Physics Note Chapter5

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Hoo Sze Yen

www.physicsrox.com

Physics SPM 2011

CHAPTER 5:
LIGHT AND VISION
5.1

Light Reflection

5.1.1 Plane mirrors

i

Incident ray

r

normal

Reflected ray

Law of light reflection:
• The reflected angle is always the same as the incident angle. • The incident ray, reflected ray, and normal line are in the same plane. Characteristics of an image formed by a plane mirror:
Size
Same
Direction
Upright, laterally inverted
Type
Virtual
Distance
Distance of an image from the plane mirror is the same as the distance of the object from the mirror
Image characteristics are commonly explained using the following three categories: Same
Image is exactly the same size as the object
Size
Magnified
Image appears bigger than the object
Diminished Image appears smaller than the object
Image appears to be in the same direction as the object
Direction Upright
Inverted
Image appears upside down compared to object
Real
Image formed is on the same side of the mirror as the object. Type
Real images mean you can capture the image on a screen.
Virtual
Image formed is on the opposite side of the mirror from the object Virtual images can only be seen; they cannot be captured on a screen.

Chapter 5: Light and Vision

Page 1 of 12

Hoo Sze Yen

www.physicsrox.com

Physics SPM 2011

5.1.2 Curved Mirrors
Common terminology of curved mirrors:
Centre of curvature, C
Pole of mirror, P
Principal axis
Radius of curvature, r (=CP)
Principal focus, F

Focal length, f
Aperture of mirror
Object distance, u
Image distance, v

The geometric centre of a hollow sphere of which the
concave or convex mirror is a part
The centre point on the curved mirror
A line which passes through the centre of curvature, C and
the pole of a curved mirror, P
Distance between the pole, P and the centre of curvature, C
A point through which all rays traveling parallel to the
principal axis converge to or appear to diverge from after
reflection by the mirror
The distance between the principal focus, F and the pole of
the curved mirror, P
The portion of the surface of the mirror that reflects light Distance of object from the pole of the mirror, P
Distance of image from the pole of the mirror, P

For both concave and convex mirrors, the focal length is half the radius; i.e. CF = FP. Concave mirror

Convex mirror

Rays traveling parallel to the principal axis Rays traveling parallel to the principal axis converge to a point, called the real principal appear to diverge from a point behind the focus, on the principal axis.

mirror which lies on the principal axis, called
the virtual principal axis.
Focal lengths are written in positive.
E.g. f = +20cm.

Chapter 5: Light and Vision

Focal lengths are written in negative.
E.g. f = -20cm.

Page 2 of 12

Hoo Sze Yen

www.physicsrox.com

Physics SPM 2011

Determining the Position and Characteristics of an Image with a Ray Diagram Concave mirror

A ray parallel to the
principal axis is reflected to
pass through F

A ray through F is reflected
parallel to the principal axis

A ray through C is reflected
back along its own path

Concave mirror

A ray parallel to the
principal axis is reflected as if
it came from F

A ray towards F is reflected
A ray towards C is reflected
parallel to the principal axis
back along its own path

To determine the position and characteristics of an image using a ray diagram: 1. Draw rays emanating from the top of the object to the mirror, and using the guide in the table above, draw their reflected paths. Use any of the two of the rays in the above guide. 2. A point on the image is produced at the intersection of two rays originating from the point on the object.

Chapter 5: Light and Vision

Page 3 of 12

Hoo Sze Yen

Position of object
O between F and P

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Physics SPM 2011

Images formed by a Concave Mirror
Ray diagram
Characteristics of...
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