Upload
caren-norris
View
216
Download
2
Tags:
Embed Size (px)
Citation preview
Image of a point
do di
A’A
Due to the similarity of the triangles on the diagram, all the reflected rays extend backward to one point.
No matter where the observer is, the image is always:
•Behind the mirror
•On the perpendicular line drawn from the object, A.
•At the same distance from the mirror as object.
Image Formation in Plane Mirrorsby a Point Source of Light
dodi
A 1 A’
To construct the image of a point, -sketch a line perpendicular to the mirror through A- measure do (from A to the mirror surface)
- construct image A' on the other side such as do= di
Because all the reflected light rays intersect at one point anyway, there is no need to construct many of them, but only one: the perpendicular to the surface of the mirror.
Image Formation in Plane Mirrors
To construct the image of an object, there is no need to construct an image of each single point of it.
Construct an image of the extreme points (e.g. top and the bottom), then connect these edge points
Properties of Images Formed by Plane Mirrors
S
A
L
T
ttitude
ize
ocation
ype
The image has the same size as the object (no magnification)
The image is up-right but Laterally Inverted (Left / Right)
Image is at the same distance from mirror as the object
(see the next slide first)
Type of the images formed by plane mirrors
Our eye catches diverging rays reflected from mirror.
Observer has a sensation that image is at the intersection of the light rays extended behind the mirror. There is nothing behind the mirror.
Light only appears to us to come from this point.This image is imaginary, or virtual image because there is no real light rays going to or coming from behind the mirror.
Properties of Images Formed by Plane Mirrors
S
A
L
T
ttitude
ize
ocation
ype
The image has the same size as the object (no magnification)
The image is up-right but Laterally Inverted (Left / Right)
Image is at the same distance from mirror as the object
Plane mirrors form virtual images
8
Concave
Concave MirrorsConcave Mirrors
•have the reflecting surface inside of the curve
•AKA Converging mirrors as parallel to the axis rays are reflected inward
9
Concave Mirror Terminology
Principal axis: line connecting the centre of curvature with the mirror’s vertex
Is the centre of the sphere the mirror is cut from. The length of C is the radius of the sphere
Focal Point (focus) : where all parallel to the axis incident rays meet after reflection in the mirror.
Vertex: centre of the mirror, located on axis
Concave Mirror: a mirror with reflecting surface curved inward Focal
distance from F to V
11
Image Formation using Ray Diagrams for a Concave Mirror: Principal Rays Summary
Incident Ray Reflected Ray
Parallel to principal Axis Through the focal point
Through the focal point Parallel to principal Axis
Through C Through C
On the vertex of the mirror Such as angle with axis is same for incident and reflected ray
How do we see the image
A point object emit (or reflect) light in all directions
13
All the rays reflected by mirror meet at one point
Eye detects light coming out of that point
Brain identifies this point as the image
Ray Diagrams for a Non-Point Source
14
For non-point objects, construct images of few extreme point.
O
O’
For perpendicular to the axis objects, locate the image of the top,
Connect with axis at right angle to locate the bottom of the image
Any point on axis will form image on axis.
Practice
Practice constructing ray diagrams for 5 different locations of the object
Note that the properties of these images will be quite different.
15
16
Object is Located beyond the Centre of Curvature
S: smaller A: inverted L: between F and C T: real
17
Object is located at the Centre of Curvature
Think of mirror as almost flat close to axis to avoid spherical aberration
Image Properties: S: same as obect A: Inverted L: at C T: real
This image is very convenient in determining the mirror’s focal length
19
Object is located at Focal Point
S: N/AA: N/AL: N/AT: N/A
Light rays are parallel, they never meet.No image formed: no properties
20
Object in between Focal point and Mirror
Size: Enlarged Attitude: Up-right Location: Behind the mirror Type: Virtual
F C
This time, converging mirror actually converges the light rays.
Demo reminder: large mirror
21
Concave Mirror Image Properties Summary
Object location
Size Attitude Location Type
do > c smaller inverted f < di< c Real
do= c same inverted di= c Real
f < do< c bigger inverted di > c Real
do= f N/A N/A N/A N/A
do< f bigger up-right Anywhere behind the mirror
Virtual