Light and Optics

Light and OpticsLight and Optics

What Can You Discover About Light?What Can You Discover About Light?

• Using the supplies that you have been given, make Using the supplies that you have been given, make some of your own discoveries about light and draw some of your own discoveries about light and draw diagrams with explanations showing what you diagrams with explanations showing what you discovered. You don’t need to know “why” you are discovered. You don’t need to know “why” you are seeing what you are seeing, only “what”.seeing what you are seeing, only “what”.

• (Show demo of refraction with laser and broken stir (Show demo of refraction with laser and broken stir stick)stick)

• (Try the optic nerve activity with Tweety and (Try the optic nerve activity with Tweety and Sylvester) Sylvester)

Spring 2006

UCSD: Physics 8; 2006

2

Light and Color – Bill NyeLight and Color – Bill Nye

• http://www.youtube.com/watch?v=gtgBHsSzCPEhttp://www.youtube.com/watch?v=gtgBHsSzCPE

Spring 2006


3

1.1 Human Understanding of Light1.1 Human Understanding of Light

• Using your textbook (pgs. 176-181), create a timeline Using your textbook (pgs. 176-181), create a timeline documenting the important discoveries about light documenting the important discoveries about light throughout human history. Be sure to include who the throughout human history. Be sure to include who the person/people involved are, and what they person/people involved are, and what they discovered.discovered.

Spring 2006


4

1.2 Optical Devices1.2 Optical Devices

• An An Optical Device Optical Device is any technology that uses light.is any technology that uses light.• 2 common optical devices are Microscopes (make 2 common optical devices are Microscopes (make

small objects bigger) and Telescopes (make far small objects bigger) and Telescopes (make far objects closer).objects closer).

• Microscopes – use at least Microscopes – use at least

2 lenses to increase the size2 lenses to increase the size

of an object.of an object.

Spring 2006


5

Optical DevicesOptical Devices

• Refracting telescopes Refracting telescopes – use 2 different sized lenses – use 2 different sized lenses to to collect and magnify collect and magnify light in order to make it seem light in order to make it seem like an object is larger than it is.like an object is larger than it is.

Spring 2006


6

Optical DevicesOptical Devices

• Reflecting telescopes Reflecting telescopes – use 2 different sized mirrors – use 2 different sized mirrors (one curved inwards) to (one curved inwards) to collect and magnify light collect and magnify light in in order to make it seem like an object is larger than it order to make it seem like an object is larger than it is.is.

Spring 2006


7

2.1 Ray Diagram and the Path of Light2.1 Ray Diagram and the Path of Light

• Light always travels in straight lines from a light Light always travels in straight lines from a light sourcesource

• A Ray Diagram shows the direction that light travels A Ray Diagram shows the direction that light travels using an arrow to indicate the direction of travel. using an arrow to indicate the direction of travel.

• It travels in all directions until it is something gets in It travels in all directions until it is something gets in its way. The object will either reflect the light, absorb its way. The object will either reflect the light, absorb it or else allow the light to pass through it.it or else allow the light to pass through it.

Spring 2006


8

Examples of Ray DiagramsExamples of Ray Diagrams

The arrow indicates the direction light travelsThe arrow indicates the direction light travels

Spring 2006


9

Ray Diagram and the Path of Light – Ray Diagram and the Path of Light – Cont.Cont.

• Opaque objects – Allow no light to pass though and Opaque objects – Allow no light to pass though and absorb or reflect light that hits it absorb or reflect light that hits it

• Ex – Ex –

• Translucent Objects – Allow some light to pass Translucent Objects – Allow some light to pass through and some is absorbedthrough and some is absorbed

• Ex –Ex –• Transparent Objects – Allow all light to pass though Transparent Objects – Allow all light to pass though

themthem• Ex - Ex -

Spring 2006


10

Ray Diagram and the Path of Light – Ray Diagram and the Path of Light – Cont.Cont.

• Any object that emits its own light is said to be a Any object that emits its own light is said to be a LUMINOUSLUMINOUS object. object.

• Some examples of natural luminous objects are:Some examples of natural luminous objects are:

• Some examples of human made luminous objects Some examples of human made luminous objects are:are:

• Any object that reflects light but DOES NOT Any object that reflects light but DOES NOT PRODUCE IT is said to be a PRODUCE IT is said to be a NON-LUMINOUSNON-LUMINOUS object object

• Some examples of non-luminous objects are:Some examples of non-luminous objects are:

Spring 2006


11

Reflection LabReflection Lab

• Reflection Lab.notebookReflection Lab.notebook• Reflection Lab Finished.notebookReflection Lab Finished.notebook

Spring 2006


12

ReflectionReflection• We describe the path of light as straight-line raysWe describe the path of light as straight-line rays• Reflection off a flat surface follows a simple rule:Reflection off a flat surface follows a simple rule:

