Wavefronts and Rays In describing the propagation of light as a wave we need to understand wavefronts a surface passing through points of a wave that have the same phase and amplitude ID: 675433
Download Presentation The PPT/PDF document "Chapter 25: The Reflection of Light: Mir..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Chapter 25: The Reflection of Light: MirrorsSlide2
Wavefronts and Rays
In describing the
propagation of
light as a wave we need to understand:wavefronts: a surface passing through points of a wave that have the same phase and amplitude.rays: a ray describes the direction of wave propagation.A ray is a vector perpendicular to the wavefront.Slide3
Types of Reflection
Specular reflection-
when parallel light rays strike a smooth, plane surface, the reflected rays are parallel to each other. (mirrors do this)
Diffuse reflection – a rough surface reflects the light rays in all directionsSlide4
The Reflection of Light
Most objects reflect a certain portion of the light falling on them.
For a ray of light incident on a mirror
The angle of incidence, Ɵi , is the angle that the incident ray makes with respect to the normalThe normal is a line drawn perpendicular to the surface at the point of incidence.The angle of reflection,
Ɵ
r
,
is the angle that the reflected ray makes with the normal.Slide5
Law of Reflection
The incident ray, the reflected ray, and the normal to the surface all lie in the same plane, and the angle of reflection
Ɵ
r equals the angle of incidence ƟiƟr = ƟiSlide6
Check your Understanding
Consider the diagram
below.
Which angle (A, B, C, or D) is the angle of incidence? ______ Which angle is the angle of reflection? ______Slide7
Check your Understanding
A ray of light is incident towards a plane mirror at an angle of 30-degrees with the mirror surface. What will be the angle of reflection?Slide8
Plane Mirrors
When you look into a plane (flat) mirror, the image you see has 3 properties:
The image is upright
The image is the same size you areThe image is located as far behind the mirror as you are in front of it.The image is also reversed left to rightSlide9
Plane Mirrors
When you look into a plane (flat) mirror, the image you see has 3 properties:
The image is upright
The image is the same size you areThe image is located as far behind the mirror as you are in front of it.Slide10
Plane Mirrors
A mirror is an object that reflects light. A plane mirror is simply a
flat mirror
. Plane mirrors are ground to be flat – the flatter the more expensive. (Typically good ones have no hills or valleys larger than 500nm).Consider an object placed at point P in front of a plane mirror. An image will be formed at point P´ behind the mirror.Slide11
Plane Mirrors
d
o
= distance from object to mirrordi = distance from image to mirrorho = height of objecthi = height of imageFor a plane mirror: do
= d
i
and
ho = hi
d
o
d
i
h
o
h
iSlide12
Images
An image is formed at the point where the rays of
light leaving
the object either actually intersect or where they appear to originate.If the light rays actually do intersect, then the image is a real image. If the light only appears to be coming from a point, but is not physically there, then the image is a virtual image.Slide13
Images
The image is called virtual because it
does not
really exist behind the mirrorSlide14
Check Your Understanding
To save expenses, you would like to buy
the shortest
mirror that will allow you to see your entire body. Should the mirror be (a) half your height (b) two-thirds your height, or (c) equal to your height?Does the answer depend on how far away from the mirror you stand?Slide15
Assignment
Check Understanding: p 778 #1-3
Focus: p 792 #2, 4,
7Problems: p. 793 #3-6