Chapter 17: Reflection and Mirrors

BIG IDEA: All surfaces reflect light, but smooth surfaces can produce images.

Section 17.1 Plane Mirrors

Section 17.2 Curved Mirrors

Table Of ContentsCHAPTER

17

Mirrors: History and production

SECTION17.1

Plane MirrorsLAW OF REFLECTION

The angle that a reflected ray makes us measured from normal to a reflective surface equals the angle that the incident ray makes as measured from the same normal.

See animation

Rough vs smooth surface Rough surface: has normals that are not parallel so incidence ray are not reflected in parallel ( diffuse reflection)Smooth surface: has parallel normals so incident rays are reflected in parallel (specular reflection)

The image of the light bulb is reflected on the table by the smooth mirror while the paper reflects a featureless area of light

Objects and plane mirror images

plane mirror is a flat, smooth surface from which light is reflected by specular reflection•Light from the lamp is reflected from the boy to the mirror (diffuse reflection).•Mirror reflects light to the boy’s eye enabling him to see an image of himself (specular reflection)

How is the Boy illuminated? - by light directly from the lamp and by light directly from the mirror

Properties of plane mirror imagesRays that reflect from the bird will disperse in many directions. Only a few that travel toward the mirror are shown. The image is located where multiple light rays from a point on an object seem to converge.

Image position and heightPlane mirror image positionImage position = - image position (behind the mirror or virtual image)Plane mirror image heightImage height = object’s height

Image OrientationPlane Mirrors reverse the boy’s image producing a front-to-back reversal (flipped horizontally not vertically).

Summing up: Plane Mirrors• An image produced by a plane mirror is

always virtual, is the same size of the object, has the same orientation, and is the same distance from the mirror as the object

Problem solving page 467

Section 17.2 Curved Mirrors

Table Of ContentsCHAPTER

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MAIN IDEACurved mirrors can produce real and virtual images and can magnify or reduce the image size.

SECTION17.2

Curved Mirrors

• reflection is different from what a plane mirror.

• one side curved inward and the other curved outward.

• The properties of curved mirrors and the images that they form depend on the shape of the mirror and the object’s position.

Properties of Curved MirrorsSECTION17.2

Curved Mirrors

• has a reflective surface, the edges of which curve toward the observer.

• inside surface of spoon: concave mirror.

• Properties of a concave mirror depend on how much it is curved.

Concave mirrorSECTION17.2

Curved Mirrors

• spherical concave mirror: shaped like a section of a hollow sphere with an inner reflective surface, has the same geometric center (C), and radius of curvature (r), as a sphere of radius, r.

• principal axis - line that passes through line segment CM and divides the mirror in half.

SECTION17.2

Curved MirrorsProperties of Curved Mirrors

Ray Diagram for concave mirrors

Ray diagrams can be used to locate an image reflected from a curved mirror.See animation

Practical uses of concave mirror• Behind light bulbs in theater spotlights and car

headlights, telescopes (for precise focusing)

SECTION17.2

Curved MirrorsProperties of Curved Mirrors

Spherical concave mirror produces an inverted an inverted real image: if object position (Xo) is greater than twice the focal length (f). The object is beyond the center of curvature (C).

If object is placed between the center of curvature and the focal point. Image is real and inverted but greater than the size of the object.

Summing up: Concave mirror can enlarge or reduce image, depending on where the object is placed in relation to the focal point.

Spherical Aberration: Defects of Concave mirrors

• Light rays do not converge at a focal point: makes image looks fuzzy

Spherical Aberration: Defects of Concave mirrors

• Solving the problem: reduce the ratio of the mirror’s diameter to its radius of curvature.

Virtual image

How can you determine whether the object is virtual or not? - Virtual image will appear to be located behind the mirror surface

Convex Mirror

• An outwardly curving reflective surface with edges that curve away from the surface.

Concave vs. ConvexImage produced

position cause

Concave Real inverted Object’s position is greater than the focal length

virtual upright Object’s position is less than the focal length

Convex virtual Upright and smaller

• Convex mirrors form smaller images making them appear farther away and produce wider field of view.

• Practical uses: security mirror, passenger side-rearview mirror to decrease the driver’s blind spot

• Mirrors can be used in combination to produce images of any size, orientation, and location desired. (Example: Telescope)

• A magnifying glass is a convex lens that is used to produce a magnified image of an object.

• A sheet magnifier consists of many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner. This arrangement is known as a Fresnel lens.

Mirror comparison

• Virtual images are always behind the mirror, so it’s image position is always (-)

• Negative magnification means inverted image.