Chapter 19 – Optics Chapter 19 – Optics

Jennie L. BordersJennie L. Borders

Section 19.1 - MirrorsSection 19.1 - Mirrors

OpticsOptics is the study of how is the study of how mirrors and mirrors and lenseslenses form images. form images.

A A ray diagramray diagram shows how rays change shows how rays change directiondirection when they strike when they strike mirrorsmirrors and and pass through pass through lenseslenses..

The The incoming rayincoming ray, called the , called the incident rayincident ray, , approaches the mirror.approaches the mirror.

The Law of ReflectionThe Law of Reflection

The The angle of incidenceangle of incidence is the angle the is the angle the incident rayincident ray makes with a line drawn makes with a line drawn perpendicularperpendicular to the surface of the to the surface of the mirrormirror..The The angle of reflectionangle of reflection is the angle the is the angle the reflected rayreflected ray makes with the perpendicular makes with the perpendicular line.line.The The law of reflectionlaw of reflection states that the angle states that the angle of of reflectionreflection is equal to the angle of is equal to the angle of incidenceincidence..

Ray DiagramRay Diagram

surface normal

sameangleincident ray exit ray

reflected ray

Plane MirrorsPlane MirrorsA mirror with a A mirror with a flatflat shiny surface is a shiny surface is a plane plane mirrormirror..

When you look into a When you look into a plane mirrorplane mirror, you , you see your see your reversed reflectionreversed reflection, a right-left , a right-left reversed image of yourself.reversed image of yourself.

An An imageimage is a copy of an is a copy of an objectobject formed by formed by rays of rays of lightlight..

Plane MirrorsPlane MirrorsTo produce your To produce your imageimage in a mirror, rays of in a mirror, rays of light strike you andlight strike you and reflect reflect. These reflected . These reflected rays then strike the rays then strike the mirrormirror and are and are reflectedreflected into your eyes. into your eyes.

Your Your imageimage appears the same appears the same distancedistance behind the behind the mirrormirror as you are in front, and as you are in front, and the image is the image is right side upright side up..

Plane MirrorsPlane Mirrors

A A plane mirrorplane mirror always produces a always produces a virtual virtual imageimage..

Although you can see a Although you can see a virtual imagevirtual image, this , this type of image cannot be type of image cannot be projectedprojected onto onto any surface.any surface.

A A virtual imagevirtual image is a copy of an is a copy of an objectobject formed at the location from which the light formed at the location from which the light rays rays appearappear to come. to come.

Concave MirrorsConcave MirrorsWhen the When the insideinside surface of a surface of a curved mirrorcurved mirror is the reflecting surface, the mirror is a is the reflecting surface, the mirror is a concave mirror.concave mirror.

The The curvaturecurvature of the reflecting surface of the reflecting surface causes the rays to causes the rays to come togethercome together..

The The pointpoint at which the at which the light rays meetlight rays meet is is called the called the focal pointfocal point..

Concave MirrorsConcave MirrorsA A real imagereal image is the copy of an is the copy of an objectobject formed at the point where light rays formed at the point where light rays actuallyactually meet. meet.

Unlike a Unlike a virtual imagevirtual image, a , a real imagereal image can be can be viewed on a surfaceviewed on a surface such as a screen. such as a screen.

Concave mirrorsConcave mirrors can form either can form either real or real or virtual imagesvirtual images..

Real ImageReal Image

When the object is When the object is fartherfarther from the mirror from the mirror than the than the focal pointfocal point, the reflected rays , the reflected rays meet in meet in frontfront of the mirror, making a of the mirror, making a real real imageimage..

Virtual ImageVirtual ImageWhen the object is When the object is closercloser to the mirror to the mirror than the than the focal pointfocal point is the reflected rays is the reflected rays spread out and appear to come from spread out and appear to come from behindbehind the mirror, making a the mirror, making a virtual imagevirtual image..

Convex MirrorsConvex MirrorsWhen the When the outsideoutside surface of a surface of a curved curved mirrormirror is the reflecting surface, the mirror is the reflecting surface, the mirror is a is a convex mirrorconvex mirror..

The curvature of the The curvature of the convex mirrorconvex mirror causes causes the reflected rays to the reflected rays to spread outspread out..

Convex MirrorsConvex Mirrors

Convex mirrorsConvex mirrors always cause light rays to always cause light rays to spread outspread out and can only form and can only form virtual virtual imagesimages..

The image formed by a The image formed by a convex mirrorconvex mirror is is always always uprightupright and and smallersmaller than the object. than the object.

Section 19.1 AssessmentSection 19.1 Assessment

How is the angle of incidence of a light ray How is the angle of incidence of a light ray related to the angle of reflection?related to the angle of reflection?

