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Light Waves
Physics 1 H
Created by Stephanie Ingle
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.
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.
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.
Electromagnetic Waves
•
•
•
•
•
•
•
Radio
Microwaves
Infrared
Visible Light
Ultraviolet
X-rays
Gamma Rays
• All of these follow the same
rules as Light and travel at
the same speed.
• They are listed in order of
increasing frequency and
energy and decreasing
wavelength
• Light is the visible part of
the spectrum
Luminous vs Illuminated
• Luminous
– a body that
emits light
– has luminous
flux
• Illuminated
– a body that
reflects light
– no luminous
flux
– does not emit
light of its own
Luminous Flux (P)
• Luminous flux is the rate at
which light energy is emitted
from the source.
• Equivalent to Power
• Measured in lumens (lm)
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
P
I
4
Illuminance (E)
• Amount of light that falls on a
surface
• Intensity of light at any given
distance from source
• measured in lux
r
• lux = lumen/m2
P
E
2
4 r
bulb
Reflection & Mirrors
Law of Reflection
normal
incident ray
Mirror surface
reflected ray
i
r
• Angles are always measured from the normal,
never the surface
• Angle of incidence equal angle of reflection
• i = r
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.
Concave Mirrors
• Reflective surface, like inside of a spoon,
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
Convex Mirrors
• Reflective surface, like back of a spoon or
outside of curve
• 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
Calculations
1 1 1
f do di
h
i

d
i
M 
ho do
f = focal length
do = object distance
di = image distance
hi = image height
ho = object height
M = magnification
Interpreting Calculations
Focal length (f)
concave or converging, then f is +
convex or diverging, then f is Image distance (di)
di is + , then image is real
di is -, then image is virtual
Magnification (M)
M = +, image is erect and virtual
M = - , image is inverted and real
Ray Diagram
Concave Mirror (object beyond C)
Draw 2 rays from tip of object:
1) parallel, then through f
2) through f, then parallel
The image is formed where the reflected rays intersect.
object
Image is
real,
inverted, &
reduced
image
C
f
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
Ray Diagram
Concave Mirror (object between f & C)
Draw 2 rays from tip of object:
1) parallel, then through f
2) through f, then parallel
Image is real,
inverted, &
magnified
object
C
image
f
Ray Diagram
Concave Mirror (object inside f)
Draw 2 rays from tip of object:
1) parallel, then through f
2) as if it came from the focal
point and then parallel
3) extend the reflected rays
behind mirror to locate
image
image
C
f object
Image is virtual, erect, & magnified
Ray Diagram
Convex Mirror
Draw 2 rays from tip of object:
1) parallel, then reflect as
if ray came from focus
2) toward the focal point,
then parallel
3) extend the reflected rays
behind the mirror to locate
the image
object
Image is virtual, erect, & reduced
image
f
C