Curved Mirrors
and Ray Diagrams
SNC2D
Concave Mirrors
A concave mirror is a curved mirror with the
reflecting surface on the inside of the curve.
The point C is the centre of curvature and
the distance between C and the vertex A is
the radius of curvature, R.
Concave Mirrors
Halfway between C and A is F, the focal point
or principal focus.
The focal length, f = R/2.
The Focal Point
The focal point is the point at
which rays incident parallel to
the principal axis will meet
after reflection.
The Focal Point
The focal point is the point at
which rays incident parallel to
the principal axis will meet
after reflection.
(Recall the Law of Reflection.
In this case, the normal to the
mirror is the radius.)
Image Formation
Where and how is an image formed?
Image Formation
Where and how is an image formed?
Image Formation
Where and how is an image formed?
2 Rules of Reflection
To locate an image, we will use the 2 rules:
 A ray travelling parallel to the principal axis
will reflect through the focal point.
 A ray travelling through the focal point will
reflect parallel to the principal axis.
Ray Diagrams: Step 1
From the top of the object,
draw two rays towards the
mirror, one parallel to the
axis and one through the
focal point
Ray Diagrams: Step 2
Reflect these rays according
to the rules of reflection.
Ray Diagrams: Step 3
Mark the image of the top of the
object at the intersection of
the reflected rays.
Ray Diagrams: Step 4
The bottom of the image forms
on the principal axis. Draw
your complete image.
Image Characteristics
Note that the image of an object
beyond the centre of
curvature of the mirror is:
S:
A:
L:
T:
Image Characteristics
Note that the image of an object
beyond the centre of
curvature of the mirror is:
S: Smaller
A:
L:
T:
Image Characteristics
Note that the image of an object
beyond the centre of
curvature of the mirror is:
S: Smaller
A: Inverted
L:
T:
Image Characteristics
Note that the image of an object
beyond the centre of
curvature of the mirror is:
S: Smaller
A: Inverted
L: Between F and C
T:
Image Characteristics
Note that the image of an object
beyond the centre of
curvature of the mirror is:
S: Smaller
A: Inverted
L: Between F and C
T: Real
Image Characteristics
The characteristics of the image formed by
the mirror will change with the location of
the object.
Ref: Practice Sheet:
“Concave Mirrors and Ray Diagrams”
Concave Mirrors: Answers
The image formed by
an object beyond C is
S: smaller
A: inverted
L: between F and C
T: real
Concave Mirrors: Answers
The image formed by
an object at C is
S: the same size
A: inverted
L: at C
T: real
Concave Mirrors: Answers
The image formed by
an object between C
and F is
S: larger
A: inverted
L: beyond C
T: real
Concave Mirrors: Answers
There is no image
formed by an object
at F:
Concave Mirrors: Answers
The image formed by
an object between F
and the mirror is
S: larger
A: upright
L: behind the mirror
T: virtual
Concave Mirrors: Answers
The image formed by
an object between F
and the mirror is
S: larger
A: upright
L: behind the mirror
T: virtual
Convex Mirrors
A convex mirror is a curved
mirror with the reflecting
surface on the outside of the
curve.
The centre of curvature and
the focal point will be on the
far side of the mirror. The
focal length will be negative.
Convex Mirrors are Diverging
Light rays reflecting from
a convex mirror will
diverge, i.e. never
intersect.
Any image formed is
therefore always virtual.
Revised Rules of Reflection


A ray travelling parallel to the principal
axis will reflect such that the extension of
the reflected ray will pass through the
focal point.
A ray travelling towards the mirror such
that its extension will pass through the
focal point will reflect parallel to the
principal axis.
Ray Diagrams Again
Step 1:
Ray Diagrams Again
Step 2:
Ray Diagrams Again
Step 3:
Ray Diagrams Again
Step 4:
Ray Diagrams Again
Step 4:
The image is (S) smaller, (A) upright,
(L) behind the mirror, and (T) virtual.
More Practice

p. 427 #1 – 5 and p. 433 #15