Reflection

• Regular reflection occurs when parallel light rays strike a smooth surface and reflect in the same direction.

• Diffuse reflection occurs when light rays reflect off a rough surface and are scattered in different directions.

Reflection• The Law of Reflection: When light reflects

off a surface, the angle of incidence is always equal to the angle of reflection.

• Where are plane mirrors used?

Plane mirrorsA virtual image is any image formed by rays that do not actually pass through the location of the image. Light rays are not coming from where the image appears to be.

Curved Mirrors• Concave and convex

• Curved mirrors obey the law of reflection.

Curved mirror definitions• All reflected rays eventually meet at a common point. The point

where light rays meet, or appear to meet, is called the focal point, F.• The middle of a curved mirror is the vertex. The principal axis is an

imaginary line draw through the vertex. • The distance from the vertex to the focal point is the focal length, f. • The center of curvature, C, is the center of the circle that would be

formed if you extended the curve of the mirror.

The focal point is exactly between the center of curvature and the vertex.

Finding the image

Each time you find the image, you must determine the following:

•Size: Is it smaller, bigger, or the same size as the object?

•Attitude: Is it upright or inverted?

•Location: Is it behind or in front of the mirror?

•Type: Is it real of virtual?

Real vs. Virtual• A real image is formed by light rays that converge at the location of

the image. • If the object is farther away from the mirror than the focal point, the

reflected rays form a real image.• A real image can be projected onto a screen: If you place a piece of

paper at the spot where a real image forms, a focused image will appear on the piece of paper.

• A virtual image is any image formed by rays that do not actually pass through the location of the image.

• Light rays are not coming from where the image appears to be. • Unlike a real image, a virtual image cannot be projected onto a

screen.

Drawing a CONCAVE MIRROR ray diagramNote: Show real rays using solid lines and virtual rays using dashed-lines.

•Ray 1: parallel from a point on the object to the principal axis (Rays that are parallel to the principal axis will reflect through the focal point on a concave mirror.)

Ray 2: from a point on the object through the focal point. (Rays that pass through the focal point on a concave mirror will be reflected back parallel to the principal axis.)

Ray 3: Draw a line from the same point on the object through the center of curvature. When the ray hits the mirror, it will reflect back on itself. This line determines the quality of the mirror.

Draw the image where the rays intersect.

Size: Smaller

Attitude: Inverted

Location: In front

Type: Real

Complete the following tableLOCATION OF OBJECT SIZE OF IMAGE ATTITUDE OF

IMAGELOCATION OF

IMAGETYPE OF IMAGE

More than two focal lengths away from

mirror 

Smaller Inverted In front Real

Between one and two focal lengths away

from the mirror

       

Object is at the focal point

  

       

Object is between the mirror and the focal

point 

       

Magnification• One use of concave mirrors is magnification.• Magnification: How large or small an imagine is compared to with the object.

• If the image is bigger than the object, then the magnification will be greater than 1.• If the image is smaller than the object, then the magnification will be less than 1.

Convex mirrors• Instead of collecting light rays, a convex mirror spreads out

the rays.

Drawing a convex ray diagram:

Ray 1: from a point on the ray parallel to the principal axis (Any ray that is parallel to the principal axis will appear to have originated from the focal point.)

Ray 2: from a point on the object toward the focal point (Any ray that is directed at the focal point on a diverging mirror will be reflected back parallel to the principal axis.

Draw the virtual image where the rays appear to intersect.

WHAT ARE THE PROPERTIES OF THE IMAGE PRODUCED?

Mirror Equation• Rules:• Concave mirrors have positive focal length and convex

mirrors have negative focal length• Distances are positive if they are in front of the mirror,

and negative if they are behind the mirror.• All measurements are made along the principal axis from

the surface of the mirror.

Concave vs. Convex mirrors• Concave mirrors are designed to collect light and bring it

to a single point

• Examples: telescopes, flashlights, car headlights, cosmetic mirrors, dental examination lights

• Convex mirrors allow you to view a large region that you could not see with a plane mirror of the same size.

• Examples: Store security, parking lot safety, side-view mirrors, camera phones

References• Pearson Investigating Science 10• http://www.blueskiesandyellowdogs.com/2010/08/17/what-i-love-to-see-most-in-my-rear-view-mirror/• http://www.sayulitalife.com/dentalsayulita• http://www.math.ubc.ca/~cass/courses/m309-01a/chu/Fundamentals/reflection.htm• http://www.bnl.gov/slc/DiscoveryActivitiesSLC/MirrorMagic.asp• http://www.bnl.gov/bnlweb/schoolprograms.html• http://shiratdevorah.blogspot.ca/2010/10/rainbow-covenant.html• http://epod.usra.edu/blog/2010/03/highway-mirage.html