CHAPTER – 10
LIGHT-REFLECTION
& REFRACTION
Light is a form of energy, which enable us to see the object.
In this chapter we will study the phenomena of reflection and refraction using the
property of light i.e. straight line propagation (Light wave travel from one point to
another, along a straight line).
Reflection of Light
When the light is allowed to fall on highly polished surface, such as mirror, most of
the light gets reflected. normal
Laws of Reflection
1. The angle of incidence is always equal to
Reflected
angle of reflection. ray
Incident
— i=— r ray
i r
2. The incident ray, reflected ray and the
normal to the reflecting surface at the
point of incidence lie in the same plane.
Points of incidences
Image formed by Plane Mirror (Plane reflecting surface)
Plane Mirror
A A1
Object Image
—
i
B —r B1
1) Virtual (imaginary) & Erect (Virtual The image that do not form on
screen.)
2) Laterally inverted (The left side of object appear on right side of image)
3) The size of image is equal to that of object
96 X-Science
,4. The image formed is as for behind the mirror as the object is in front of it.
Reflection of light by spherical Mirrors
Mirrors, whose reflecting surface are curved inward or outward spherically are
called spherical mirror.
For example - Spoon } fi
The curved surface of shinning spoon can be considered
as curved mirror.
If it is curved inward fi
Act as concave mirror
If it is curved outward fi
Act as a convex mirror.
Reflecting Reflecting
side side
Concave Convex
Mirror mirror
OR CONVERGING OR DIVERGING
MIRROR MIRROR
Few Basic terms related to Spherical Mirror
Radius of curvature
Principal R Concave
P
Axis C F f Mirror
focal length
Radius of curvature
Principal R
Axis P f F C
focal length
Convex
Mirror
97 X-Science
, 1. Principal axis : Line joining the pole and centre of curvature of the spherical
mirror.
2. Pole : The geometrical central point of the reflecting spherical surface.
(aperture), denoted by (P).
3. Aperture : The width of reflecting spherical surface.
4. Centre of curvature : The reflecting surface of a spherical mirror form a part
of sphere. It has a centre, which is known as centre of curvature, denoted by
(C)
5. Radius of curvature : The separation between the pole and the centre of
curvature. ie. PC = R
6. Focus point : The point on the principal axis, where all parallel rays meet
after reflection, denoted by (F)
7. Focal length : The length between the pole and focus point i.e. PF = f
8. Relationship between focal length and Radius of curvature.
F= R
2
Image formation by spherical Mirror
Before we learn the formation of image or ray diagram, let us go through few tips
a) Remember, A say of light which is parallel to principle axis always pass
through focus (meet at focus) or vice-versa
P P
Principal C F Principal C F
Axis Axis CONCAVE
CONCAVE MIRROR
MIRROR
Principal P F C
Axis
CONVEX MIRROR
Appear as if coming
from focus pt in case of convex mirror
98 X-Science
LIGHT-REFLECTION
& REFRACTION
Light is a form of energy, which enable us to see the object.
In this chapter we will study the phenomena of reflection and refraction using the
property of light i.e. straight line propagation (Light wave travel from one point to
another, along a straight line).
Reflection of Light
When the light is allowed to fall on highly polished surface, such as mirror, most of
the light gets reflected. normal
Laws of Reflection
1. The angle of incidence is always equal to
Reflected
angle of reflection. ray
Incident
— i=— r ray
i r
2. The incident ray, reflected ray and the
normal to the reflecting surface at the
point of incidence lie in the same plane.
Points of incidences
Image formed by Plane Mirror (Plane reflecting surface)
Plane Mirror
A A1
Object Image
—
i
B —r B1
1) Virtual (imaginary) & Erect (Virtual The image that do not form on
screen.)
2) Laterally inverted (The left side of object appear on right side of image)
3) The size of image is equal to that of object
96 X-Science
,4. The image formed is as for behind the mirror as the object is in front of it.
Reflection of light by spherical Mirrors
Mirrors, whose reflecting surface are curved inward or outward spherically are
called spherical mirror.
For example - Spoon } fi
The curved surface of shinning spoon can be considered
as curved mirror.
If it is curved inward fi
Act as concave mirror
If it is curved outward fi
Act as a convex mirror.
Reflecting Reflecting
side side
Concave Convex
Mirror mirror
OR CONVERGING OR DIVERGING
MIRROR MIRROR
Few Basic terms related to Spherical Mirror
Radius of curvature
Principal R Concave
P
Axis C F f Mirror
focal length
Radius of curvature
Principal R
Axis P f F C
focal length
Convex
Mirror
97 X-Science
, 1. Principal axis : Line joining the pole and centre of curvature of the spherical
mirror.
2. Pole : The geometrical central point of the reflecting spherical surface.
(aperture), denoted by (P).
3. Aperture : The width of reflecting spherical surface.
4. Centre of curvature : The reflecting surface of a spherical mirror form a part
of sphere. It has a centre, which is known as centre of curvature, denoted by
(C)
5. Radius of curvature : The separation between the pole and the centre of
curvature. ie. PC = R
6. Focus point : The point on the principal axis, where all parallel rays meet
after reflection, denoted by (F)
7. Focal length : The length between the pole and focus point i.e. PF = f
8. Relationship between focal length and Radius of curvature.
F= R
2
Image formation by spherical Mirror
Before we learn the formation of image or ray diagram, let us go through few tips
a) Remember, A say of light which is parallel to principle axis always pass
through focus (meet at focus) or vice-versa
P P
Principal C F Principal C F
Axis Axis CONCAVE
CONCAVE MIRROR
MIRROR
Principal P F C
Axis
CONVEX MIRROR
Appear as if coming
from focus pt in case of convex mirror
98 X-Science