What type of image does a plane mirror What type of image does a plane mirror form?form?

What types of image can be produced by What types of image can be produced by a concave mirror? A convex mirror?a concave mirror? A convex mirror?

How are real images different from virtual How are real images different from virtual images?images?

Section 19.1 AssessmentSection 19.1 Assessment

If you place an object 10 cm from a If you place an object 10 cm from a particular concave mirror, a virtual image particular concave mirror, a virtual image forms behind the mirror. What can you forms behind the mirror. What can you infer about the focal point of the mirror?infer about the focal point of the mirror?

If you look inside the bowl of a shiny metal If you look inside the bowl of a shiny metal spoon, your image is upside down. If you spoon, your image is upside down. If you look at the outside of the spoon’s bowl, look at the outside of the spoon’s bowl, your image is right side up. Explain.your image is right side up. Explain.

Section 19.2 - LensesSection 19.2 - Lenses

Light usually travels in Light usually travels in straight linesstraight lines..

When light enters a When light enters a new mediumnew medium at an at an angleangle, the change in , the change in speedspeed causes the causes the light to light to bend, or refractbend, or refract..

Index of RefractionIndex of Refraction

How much the How much the speedspeed of a light ray slows of a light ray slows as it enters a as it enters a new materialnew material depends on the depends on the material’s material’s index of refractionindex of refraction..

The The index of refractionindex of refraction for a material is the for a material is the ratio of the ratio of the speed of light in a vacuumspeed of light in a vacuum to to the the speed of light in the materialspeed of light in the material..

A material with a A material with a lowlow index of refraction index of refraction causes light to slow and refract very little.causes light to slow and refract very little.

Index of RefractionIndex of Refraction

LensesLenses

A A lenslens is an object made of is an object made of transparenttransparent material that has one or two material that has one or two curved surfacescurved surfaces to refract light.to refract light.

Concave LensesConcave Lenses

A A concave lensconcave lens (diverging lens) is curved (diverging lens) is curved inwardinward at the center and is at the center and is thickestthickest at the at the outside edges.outside edges.

Concave lensesConcave lenses cause incoming parallel cause incoming parallel rays to rays to spread outspread out, or diverge., or diverge.

Concave LensesConcave LensesConcave lensesConcave lenses always cause light rays to always cause light rays to spread outspread out and can only form and can only form virtual virtual imagesimages..

The The imageimage formed by a concave lens is formed by a concave lens is always always smallersmaller than the object. than the object.

Convex LensesConvex LensesA A convex lensconvex lens (converging lens) is curved (converging lens) is curved outwardoutward at the center and is at the center and is thinnestthinnest at the at the outer edges.outer edges.

Convex lensesConvex lenses cause incoming parallel cause incoming parallel rays to rays to come togethercome together, or converge., or converge.

Convex LensesConvex Lenses

The converging rays The converging rays meetmeet at a single at a single point, the point, the focal pointfocal point, on one side of the , on one side of the lens opposite the object.lens opposite the object.

Convex lensesConvex lenses form either form either real or virtual real or virtual imagesimages..

Virtual image

Convex LensesConvex Lenses

Real image

Concave vs. ConvexConcave vs. Convex

Fiber OpticsFiber Optics

Light raysLight rays are generally unable to exit are generally unable to exit through the sides of the curving through the sides of the curving fiber opticfiber optic strands.strands.

Because of this, Because of this, fiber opticsfiber optics are very are very useful for carrying information in the form useful for carrying information in the form of of lightlight..

Total Internal ReflectionTotal Internal Reflection

The The critical anglecritical angle is the is the angle of incidenceangle of incidence that produces an that produces an angle of refractionangle of refraction of 90 of 90 degrees.degrees.

Total internal reflectionTotal internal reflection is the complete is the complete reflection of a light ray back into its reflection of a light ray back into its original original mediummedium..

Total Internal ReflectionTotal Internal Reflection

Materials that have Materials that have smallsmall critical angles critical angles are likely to cause most of the light are likely to cause most of the light entering them to be entering them to be totally internally totally internally reflectedreflected..

Such materials include Such materials include diamonddiamond and the and the type of type of glassglass used in fiber optics. used in fiber optics.

Section 19.2 AssessmentSection 19.2 Assessment

What causes light rays to bend?What causes light rays to bend?

Why can concave lenses only form one Why can concave lenses only form one type of image?type of image?

What type of images are formed by What type of images are formed by concave lenses? By convex lenses?concave lenses? By convex lenses?

How is a convex lens different from a How is a convex lens different from a concave lens? How are they the same?concave lens? How are they the same?