Physics 212 and 222
Reflection and Mirrors
What do we see?
Law of Reflection
Properties of Spherical Mirrors
Ray Tracing
I
Images
and
d the
th Equations
E
ti
1
Physics 212 and 222
Reflection
Magnetic
and Mirrors
Forces
TOC
2
1
Physics 212 and 222
Reflection
Magnetic
and Mirrors
Forces
TOC
θ
θ
Law of Reflection
θ=θ
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Physics 212 and 222
Reflection
Magnetic
and Mirrors
Forces
TOC
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2
Physics 212 and 222
Reflection
Magnetic
and Mirrors
Forces
TOC
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Physics 212 and 222
Reflection and Mirrors
For all reflected light rays, the angle of incidence θ is equal
to the angle of reflection θ’.
The eye sees the point from which the light originated as
though it were in a straight line from the angle of the
reflected ray.
The eye will not see the reflection of any point on the object
unless one of the rays originating from that object strikes the
mirror and reflects into the eye.
The eye will not see any part of an object for which all rays
approaching the eye hits the back of the mirror.
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Physics 212 and 222
Reflection and Mirrors
The law of reflection states that:
The incident ray, the reflected ray and the normal to the mirror
all lie in the same plane.
The angle of reflection equals the angle of incidence.
θ
θ
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Physics 212 and 222
Reflection and Mirrors
The law of reflection states that:
The incident ray, the reflected ray and the normal to the mirror
all lie in the same plane.
The angle of reflection equals the angle of incidence.
θ
θ
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Physics 212 and 222
Reflection and Mirrors
For a spherical mirror, rays that start at the center point will go
back through the center point.
This is because the normal to any
yp
point on the spherical
p
surface of the mirror points to the center of the sphere.
C
r
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Physics 212 and 222
Reflection and Mirrors
The principal axis is any line which crosses through the center
point of the mirror and touches the mirror itself.
The most commonly used axis is the one that bisects the
mirror.
C
10
5
Physics 212 and 222
Reflection and Mirrors
For any mirror, the focal point is defined as the point where
parallel rays that are near to the principal axis reflect to a point.
Any
y rays
y that originate
g
at the focal p
point will reflect parallel
p
to
the principal axis.
C
F
f
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Physics 212 and 222
Reflection and Mirrors
There are two types of spherical mirrors: concave (converging)
and convex (diverging).
Parallel rays reflecting off a convex mirror do not reflect to a
point. Instead they diverge in such a way as to appear to be
coming from the focal point.
F
C
12
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Physics 212 and 222
Reflection and Mirrors
Although any ray may be traced to find out where an image
point is, there are three principal rays that make the job easier.
1. Parallel Ray: Comes in parallel to the principal axis and goes out
through the focal point.
2. Focal Ray: Comes in through the focal point and goes out parallel
to the principal axis.
3. Radial Ray: Comes in through the center point and retraces its
path.
C
F
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Physics 212 and 222
Reflection and Mirrors
Although any ray may be traced to find out where an image
points is, there are three principal rays that make the job easier.
1. Parallel Ray: Comes in parallel to the principal axis and goes out as
though it came from the focal point.
2. Focal Ray: Comes in toward the focal point and goes out parallel to
the principal axis.
3. Radial Ray: Comes in toward the center point and retraces its path.
F
C
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Physics 212 and 222
Reflection and Mirrors
Images are real if all of the light rays pass through them.
them
Otherwise they are virtual.
Real images are inverted, virtual images are upright.
For mirrors, real images are found on the same side of the
mirror as the object. Virtual images are not.
Images may be smaller or larger than the object.
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Physics 212 and 222
Reflection
Magnetic
and Mirrors
Forces
TOC
C
F
f, do , ho and di are all
positive and hi is negative.
F
C
f and di are negative
g
and do, ho
and hi are positive.
Focal length (f), object distance (do) and image distance (di)
switch signs as you move across the mirror.
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Heights (ho for object and hi for image) are positive if the image
or object is upright and negative if they are inverted.
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Physics 212 and 222
Reflection and Mirrors
The same equation may be used to find the image distance,
object distance or focal length for both types of spherical
mirrors. This is called the mirror equation.
1 1 1
= +
f d o di
The magnification equation may be used to find the height of
the image or object or to find the magnification of a mirror.
m=
hi
d
=− i
ho
do
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Physics 212 and 222
Reflection and Mirrors
What do we see?
Law of Reflection
Properties of Spherical Mirrors
Ray Tracing
I
Images
and
d the
th Equations
E
ti
18
9