LENSES Lyzinski Physics

Light Speeds When traveling through a vacuum, light travels at 3 x 10 8 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. 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 MediumIndex of Refraction vacuum1.00 air1.003 water1.33 ethanol1.36 fluorite1.43 crown glass1.52 quartz1.54 Zircon1.92 diamond2.42

Refraction (the bending of light) n =1.00 n =1.33 air water n =1.52 Crown glass n =1.33 water 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 “ La-Hite” (LHT) “ Ha-La” (HLA)

Total Internal Reflection heavy lite Normal “Ha-La” has a “Phenomena” associated with it.

SNELL’S LAW Relates the angles to the indexes n =1.00 n =1.33 air water Normal to the surface How much does the light bend???

Prisms cause light to bend glass air 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. wavelength frequency Wave 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

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 axis Primary 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, Real LARGER, 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 Projectors White screen

Microscopes Lens #1 (Objective) Lens #2 (Eyepiece) Virtual Image that your eye sees Human eye

The Human Eye Cornea: 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