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Mirrors that are not flat are called
curved mirrors.
Depending on whether the reflective coating
is on the inside or outside of the curve will
decide if it is a concave or convex type of
mirror.
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If the mirror is coated on the inside of the
curve it is called a concave mirror.
Those which reflect from the outside of the
curve are called convex mirrors.
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A curved mirror is a cut out section of a circle.
In mathematics the distance from the curve to
the centre of the circle is referred to as a
radius (r).
For the purpose of curved mirrors, the centre of
the circle is called the centre of curvature (C).
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Any circle is an example of both a concave
and convex mirror. Note the solid line is the
reflected surface and the hatched side is the
back of the mirror.
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The principal axis is a line through the centre
of curvature that strikes the mirror at a
90o angle.
The vertex (V) of a curved mirror is where the
principal axis meets the mirror.
The centre of curvature and vertex both lie
along the principal axis.
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Half the distance between the centre of
curvature (C) and mirror is called the focus or
focal point (F).
Therefore, if the focus (F) has a distance of 4
cm from the curved mirror,
the centre of curvature(C) is 8 cm.
This is why the focus is given the symbol
of F and the centre of curvature is located at
2F.
1. _______
2. _______
5.
1.
2.
3.
3. _______
5.
4.
4.
3.
4. _______
2.
1.
5. _______
1.
2.
3.
4.
5.
Principal Axis
Vertex
Focal Point (F)
Centre of Curvature
Focal Length
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To determine the location of any image in a
concave mirror you need to draw at least two
incident rays.
The following rules will help you to draw the
incident and reflected rays for objects with a
concave mirror.
(i) A ray of light, which is parallel to the
principal axis of the concave mirror,
will reflect off of the mirror and pass through
the principal focus (F)
C
F
V
(ii) A ray of light passing through the centre of
curvature (C) of a concave mirror will
reflect back along the same path
C
F
V
(iii) A ray of light passing through the principal
focus (F) of a concave mirror will
reflect back parallel to the principal axis.
C
F
V
i) A ray of light, which is parallel to the principal
axis of a convex mirror will
reflect as if it had come from the principal
focus.
V
F
C
ii) A ray of light going towards the centre of
curvature(C) of a convex mirror is
reflected back along the same path.
V
F
C
iii) A ray of light going towards the principal
focus will reflect back parallel to the principal
axis.
V
F
C