Ch 18Ch 18

Mirrors and LensesMirrors and Lenses

Plane MirrorPlane Mirror flat, smooth surface flat, smooth surface

that reflects light in a that reflects light in a regular way; regular way;

it produces an image it produces an image that is virtual, erect, that is virtual, erect, and the same size as and the same size as the object; the object;

left and right appear left and right appear to be interchanged, to be interchanged, but front and back but front and back are interchangedare interchanged

Types of ImagesTypes of Images

Real imageReal image - source of converging - source of converging light rays; can be projected; are light rays; can be projected; are always invertedalways inverted

Virtual imageVirtual image - source of diverging - source of diverging light rays; cannot be projected; are light rays; cannot be projected; are always erectalways erect

Concave MirrorConcave Mirror

reflects light off its inner surfacereflects light off its inner surface Focal pointFocal point - (f) point on the principle axis - (f) point on the principle axis

where reflecting light converges; where reflecting light converges; f equals one-half the radius of curvature (C)f equals one-half the radius of curvature (C)

Spherical AberrationSpherical Aberration

defect of all spherical mirrors when the defect of all spherical mirrors when the parallel rays don’t all reflect through the parallel rays don’t all reflect through the focal point; focal point;

correct this by using a parabolic mirrorcorrect this by using a parabolic mirror

Concave Mirror Concave Mirror CharacteristicsCharacteristics

If the object is If the object is outside C, the outside C, the image is real, image is real, inverted, and inverted, and smallersmaller

Concave Mirror Concave Mirror CharacteristicsCharacteristics

If the object is at If the object is at C, the image is C, the image is real, inverted, and real, inverted, and the same sizethe same size

Concave Mirror Concave Mirror CharacteristicsCharacteristics

If the object is If the object is between C and f, between C and f, the image is real, the image is real, inverted, and inverted, and largerlarger

Concave Mirror Concave Mirror CharacteristicsCharacteristics

If the object is If the object is inside f, the image inside f, the image is virtual, erect, is virtual, erect, and largerand larger

Mirror EquationMirror Equation

11 = = 11 + + 11 or d or dii = = f x df x doo

f df do o d di i d doo – f – f f is the focal lengthf is the focal length ddoo is the object distance is the object distance ddii is the image distance is the image distance magnificationmagnification - the ratio of the image size - the ratio of the image size

(hi) to the object size (ho)(hi) to the object size (ho) m = m = hihi = - = - didi ho doho do

Mirror Equation RulesMirror Equation Rules

di is positive for real images, di is positive for real images, negative for virtual imagesnegative for virtual images

hi is positive for erect images, hi is positive for erect images, negative for inverted imagesnegative for inverted images

f is positive for concave mirrors, f is positive for concave mirrors, negative for convex mirrorsnegative for convex mirrors

Convex mirrorConvex mirror

reflects light off reflects light off the outer surfacethe outer surface

images are always images are always virtual, erect, and virtual, erect, and smallersmaller

these are used as these are used as safety mirrors safety mirrors because you get a because you get a wider angle of wider angle of visionvision

LensLens

transparent material with a transparent material with a refractive index larger than airrefractive index larger than air

The focal length of the lens depends The focal length of the lens depends on the shape and refractive index of on the shape and refractive index of the materialthe material

Convex LensConvex Lens

Convex lensConvex lens - (converging lens) - (converging lens) thicker in the middle than at the thicker in the middle than at the edges; acts like a concave mirror.edges; acts like a concave mirror.

Chromatic aberrationChromatic aberration - caused when - caused when light passes thru the edge of a lens; light passes thru the edge of a lens; the light is dispersed; correct using the light is dispersed; correct using an achromatic lensan achromatic lens

Convex Lens Convex Lens CharacteristicsCharacteristics

Outside 2f, image Outside 2f, image is real, inverted, is real, inverted, and smallerand smaller

Convex Lens Convex Lens CharacteristicsCharacteristics

At 2f, image is At 2f, image is real, inverted, and real, inverted, and same sizesame size

Convex Lens Convex Lens CharacteristicsCharacteristics

Between 2f and f, Between 2f and f, image is real, image is real, inverted, and inverted, and largerlarger

Convex Lens Convex Lens CharacteristicsCharacteristics

Inside f, image is Inside f, image is virtual, erect, and virtual, erect, and largerlarger

Concave lensConcave lens

(diverging lens) (diverging lens) thinner in the thinner in the middle than at the middle than at the edgesedges

acts like a convex acts like a convex mirror. mirror.

Always produces Always produces virtual, erect, and virtual, erect, and smaller imagesmaller image

Lens Equation RulesLens Equation Rules

The equation and rules stay the The equation and rules stay the same except f is positive for convex same except f is positive for convex lens and negative for concave lenslens and negative for concave lens

Corrective LensesCorrective Lenses

Near-Sighted PeopleNear-Sighted People

have too short a focal lengthhave too short a focal length correct this using a concave (diverging) correct this using a concave (diverging)

lenslens

Far-Sighted PeopleFar-Sighted People

have too long a focal length, have too long a focal length, correct this using a convex (converging) correct this using a convex (converging)

lenslens