MIRRORS

Light is form of energy that you can see! Every day, light waves reflect on objects and
into your eyes, which allows you to see the objects. Light also helps you identify objects
both near and far.
Reflection of Light in Mirrors

The laws of reflection state that:

1. the incident ray, the reflected ray, and the normal line to the reflecting surface all
lie in the same plane; and
2. the angle of incidence is equal to the angle of reflection.

mirror

Reflection in Plane Mirror

When light hits an object, every part of that object reflects light in all direction.
Some of the reflected light reaches our eyes. Thus, we can see an object.
Characteristics of images formed
by a plane mirror:
1.
Image is virtual;

2.
Same size as the object;
3.
Same orientation as the object; and

Reflection in a plane
Mirror
 4.
Same distance from the mirror as the
object.

Types of Reflection of Light

b. Diffused/Irregular Reflection. It is produced by rough surfaces

that tend to reflect light in all directions.
a. Specular/Regular reflection. It is defined as light reflected from a smooth surface at
a definite angle.

A B

(a) Mountains and its reflection on calm water (b) Mountains and its reflection on wavy water

The phenomenon by which a ray of light changes the direction of propagation when it
strikes a boundary between different media through which it cannot pass is described as the
reflection of light.

If the bundle of light rays is incident upon a smooth surface, then the light rays reflect
and remain concentrated in a bundle upon leaving the surface. On the other hand, if the
surface is microscopically rough, the light rays will reflect and diffuse in many different
directions.

Specular Reflection Diffuse Reflection

(smooth surface) (rough surface)
(a) (b)
Figure 5. (a) Parallel light rays reflect in one direction. (b) Parallel light rays reflect in different
directions.

Mirror Left-Right Reversal

If you view an image of yourself in a plane mirror (perhaps a bathroom mirror), you will
quickly notice that there is an apparent left-right reversal of the image. That is, if you raise
your left hand, you will notice that the image raises what would seem to be its right hand. If
you raise your right hand, the image raises what would seem to be its left hand. This is often
termed left-right reversal.

Figure 6. Mirror Left-Right Reversal

The letters in front of the ambulance are written laterally. This is because when seen in
rear view mirror by another vehicle, the image of the word would get inverted, letting the
driver read the word properly so that he can provide way to the ambulance.

Figure 7. Mirror Left-Right Reversal

Reflection on Spherical Mirrors

Most curved mirrors are called spherical mirrors because their shape follows the
surface of a sphere.

Two Kinds of Spherical Mirrors:

1. The Concave Mirror
• It reflects light inward to one focal point. It is used to
focus light.
• Also known as converging mirror has a reflecting
surface that is recessed inward (away from the Parallel rays incident
light).
converge after reflection on a

2. The Convex Mirror

• Also known diverging mirror is a curved mirror in which the reflective surface
bulges towards the light source.

light.
• Convex mirrors reflect light outwards; therefore they are not used to focus
There are two types of images formed by reflecting surfaces .

Figure 11. Reflection from Concave and Convex Mirror

Real Image Virtual Image

1. A real image is formed when light 1. A virtual image is formed when light
rays actually meet after reflection. rays do not actually intersect after
2. A real image can be formed on a reflection, but they appear to diverge
screen. from the mirror.
3. A real image is inverted with respect 2. A virtual image cannot be formed on
to the object. a screen.
e.g. The image of a distance object formed 3. A virtual image is erect with respect
by a concave mirror. to the object.
e.g. The image of an object formed by a
convex mirror.

Ray Diagram and Image Formation by Plane Mirror

A plane mirror makes an image of objects in front of the mirror; the image appears to
be behind the plane in which the mirror lies. An image is formed by reflection when two or

Image Formation by Plane Mirror

Location Behind the mirror

Orientation Upright
Size Same size as the object

Type Virtual
more reflected rays of a point meet at a single point. The image is formed at the point of
intersection of the reflected rays.

Images Formed by Curved Mirrors

In locating the image formed in curved mirror graphically, six important points are
considered. The following important points are enumerated below.

• Center of Curvature, – the center of the

sphere whose surface forms the curved
mirror
• Focal Point, – where the light rays meet

• Vertex, – the point where the principal axis

meets the mirror
4 + RZ GRHVW KHDQJO HRILQFLGHQFHFRP SDUHZ LW KW
KHDQJO HRI
• Principal Axis – the straight
UHIOHFW LRQ" line passing
through the center of curvature to the mirror
• Focal Length, 4 $SHU
– theLVFRSHL VDQLQVW
distance UXP HQW
fromIRUREVHU
the YDW LRQRYHUDURXQGRUWKURXJK focal
DQREVW DFO H( [ SO
DLQKRZ OLJKWW
UDYHOVLQDSHULVFRSH' LDJUDP WKH
point to the vertex O LJKW UD\ VDVW KHVHSDVVW KURXJKWKHSHULVFRSH
• Radius of Curvature, – the distance
Curved Mirrors
from the vertex ,QWKHDFW
to LYLthe
W\ \ RXIRXQ GRXW
center WKDW
ofW
KHDQ
theJOHRILQFLGHQFH ԦL LVHTXDO
WR curvature
W
KHDQJO
HRIUHIO
HFW
LRQ ԦU

,QV\ P ERO
V
Since the focal point is the midpoint of the line segment adjoining the vertex and the
Ԧ ԦU
center of curvature, the focal length would Lbe one-half the radius of curvature
7KLVLVRQHRIW
KHO
DZ VRIUHIO
HFW
LRQ7KHRW
KHUO
DZ VW
DWHVW
KDW

³ 7KHQRUP DO
OLQHLQFLGHQW
UD\ DQGW
KHUHIO
HFW
HGUD\ O
LHRQW
KHVDP H
SO
DQH´

5 HIO
HFWLRQRIO
LJKW
LVHP SO
R\ HGVLJQLILFDQW
O\ LQP DNLQJRSWLFDOLQVW
UXP HQWVOLNH
SHULVFRSHV3 HULVFRSHVDOO
RZ VHDQDYLJDWRUVLQDVXEP DULQHW RVHHW KHVXUIDFHRIWKH
Z DW
HU

7U\ W
KHQH[ W
DFW
LYLW
\WRIXUW
KHULQYHVW
LJDW
HWKHUHIO
HFW
LRQRIO
LJKW
LQSO
DQHP LUURUV

$ FW
LYLW
\

0 LUURU/ HIW5 LJKW

5 HYHUVDO

2 EM
HFW
LYHV
‡ ' HVFULEHWKHLP DJHVIRUP HGE\ SO
DQHP LUURU
‡ 6 KRZ DQXQGHUVW DQGLQJRIUHYHUVDOHIIHFWLQP LUURUVE\ Z ULW
LQJO
DWHUDO
O\
LQYHUW
HGOHWW
HUVDQGZ RUGV

0 DW
HULDOV
‡ DOSKDEHW
FKDUW
‡ SO
DQHP LUURU

3 URFHGXUH
ϭ͘ 3 O DFHWKHDO SKDEHW FKDUW
LQIURQWRIWKHSODQHP LUURU,GHQW
LI\ DO
OFDSLWDO
O
HW WHUVLQWKHDO SKDEHW W
KDWFDQEHUHDGSURSHUO \ LQIURQW
RIWKHP LUURU
Ϯ͘ : ULW HDWOHDVW Z RUGVDOO
LQFDSLWDOOHWWHUVW
KDWFDQEHUHDGSURSHUO \ ERWK
Z LWKDP LUURUDQGZ LWKRXWDP LUURULQIURQW
RILW