# Chapter 18 1 Mirrors Plane Mirror a flat

• Slides: 17

Chapter 18 -1 Mirrors

Plane Mirror • a flat, smooth surface • light is reflected by regular reflection rather than by diffuse reflection • Light rays are reflected with equal angles of incidence and reflection.

Plane Mirror • Produces a virtual image which appears to be an equal distance behind the mirror. With a virtual image, the light rays do not actually converge on the point where the image appears. • The object and the image have the same size. • They are pointing in the same direction, so the image is an erect image. • Left and right are reversed which is to say “the front and back of the image are reversed. ”

Concave Mirrors • A concave mirror reflects light from its inner, (“caved in”) surface. • The principle axis is the straight line perpendicular to the surface of the mirror at its center. The focal point • is the point where all rays parallel to the principal axis meet. • It is half the distance between the mirror and the center of curvature (C). • If you point the principal axis of a concave mirror at the sun, all the rays (which are parallel to each other—at “infinity”) will be reflected through the focus • The distance from the focal point to the mirror along the principal axis is the focal length, f, of the mirror.

Real vs Virtual Images Real Image: • the rays actually converge and pass through the image • it can be seen on a piece of paper Virtual Image: • The rays do not converge at the location of the virtual image • The virtual image cannot be projected on a screen

How to draw Ray Diagrams: • Draw the mirror, principal axis, a vertical line where the principal axis touches the mirror, the image, the focal point (F) and the center of curvature (C). Ray 1 (the parallel ray) is from the object to the mirror parallel to the principal axis. The reflected ray goes through the focal point Ray 2 (the focus ray) is from the object through the focal point. The reflected ray is parallel to the principal axis Where Ray 1 and Ray 2 intersect is the location of the image.

Possible scenarios for Concave Mirrors Object Image

Lens/mirror equation: “If I do I die. ” • f = focal length • do = distance of object from mirror • di = distance of image from mirror

Magnification • the ratio of the size of the image, hi , to the size of the object, ho or

b. How high is the image?

Virtual Images Formed by Concave Mirrors

Image defect in Concave Mirrors Spherical aberration • Parallel Incident Light from outer edge of spherical mirror fails to focus at a point • Fix: Parabolic mirror

Convex Mirrors • A convex mirror is a spherical mirror that reflects light from its outer surface. • Rays reflected from a convex mirror always diverge. • Focal length, f, is a negative number (because F is behind the mirror) • di is negative because the image is behind the mirror • Convex mirrors do not form real images. • Images are reduced in size and so appear far away • “Fisheye lens” the image is small (reduced) but wide ranging (enlarged) field of view; upright image, virtual, reduced (images seem farther away) • Good for security mirrors & rearview mirrors in cars

Problem from Opening Page of Chap 18 in Textbook • Four Butterflies but only one is real. • Identify the images and the shape of lenses that produced them:

End 18 -1