Optics: Mirrors and Lenses

23-2, 23-3

Plane Mirror Flat, smooth, regular reflection Image is reversed left to right or

front to back

Plane Mirrors object--source of diverging light

rays; luminous or illuminated image--point where extended rays

apparently intersect virtual image--no source is really

there; rays appear to diverge w/o doing so

real image--rays from object converge

Concave Mirrors reflects light from inner surface part of hollow a sphere Radius – r from geometric center of

sphere

Spherical Abberation Parallel rays converge at Focus (F)

only if close to principal axis Farther rays converge at a point

closer to mirror; therefore, image is a disk NOT a point (fuzzy image)

Spherical Abberation Parabolic mirrors have NO SA L used

to focus rays from distant stars to a sharp focus in telescopes

Hubble vs flashlights

Real vs Virtual Images Real images – light rays actually

converge and pass through the image. Can be projected onto paper or a screen

Virtual image – light rays diverge; cannot be projected or captured on paper/screen since rays DO NOT converge

Images from Concave Mirrors

Da Rules Rays parallel to Primary Axis reflect

through the Focus

Rays passing thru focus are reflected parallel to Primary Axis

Rays perpendicular to mirror are reflected back upon themselves and goes through the center of curvature.

Da Rules 2 Beyond C – if object farther from mirror than

C, then image is real, inverted and reduced

As object moves toward C then images move toward C and are real, inverted and reduced

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

If the object is inside C toward F then the image out beyond C, and is real, inverted, and enlarged

Convex Mirror Rules 3 As the object approaches F – the

image moves farther out If the object is at F – then all

reflected rays are parallel, image at ∞

Convex Mirror Rules 4 If object between F & mirror – then

no real image exists, virtual image behind mirror

Mirror and Lens Equation ho/hi = do/di

1/do + 1/di = 1/f

Magnification m = hi/ho = -di/do