Reflection & Reflection & MirrorsMirrors

ReflectionReflection The turning back of The turning back of

an electromagnetic an electromagnetic wave (light ray) at wave (light ray) at the surface of a the surface of a substance.substance.

Depending on how Depending on how smooth the smooth the reflecting surface reflecting surface is, the reflection is, the reflection will either bewill either be diffuse diffuse oror specularspecular..

Reflections off flat Reflections off flat surfaces follow 2 surfaces follow 2 simple rules:simple rules:

angle in angle in ((incidenceincidence) ) equals angle outequals angle out ((reflectionreflection))

angles measured angles measured from the surfacefrom the surface ((normalnormal))

ReflectionReflection

Using the basic rules of reflection, Using the basic rules of reflection, we can createwe can create virtual imagesvirtual images..

Virtual images are images formed Virtual images are images formed by light rays that appear to by light rays that appear to intersect.intersect.

ex. Looking in a mirrorex. Looking in a mirror

Image location can be predicted Image location can be predicted withwith “ray diagrams”.“ray diagrams”.

ReflectionReflection

ReflectionReflection

Ray diagram of mirror image (full Ray diagram of mirror image (full length mirror)length mirror)

Two types of curved Two types of curved mirrorsmirrors

1.1. Concave mirrorsConcave mirrors – inwardly – inwardly curved inner surface that curved inner surface that converges incoming light rays. converges incoming light rays.

2.2. Convex MirrorsConvex Mirrors – outwardly – outwardly curved, mirrored surface that curved, mirrored surface that diverged incoming light rays. diverged incoming light rays.

Image location can be predicted Image location can be predicted with mirror equations.with mirror equations.

Curved MirrorsCurved Mirrors

Principal axis

Center of Curvature ( C )

Focal Length ( f )

Object distance ( p )

h

1/object distance + 1/image distance = 1/object distance + 1/image distance = 1/focal length1/focal length

1/p + 1/q = 1/1/p + 1/q = 1/ff

Curved MirrorsCurved Mirrors

Alternate Mirror Equation:Alternate Mirror Equation:

1/p + 1/q = 2/R1/p + 1/q = 2/R

1/object distance + 1/image distance = 2/radius of 1/object distance + 1/image distance = 2/radius of curvaturecurvature

Concave mirrors…Concave mirrors…

can form BOTH can form BOTH virtualvirtual and and realreal images of an object depending images of an object depending on how far the object is placed on how far the object is placed away from the mirror.away from the mirror.

Real image: Real image: an image formed an image formed when light rays intersect at a when light rays intersect at a single point.single point.

Images produced by concave mirrors Images produced by concave mirrors (virtual or real) will NOT be the (virtual or real) will NOT be the same size of our object.same size of our object.

They will be magnified (M)They will be magnified (M)

magnification = magnification = image heightimage height = - = - image image distancedistance

object height object object height object distancedistance

M = h'/h = - q/pM = h'/h = - q/p

+ M = upright and virtual image+ M = upright and virtual image- M = inverted and real image- M = inverted and real image

Concave mirrorsConcave mirrors

Rules for drawing Rules for drawing reference linesreference lines

Ray Line from object Line from mirror to Ray Line from object Line from mirror to

to mirror to mirror reflected imagereflected image

1. Parallel to principal Through focal point 1. Parallel to principal Through focal point axis Faxis F

2. Through focal point parallel to principal 2. Through focal point parallel to principal

F axisF axis

3. Through the center back along itself 3. Through the center back along itself through through

of curvature C Cof curvature C C

Object distance is greater Object distance is greater than the focal lengththan the focal length

Principal axis

Reflecting Surface

Ray DiagramRay Diagram

fC

Object distance is less than Object distance is less than the focal lengththe focal length

Principal axis

Reflecting Surface

Ray DiagramRay Diagram

fC

Convex MirrorsConvex Mirrors

Focal point and center of Focal point and center of curvature are located behind the curvature are located behind the mirror’s surface.mirror’s surface.

M is always +, but less than 1M is always +, but less than 1

Image is always virtualImage is always virtual

Provide a large field of viewProvide a large field of view

Convex MirrorsConvex Mirrors

Principal axis

f C

Reflecting Surface