Chapter 5 (2) Flashcards
Light
transfer of energy through alternating electric and magnetic fields
Photons
light emitted by electrons as they move from high to low energy states
Energy of photon
E= hf
h= planks
How can electron be excited
- by many high speed particles
- absorbing a photon of light
- thermal agitation
visible light range
390 x 10^-9 to 700 x 10^-9
shorter wavelengths correspond to violet light, longer wavelengths correspond to red light
Electromagnetic spectrum
long, radio, micro, infrared, UV, X ray, Gamma
Long has high wavelength low frequency
Gamma has low wavelength and high frequency
Speed of light
C= E/B= 3.00 x 10^8 m/s
ratio of electric field to magnetic field
What causes light absorption
depends on medium and frequency of the wave as they move
absorbed when frequency matches resonant frequency of the medium
polarized light
electric and magnetic fields are oriented in a certain way
refraction
light bending as it passes into a new medium
usually a lens
dispersion
splitting of light according to a frequency
diffraction
spreading of light as it encounters an edge (interference when passing through a slit)
depends on size of object or opening relative or wavelength
Angle of incidence
how light strikes a boundary/ interface
What happens when light reflects off a flat surface
angle of incidence (strike) equals angle of reflection
What affects refraction
depends on how speed of light changes when it enters a new medium
index of refraction
n= c/v
light is slower in a medium
c= speed of light in a vacuum, v= speed of light in a medium
always greater than 1
What does a larger index of refraction mean
light moves more slowly through a medium
wavelength becomes shorter
Snells law
n1sin theta1= n2sin theta2
predicts how change in speed will bend a light ray
theta 1 is incidence, theta 2 is refraction
What happens when light moves from higher index to lower index of refraction
light begins to move faster and spreads out
light bends away from normal (perpendicular to surface)
Total internal reflection
caused when light comes from a higher index and the angle is very large
none refract, all reflect (critical angle is reached)
critical angle formula
thata= sin-1 (n2/n1)
thin film interference
thin layer with a different index placed between two layers
-refracts: changes wavelength
-Reflects off denser: changes phase
- reflects off less dense: changes neither
what causes thin film interference
phase change due to reflections off more dense
path length differences
wavelength changes associates with changes in media
When is diffraction significant
size of an object or opening
is small relative to the wavelength
How does deffracted light appear
constructive interference is bright, destructive is dark
X ray diffraction
uses atoms of crystals to act as a natural diffraction grating
X rays scatter and create regular interference patterns
thin lens
maximal thickness is small relative to the radius of curvature, object distance and image distance
focal point
parallel light rays converge or appear to converge after reflecting off a mirror or passing through a lens
real focus point
point at which light rays actually converge
virtual focal point
point at which light appears to converge
center of curvature
each point along mirrors surface is equidistant from center of curvature
radius of curvature
distance between surface of mirror and center of curvature
smaller=sharper curve
where is the focal point on a convex and concave mirror
concave focal point is front of mirror, convex focal point is behind the mirror
focal length
distance between a mirror and its focal point
F=R/2
r= radius of curvature
Lens strength
power, determined by focal length
p=1/f
Use F in meters
Signs for focal length
positive= light travels to the focal point, convergers
negative= light does not actually travel there, divergers
converging mirrors
reflect light to converge in front of mirror
concave
converging lens
refracts light rats to converge at a point opposite the light source
convex
behavior of diverging
spread out so that light rays never intersect
diverging mirror
reflects light rays so that observer perceives them as converging on the opposite side of the mirror
convex
diverging lens
refracts light so that they appear to converge at a point on the same side of the lens as the light source
concave
Real image
from convergence of light rays
inverted, on same side as observer, positive
virtual image
cannot be captured on a screen
produced by the apparent convergence of light rays
opposite, negative, upright, from diverging or converging
When is a converger virtual vs. real
when object is located beyond the focal point, convergers make a real image (COMMON)
when object is placed within focal point, image is virtual (object is between focal point and mirror/lens)
thins lens equation
relates image distance (di) from the mirror/lens and the object distance (d0) to the focal length
uses cm
1/f= 1/do + 1/di
or use p as do and q as di
signs for focal distance
converging is positive, diverging is negative
signs for object distance
positive if in right location
same side of observer for mirrors, opposite for lens
signs for image distance
positive if real, negative if virtual
p=f
no image is formed
magnification
m= -(di/do)= (hi/ho)
How do divergers magnify
always produce images that are smaller than object
lens abberation
blurred images from theoretical images
multiple lens magnification
m= m1*m2
multiple lens power
Peff= P1 + P2…
how does light work in eye
refracts incoming light so that it focuses on the area at the back of eye (retina)
What parts of the eye bend light
cornea (bends the most) and the lens
bend light to converge at retina
how does the eye focus light on near objects
muscle surrounding the lens contracts causing the lens to bulge and reducing the focal length of the lens
myopia (what is it, how does it work improperly)
near sighted, see near objects clearly
good at bending light to focus on retina – bends light of far objects too sharply and converges in front of retina
hyperopia
far sighted, cannot bend light properly
Far light rays are more parallel (do not need to be bent)
nearby rays are not bent- converges rays passed the retina
How is myopia corrected
correct with diverging lens (spreads out light rays to focus on retina)
how is hyperopia corrected
using a converging lens to make light rays closer to parallel
