Chapter 19: Optics 19.1 Mirrors. The Law of Reflection The law of reflection states that the angle...

Chapter 19: OpticsChapter 19: Optics

19.1 Mirrors19.1 Mirrors

The Law of Reflection

The The law of reflectionlaw of reflection states that the angle of states that the angle of reflection is equal to reflection is equal to the angle of incidence.the angle of incidence.

The The angle of incidenceangle of incidence is the is the angle the incident ray makes angle the incident ray makes with a line drawn with a line drawn perpendicular to the surface perpendicular to the surface of the mirror. of the mirror.

The The angle of reflectionangle of reflection is the is the angle the reflected ray angle the reflected ray makes with the makes with the perpendicular line.perpendicular line.


The study of The study of opticsoptics assumes assumes that light is made up of rays that light is made up of rays that travel in straight lines. that travel in straight lines.

•A A ray diagramray diagram shows how rays shows how rays change direction when they change direction when they strike mirrors and pass strike mirrors and pass through lenses.through lenses.


The flat The flat ((planeplane) ) mirror and mirror and the mirror-the mirror-like lake like lake surface both surface both obey the law obey the law of reflection. of reflection.

The Law of Reflection Incident ray

Angle of incidence

Angle of refraction

Refracted ray

Plane Mirrors

A plane mirror always A plane mirror always produces a virtual produces a virtual image.image.

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

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

Plane Mirrors

Concave and Convex Mirrors

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

Convex mirrors Convex mirrors always cause light always cause light rays to spread out rays to spread out and can only form and can only form virtual images.virtual images.

Concave MirrorsConcave Mirrors

When the inside surface of a When the inside surface of a curved mirror is the reflecting curved mirror is the reflecting surface, the mirror is a surface, the mirror is a concave mirrorconcave mirror..

•The curvature of the reflecting The curvature of the reflecting surface causes the rays to surface causes the rays to come together.come together.

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

The type of image formed The type of image formed depends upon where the depends upon where the object is in relation to a object is in relation to a concave mirror.concave mirror.

– When object is farther from When object is farther from the mirror than focal point, the mirror than focal point, reflected rays meet in front reflected rays meet in front of the mirror to form a real of the mirror to form a real image.image.

Concave and Convex Mirrors

•A A real imagereal image is a is a copy of an copy of an object formed at object formed at the point where the point where light rays light rays actually meet. actually meet.

• Unlike a virtual image, a real image can be viewed on a surface such as a screen.

• The curvature of the convex mirror The curvature of the convex mirror causes the reflected rays to spread causes the reflected rays to spread out. The image formed by a convex out. The image formed by a convex mirror is always upright and smaller mirror is always upright and smaller than the object. than the object.

• Convex mirrors can only form virtual Convex mirrors can only form virtual images.images.

When the outside surface of a curved mirror is the reflecting surface, the mirror is a convex mirror.

Mirror ConnectionMirror Connection

Archimedes is said to have Archimedes is said to have burned the entire Roman fleet burned the entire Roman fleet by focusing the rays of the sun by focusing the rays of the sun with a huge curved mirror. with a huge curved mirror. Explain if this is possible and Explain if this is possible and what type of mirror it would what type of mirror it would have been.have been.

Assessment Questions

1.1. The image in a plane mirror The image in a plane mirror appears to be appears to be

a.a.in front of the mirror.in front of the mirror.

b.b.behind the mirror.behind the mirror.

c.c.in the plane of the mirror.in the plane of the mirror.

d.d.perpendicular to the plane of perpendicular to the plane of the mirror.the mirror.


2.2. A real image formed by a A real image formed by a mirror is mirror is a.a.always right-side up. always right-side up. b.b.always smaller than the always smaller than the

object.object.c.c.able to be projected on a able to be projected on a

screen.screen.d.d.only formed by convex only formed by convex

mirrors.mirrors.


3.3. An image of an object, formed by An image of an object, formed by a convex mirror, is always a convex mirror, is always

a.a.upright and smaller than the upright and smaller than the object.object.

b.b.upside down and smaller than upside down and smaller than the object.the object.

c.c. upright and larger than the upright and larger than the object.object.

d.d.upside down and larger than the upside down and larger than the object.object.


4.4. According to the law of According to the law of reflection, the angle of reflection, the angle of reflection is equal to the angle reflection is equal to the angle of incidence. of incidence.

TrueTrueFalseFalse

Chapter 19: OpticsChapter 19: Optics

19.2 Lenses19.2 Lenses

Concave and Convex Lenses

Concave lenses always Concave lenses always cause light rays to spread cause light rays to spread out and can only form out and can only form virtualvirtual images.images.

Convex lenses form either Convex lenses form either real or virtual images.real or virtual images.

Concave LensesConcave Lenses

A A lenslens is an object made of is an object made of transparent material that has transparent material that has one or two curved surfaces one or two curved surfaces that can refract light.that can refract light.

A A concave lensconcave lens is curved is curved inward at the center and is inward at the center and is thickest at the outside edges. thickest at the outside edges.

The rays enter the lens at The rays enter the lens at different angles, and so they different angles, and so they emerge from the lens at emerge from the lens at different angles.different angles.

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

•A concave lens forms a A concave lens forms a virtual image (always virtual image (always smaller than the object).smaller than the object).

A A convex lensconvex lens is curved is curved outward at the center and is outward at the center and is thinnest at the outer edges.thinnest at the outer edges.

•As the rays pass through As the rays pass through the lens, each one is the lens, each one is refracted, and they refracted, and they emerge at different emerge at different angles. angles.

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

• The converging rays meet The converging rays meet at the focal point, on the at the focal point, on the side of the lens opposite side of the lens opposite to the object.to the object.

Whether an image is real Whether an image is real or virtual depends upon or virtual depends upon how far the object is from how far the object is from the lens.the lens.

Concave and Convex Lenses

Lens QuestionLens Question

A magnifying glass is a simple A magnifying glass is a simple lens. Explain what type of lens lens. Explain what type of lens can be used as a magnifying can be used as a magnifying glass and draw a diagram glass and draw a diagram showing how light rays would be showing how light rays would be bent.bent.

Assessment Questions1.1. Light refracts when it passes from air Light refracts when it passes from air

to water because to water because

a.a. the wavelength is different in the the wavelength is different in the two media.two media.

b.b. the frequency is different in the two the frequency is different in the two media.media.

c.c. the speed is different in the two the speed is different in the two media.media.

d.d. the amplitude is different in the two the amplitude is different in the two media.media.


2.2. Which type(s) of lens can form Which type(s) of lens can form a real image? a real image? a.a.concave lens onlyconcave lens onlyb.b.convex lens onlyconvex lens onlyc.c.both concave and convex both concave and convex

lenseslensesd.d.neither concave nor convex neither concave nor convex

lenseslenses

Chapter 19: Optics 19.1 Mirrors. The Law of Reflection The law of reflection states that the angle...

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