– angle in (incidence) equals angle out (reflection)– angles measured from surface “normal” (perpendicular)

• (Show Echalk reflection example)(Show Echalk reflection example)

surface normal

sameangleincident ray exit ray

reflected ray

Regular and Diffuse ReflectionRegular and Diffuse Reflection

Spring 2006


14

Curved mirrorsCurved mirrors

• What if the mirror isn’t flat?What if the mirror isn’t flat?– light still follows the same rules, with local surface normal– used in telescopes, backyard satellite dishes, etc.– also forms virtual image (an image that is not real)

ConvexConvex Mirrors Mirrors

• Curves outward• Smaller images but more can be seen• Virtual images – image is always right side up!!!

– Use: Rear view mirrors, store security…

CAUTION! Objects are closer than they appear!

Concave MirrorsConcave Mirrors•Curves inward•May be real or virtual image

82a425d700

Spring 2006


18

For a real object between f and the mirror, a For a real object between f and the mirror, a virtual image is formed behind the mirror. The virtual image is formed behind the mirror. The image is upright and larger than the object. image is upright and larger than the object.

For a real object between f and the mirror, a virtual image is formed behind the mirror. The position of the image is found by tracing the reflected rays back behind the mirror to where they meet. The image is upright and larger than the object.


For a real object close to the mirror but outside of the center of curvature, the real image is formed between C and f. The image is inverted and smaller than the object.

For a real object between C and f, a real image is formed outside of C. The image is inverted and larger than the object.





For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.

For a real object at C, the real image is formed at C. The image is inverted and the same size as the object.




For a real object at f, no image is formed. The reflected rays are parallel and never converge.

For a real object at f, no image is formed. The reflected rays are parallel and never converge.

What size image is formed if the real object is placed at the focal point f?

RefractionRefraction• Light also goes Light also goes throughthrough some things some things

– glass, water, eyeball, air

• The presence of material slows light’s progressThe presence of material slows light’s progress– interactions with electrical properties of atoms

• The “light slowing factor” is called the The “light slowing factor” is called the index of refractionindex of refraction– glass has n = 1.52, meaning that light travels about 1.5 times

slower in glass than in vacuum– water has n = 1.33– air has n = 1.00028– vacuum is n = 1.00000 (speed of light at full capacity)

Refraction LabRefraction Lab

• Refraction Lab.notebookRefraction Lab.notebook

Spring 2006


25

n2 = 1.5

n1 = 1.0

A

B

Refraction at a plane surfaceRefraction at a plane surface• Light bends at interface between refractive indicesLight bends at interface between refractive indices

– bends more the larger the difference in refractive index

• (Show Echalk refraction example)(Show Echalk refraction example)

Video on the effects of refractionVideo on the effects of refraction

• http://www.youtube.com/watch?v=kc2o73FyN3Ihttp://www.youtube.com/watch?v=kc2o73FyN3I• 5:37 – 9:105:37 – 9:10

Convex LensesConvex Lenses

Thicker in the center than Thicker in the center than edges. edges. – Lens that converges

(brings together) light rays.

– Forms real images and virtual images depending on position of the object

– Images can be flipped and/or larger depending on the position of the lens

The Magnifier

Concave LensesConcave Lenses

• Lenses that are Lenses that are thicker at the edges thicker at the edges and thinner in the and thinner in the center. center. – Diverges light rays

(spreads them apart)

– All images arereduced or smaller because less light is hitting your eye

The De-Magnifier

Practice!Practice!

• Worksheet on Reflection and RefractionWorksheet on Reflection and Refraction

Spring 2006


30

The Human EyeThe Human Eye

Spring 2006


31

The Human EyeThe Human Eye

Spring 2006


32

How You See How You See

• Near Sighted – Eyeball is Near Sighted – Eyeball is too long and image focuses too long and image focuses in front of the retinain front of the retina

• Near Sightedness – Concave lenses expand focal length

• Far Sighted – Eyeball is too Far Sighted – Eyeball is too short so image is focused short so image is focused behind the retina.behind the retina.

• Far Sightedness – Convex lense shortens the focal length.

Eye Dissection Eye Dissection

• coweye dissection.pdfcoweye dissection.pdf

Spring 2006


34

Cameras, in briefCameras, in brief

In a pinhole camera, the hole is so small that light hitting any particular pointon the film plane must have come from a particular direction outside the camera

In a camera with a lens, the same applies: that a point on the film planemore-or-less corresponds to a direction outside the camera. Lenses havethe important advantage of collecting more light than the pinhole admits

pinholeimage atfilm plane

object

image atfilm plane

object

lens

Review QuizReview Quiz

• Light Rays Question Set.notebookLight Rays Question Set.notebook

Spring 2006


36

Documents

Light and Optics