Post on 04-Jan-2016
LENSES
Lyzinski Physics
Light Speeds
• When traveling through a vacuum, light travels at 3 x 108 m/s. This is the fastest light ever travels. We shall refer to this as the SPEED OF LIGHT.
• When traveling through a different “medium” (substance), light slows down.
• The INDEX OF REFRACTION compares this slower speed to the speed of light in a vacuum.
vcn
Index of refraction
Speed of light
Speed of light in new medium
The Index of Refraction
• What does “refract” mean. It means “to bend”. When light travels from one medium to another it actually bends (thus causing it to either slow down or speed up)
• The index of refraction is always GREATER THAN 1 (because the speed in a medium is always less than the speed of light).
• Optically “DENSE” mediums have a higher index. We will call these mediums “HEAVY”
• Optically “LESS DENSE” mediums will be called “LITE” (mis-spelled )
Some common mediums
Medium Index of Refraction
vacuum 1.00
air 1.003
water 1.33
ethanol 1.36
fluorite 1.43
crown glass 1.52
quartz 1.54
Zircon 1.92
diamond 2.42
Refraction (the bending of light)
i
r
i
r
n =1.00
n =1.33
air
water
n =1.52Crown glass
n =1.33water
If light goes from LITE to HEAVY, it bends TOWARD the normal.
If light travels from HEAVY into LITE, it bends AWAY FROM the normal
Normal to the surface
Normal to the surface
“La-Hite” (LHT) “Ha-La” (HLA)
Total Internal Reflection
orci nn 90sinsin
heavy
lite
Normal
“Ha-La” has a “Phenomena” associated with it.
ci
i
rc n
n1sin
Rrii nn sinsin
ci
SNELL’S LAW Relates the angles to the indexes
i
r
n =1.00
n =1.33
air
water
Normal to the surface
Rrii nn sinsin
How much does the light bend???
Prisms cause light to bend
glassairair
Light bends towards normal in the “heavy” glass
Light bends away from the normal in the “lite” air
IMPORTANT QUESTION: Does all light bend the same amount?
LHT HLA
All light does NOT bend the same amount in a prism.
Increasing index (bend)
Decreasing wavelength
Why does the index increase going from R to I (in ROY-G-BIV)?
The Wave Equation
The frequency of light never changes once it is created. Velocity can change. Wavelength will then also change. But frequency never changes once the wave is generated.
fv wavelength
frequencyWave speed
If v goes , then must go .
If v goes , n goes .
Refraction (the bending of light)
H
L
If light goes from LITE to HEAVY, it slows down AND the wavelength decreases.
If light travels from HEAVY into LITE, it speeds up AND the wavelength increases
Normal to the surface
L
H
Normal to the surface
Concave Lenses
Primary Focus
Principal axis
Concave lenses are similar to stacking two prisms.
Convex Lenses
Convex lenses are also similar to stacking two prisms.
Principal axisPrimary Focus
How do you locate the image formed in a LENSE Situation.
1. Any ray parallel to the principal axis is reflected through the focus.
2. Any ray through the focus is reflected parallel to the principal axis.
3. Any ray through the center of the lens passes directly through the lense following its same path.
Image Formation in CONVERGING Lenses
NO IMAGE!!!VIRTUAL!!!
Outside 2F’
2F’ F’
F 2F
On 2F’Between 2F’ & F’On F’Inside F’
Smaller, Inverted, RealLARGER, Inverted, Real
Same Size, Inverted, Real
Image Formation in Diverging Lenses
F
F’
All images are VIRTUAL and smaller than the object
Cameras ……
….. and the human eye
BOTH use converging
lenses with the object far
beyond the secondary
focus.
Film
Magnifying Glasses
2F’ F’ F 2F
Object that you are looking at (under the lens)
Larger, virtual image that you see
Film ProjectorsW
hite screen
Microscopes
Lens #1
(Objective)
Lens #2
(Eyepiece)
Virtual Image that your eye
sees
Human
eye
The Human EyeCornea: Protective “Window” of
eye
Iris: Colored part that acts like a
camera shutter.
Pupil: Hole in the middle of the
iris.
Lens: has adjustable focal length.
Retina: Where image is formed.
Optic nerve: Sends image to
brain where it is flipped
upside down.
Muscles that “tense” the lens
Near-Sightedness
Furthest Point that the eye can see
clearly
Far Point
Object beyond the far point can’t be focused clearly on the retina
“Fuzzy” vision
Diverging Lens creates a virtual image of the “far
away” object that is inside (or at) the far point. The eye
sees this virtual image clearly.
Far-Sightedness
Closest Point that the eye can see clearly
Near Point
Object inside the near point can’t be focused clearly on the retina
“Fuzzy” vision
Converging Lens creates a virtual image of the “too
close” object that is outside (or at) the near point. The eye sees this virtual image
clearly.
Focus of lens