = +, image is upright
M = - , image is inverted

11. Example 1
A concave spherical mirror has a radius of curvature of 20.0 cm. Locate the image of a pencil that is placed upright 30.0 cm from the mirror. Find the magnification of the image.

12. Example 2
A concave spherical mirror has a radius of curvature of 30.0 cm. Locate the image of a pencil that is placed upright 5.0 cm from the mirror. Find the magnification of the image.

13. Example 3
An upright pencil is placed in front of a convex spherical mirror with a focal length of 8.0cm. An upright image 2.50 cm tall is formed 4.44 behind the mirror. Find the position of the object, the magnification of the image, and the height of the pencil.

14. Concave Mirror (object beyond C)
Ray Diagram
Concave Mirror (object beyond C)
Draw 2 rays from tip of object:
1) parallel, then through f
2) through f, then parallel
object
Image is real, inverted, & reduced
image C f

15. Concave Mirror (object at C)
Ray Diagram
Concave Mirror (object at C)
Draw 2 rays from tip of object:
1) parallel, then through f
2) through f, then parallel
object
Image is real, inverted, & same size C
image f

16. Concave Mirror (object between f & C)
Ray Diagram
Concave Mirror (object between f & C) f C
object
image
Draw 2 rays from tip of object:
1) parallel, then through f
2) through f, then parallel
Image is real, inverted, & magnified

17. Ray Diagram Concave Mirror (object inside f)
Draw 2 rays from tip of object:
1) parallel, then through f, extend reflected ray behind mirror.
2) through f as if it came from focal point, then parallel, extend reflected ray behind mirror
image C
object f
Image is virtual, erect, & magnified

18. Ray Diagram Convex Mirror
Draw 2 rays from tip of object:
1) parallel, then reflect as if ray came from f, ) toward focal point, then parallel, extend reflected ray behind mirror
image
object f C
Image is virtual, erect, & reduced

19. Electromagnetic Spectrum
low freq, high l
Radio
Microwaves
Infrared
Visual (light)
Ultraviolet
X-rays
Gamma Rays
Red
Orange
Yellow
Green
Blue
Indigo
Violet
high freq, low l
red martians invade venus using x-ray guns
ROY G BIV

20. Examples Which has a higher frequency, green light or red light?
Which has a higher wavelength, orange light or microwaves?
Which has a lower frequency, gamma rays or infrared?
Which has a lower wavelength, radio waves or ultraviolet waves?
Which travels faster, yellow light or x-rays?

21. PreQuiz Example
Bob the bulldog is 50cm tall. His virtual image is 100cm tall, upright, and 30 cm from the mirror.
Find magnification
Where is Bob?
Find focal length.
Is the mirror concave or convex?

22. Glass sphere? Lawn sphere?

23. Equations