# Chapter 17.1 Mirrors. Mirrors have been used for thousands of years. Polished metal was used to reflect The usage of today was made possible by Jean Foucault.

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Chapter 17.1 Mirrors

Mirrors have been used for thousands of years. Polished metal was used to reflect The usage of today was made possible by Jean Foucault –Developed a way to coat glass with silver

The Law of Reflection θ i = θ r The angle of incidence equals the angle of reflection The angles are always measured to the normal The normal is a line drawn perpendicular to the surface

Smooth and Rough Surfaces Specular reflection – parallel light rays are reflected parallel Shiny, mirrored surfaces

Diffuse reflection-the scattering of light off of a rough surface Light comes to surface parallel, but leaves non- parallel (scattered) Law of reflection stills applies Very little if any reflection

Objects & Plane-Mirror Images Plane mirror-a flat smooth surface that reflects light by specular reflection Object-the source of diverging light

The image is where the extended rays of the reflected rays seem to intersect The rays appear to come from the image but there really isn’t a source virtual image This is a virtual image

Virtual Image cannot be projected onto a screen Rays only appear to come from image

Properties of Plane Mirror Images Image distance, d i, is equal to object distance, d o Because image distance is behind the mirror the distance is negative d i = - d o Image height, h i, is equal to object height, h o Image is reversed

Concave Mirrors Example is the inside of a spoon “caves” inward The inner surface of a sphere There is a radius,r, the geometric center

Principal axis-the straight line perpendicular to the surface of the mirror at its center Focal point, F, is the point at which a distant object would be in focus The focal point is half the distance between the mirror and the center of curvature (radius), C

Focal length, f, is the distance from the focal point to the mirror

Real Vs Virtual Images Real image-ray actually converge and pass through the image Image can be seen on a screen Produced only by concave mirrors

All mirrors-plane mirrors, concave mirrors and convex mirrors produce virtual images Cannot be projected on screen Ray never actually converge

The Two Rays to Find an Image Ray 1-Incident light rays parallel to the principal axis of a mirror are reflected through the focal point

Ray 2-Incident rays that pass through the focal point are reflected parallel to the principal axis

Mathematical Method of Locating the Image Mirror Equation f is positive for concave mirrors and negative for convex mirrors

Magnification The ratio of the size of the image, h i, to the size of the object, h o, is called the magnification, m The magnification is related to the distances by the equation

If d i and d o are positive, then both m and h i are negative the image will be inverted

Virtual Images with Concave Mirrors The object must be between the focal point and the mirror Virtual, erect, and larger (only mirror that will give a larger virtual image)

Convex Mirrors A convex mirror reflects light from the outer surface The outside bottom of a spoon Rays from a convex mirror always diverge

Meaning image will always be virtual The focal length will always be negative The images are always reduced but the field of view is large Rearview mirrors and observation mirrors are examples

The Two Rays to Find an Image Ray 1-approaches the mirror parallel to the principal axis. The reflected ray is a dashed line from the focal point to the point where ray 1 strikes the mirror

Ray 2-approaches the mirror on a path that, if extended behind the mirror, would pass through F. The reflected ray 2 is parallel to the principal axis

The image is located at the apparent intersection of the rays behind the mirror, d i is negative

For all problems Find size Find type (real or virtual) Find position Find orientation (inverted or erect)

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