1. Physics 1 H Created by Ingle
Light Waves
Physics 1 H
Created by Ingle
Stephanie

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.

4. Characteristics of Electromagnetic Waves
Made up of 2 components
electric field & magnetic field
The electric and magnetic fields are perpendicular to each other.
A changing electric field will create a magnetic field and a changing magnetic field will create an electric field; therefore the wave propagates itself through space without need of a medium.

5. Other Electromagnetic Waves
Radio
Microwaves
Infrared
Ultraviolet
X-rays
Gamma Rays
Radar
All of these follow the same rules as Light and travel at the same speed.
Light is simply a way of referring to the visible portion of the electromagnetic spectrum.

6. Luminous vs Illuminated
a body that emits light
has luminous flux
Illuminated
a body that reflects light
no luminous flux
does not emit light of its own

7. Luminous Flux (P)
Luminous flux is the rate at which light energy is emitted from the source.
Equivalent to Power
Measured in lumens (lm)

8. Luminous Intensity (I)
The amount of light (luminous flux) that falls on one square meter at a distance of 1 meter from the source.
Equivalent to Intensity at r = 1 m
Measured in candelas (cd)
I = P/4 or cd = lm/4

9. Illuminance (E) E = P/(4r2) Amount of light that falls on a surface
Intensity of light at any given distance from source
measured in lux
lux = lumen/m2 r
bulb
E = P/(4r2)

10. Reflection & Mirrors

11. 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

12. Types of Reflection Regular Reflection Diffuse 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.

13. 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

14. 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

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

16. 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 erect
M = - , image is inverted

17. 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

18. 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

19. 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

20. 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

21. 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