The document discusses the reflection of light, including the laws of reflection and how images are formed using plane mirrors and curved mirrors. It explains that light rays reflect such that the angle of incidence equals the angle of reflection, and the image formed by a plane mirror is the same distance behind the mirror as the object is in front of it. It also describes characteristics of images formed by convex and concave mirrors depending on the position of the object.
7. Light Travels in Straight Lines
• A ray is the direction or path along which
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Previous light energy flows. In a diagram, rays are
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represented by lines with arrowheads.
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• A collection of rays is called a beam.
8. THE LAWS OF REFLECTION
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FIRST LAWS
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Next The incident ray, the reflected ray and
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the nornal all lie in the same plane
SECOND LAWS
The angle of incidence, I is equal to
the angle of reflection, r
9. THE LAWS OF REFLECTION
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When a ray of light strikes a plane
mirror, the light ray reflects off the
mirror. Reflection involves a change in
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direction of the light ray. The
convention used to express the
Next direction of a light ray is to indicate
the angle which the light ray makes
Help with a normal drawn to the surface of
the mirror. The angle of incidence is
the angle between this normal and the
incident ray; the angle of reflection is
the angle between this normal and the
reflected ray. According to the law of
reflection, the angle of incidence
equals the angle of reflection. These
concepts are illustrated in the
animation at the right.
10. Image Formation for Plane Mirrors
In the animation
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above, an object is
positioned in front
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of a plane mirror.
The plane mirror
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will produce an
image of the object
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on the opposite side
of the mirror. The
distance from the
onject to the mirror
equal the distance
from the image to
the mirror. Any
person viewing this
image must sight at
this image position.
11. Image Formation in Plane Mirrors
1. Draw the image of the
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Distance of the Distance of the object.
object image 2. Pick one extreme on
Previous the image of the
object and draw the
reflected ray which
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will travel to the eye
as it sights at this
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point
3. Draw the incident ray
object image for light traveling from
the corresponding
extreme on the object
to the mirror.
4. Repeat steps 2 and 3
normal for all other
Eye extremities on the
object.
Plane mirror
12. Check Your Understanding
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• Explain why emergency vehicles such as ambulances are
often marked on the front hood with reversed lettering
Previous (e.g., ECNALUBMA).
Answer: AMBULANCE
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Help • If Suzie stands 3 feet in front of a plane mirror, how far
from the person will her image be located?
Answer: 6 feet
• If a toddler crawls towards a mirror at a rate of 0.25 m/s,
then at what speed will the toddler and the toddler's
image approach each other?
Answer : 0.25 m/s
13. The image of an object in a plane mirror
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(a) Same size as object
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(b) Laterally inverted
(c) virtual
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(d) As far behind the mirror
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16. If a concave mirror is thought of as being
a slice of a sphere, then there would be a CURVED MIRROR
line passing through the center of the
sphere and attaching to the mirror in the
exact center of the mirror. This line is
Home known as the principal axis. The point
in the center of sphere from which the
mirror was sliced is known as the center
Previous of curvature and is denoted by the
letter C in the diagram below. The point
on the mirror's surface where the
Next principal axis meets the mirror is known
as the vertex and is denoted by the
letter A in the diagram below. The vertex
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is the geometric center of the mirror.
Midway between the vertex and the
center of curvature is a point known as
the focal point; the focal point is
denoted by the letter F in the diagram
below. The distance from the vertex to
the center of curvature is known as the
radius of curvature (abbreviated by
"R"). The radius of curvature is the radius
of the sphere from which the mirror was
cut. Finally, the distance from the mirror
to the focal point is known as the focal
length (abbreviated by "f"). Since the
focal point is the midpoint of the line
segment adjoining the vertex and the
center of curvature, the focal length
would be one-half the radius of curvature.
17. Ray diagrams of convex and concave mirror
Two rules of reflection for concave mirrors. They are:
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Any incident ray traveling parallel to the principal axis on the way to
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a concave mirror will pass through the focal point upon reflection.
Any incident ray passing through the focal point on the way to a
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concave mirror will travel parallel to the principal axis upon
reflection.
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The revised rules can be stated as follows:
Any incident ray traveling parallel to the principal axis on the way to
a convex mirror will reflect in a manner that its extension will pass
through the focal point.
Any incident ray traveling towards a convex mirror such that its
extension passes through the focal point will reflect and travel
parallel to the principal axis.
18. Concave mirror Convex mirror
F C
C F P
principal
axis
Any incident ray traveling
Any incident ray traveling parallel to the principal axis
parallel to the principal axis on the way to a convex
on the way to a concave mirror will reflect in a
mirror will pass through the manner that its extension will
focal point upon reflection. pass through the focal point.
19. Concave mirror Convex mirror
F C
P
C F
Any incident ray passing Any incident ray traveling
through the focal point on towards a convex mirror
the way to a concave mirror such that its extension
will travel parallel to the passes through the focal
principal axis upon point will reflect and travel
reflection. parallel to the principal axis.
20. Concave mirror Convex mirror
P
F C
C F
A line through the centre of A line through the centre of
curvature, C from the top curvature, C from the top
of the object of the object