Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

CHAPTER – 10

LIGHT-REFLECTION
& REFRACTION
Light is a form of energy, which enable us to see the object
...
e
...

Reflection of Light
When the light is allowed to fall on highly polished surface, such as mirror, most of
the light gets reflected
...


2
...

—
i=—
r
The incident ray, reflected ray and the
normal to the reflecting surface at the
point of incidence lie in the same plane
...
)

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

The image that do not form on

X-Science

4
...


Reflection of light by spherical Mirrors
Mirrors, whose reflecting surface are curved inward or outward spherically are
called spherical mirror
...

If it is curved inward fi
Act as concave mirror
If it is curved outward fi
Act as a convex mirror
...


Principal axis : Line joining the pole and centre of curvature of the spherical
mirror
...


Pole : The geometrical central point of the reflecting spherical surface
...


3
...


4
...
It has a centre, which is known as centre of curvature, denoted by
(C)

5
...
ie
...


Focus point : The point on the principal axis, where all parallel rays meet
after reflection, denoted by (F)

7
...
e
...


Relationship between focal length and Radius of curvature
...


i

C

P

—
i=—
r

r

F

—
i
—
r

99

—
i=—
r
F

C

X-Science

Note : A ray of light passes through centre of cus-valerie reflecting spherical
surface is always act as normal at the point of incidence
...
Image
formation by a concave mirror for different position of the object
1
...


Object
Beyond C

F

Size of
Image
Highly diminished
(point size)

A
object

B

B1

P

F

C image

—
i
—
r

Object
At C

A
B1 B

P
F

Position of
Image
Between F&C

Nature
Real and
Inverted

Size of
Image
Small

A1

3
...


Object
Between C&F

—
i=—
r
Position of
Nature
—
i
Image
P
Real and
—
r
Beyond C
Inverted

A
Object
B1

B

C

F

Image
A

5
...


Object
Between F&P
(Special Case)

A

C

F

P
—
i
r
B —

B1

Position of Image
Behind the mirror
Size of Image
Enlarged

Nature
Virtual
and
Erect

Image formation by Convex Mirror
1
...


Object
Anywhere between
infinity and pole
of the mirror

A
A1

P
B

B1

Position of Image
Between P & F

Size of Image
Very small

F

Nature
Virtual & erect

Uses of Concave Mirror
1
...


2
...


Used by dentist to see large images of the teeth

4
...


Uses of Convex Mirror
1
...
It also helps
the driver to view large area
...


The object is always placed to the left side of mirror
...


All distance should be measured from pole (P); parallel to principal axis
...


Take 'P' as origin
...


1
1
1
F = v + u
R
where f = 2

MAGNIFICATION
It is expressed as the ratio of the height of the image to height of the object
m=

height of image h1
=
height of object h

1

It is also related to 'u' and 'v'
–v
m= u
2
\
from 1 and 2 equation
1

m=

h
h

1
image height from principle axis
– v where h fi
1
= u
h fi
Object height from principle axis
...

A ray of light bends as it moves from one medium to another

103

X-Science

Refraction is due to change in the speed of light as it enters from one transparent
medium to another
...

normal

normal
Incident
Ray

Denser medium

Raver medium
Denser medium

Rarer medium

Refracted Ray

When ray travel from Rarer to Denser it bends When ray travel from denser to
towards normal after refraction
rarer medium it bends away
from normal
Some Commonly observed phenomenon due to Refraction
1
...


2
...


3
...


Refraction through a Rectangular Glass Slab
A

N

Incident ray

Air (Rarer Medium)

i1
K

L
O
r1
i2 N

N

He

c)

F2
Principal
Axis

O

F2

F1
O

Principal
Axis

A ray passes through optical centre 'O', paeses without any deviation
...


Object
At infinity

2F1

2
...


Object
At 2F1
A
1

B

B
2F1

F1

O

2F2

F2

A1

108

Position of Image
At 2F2
Size of Image
Same size of
object

Nature
Real &
inverted

X-Science

4
...


Object
At focus F1

Position of Image
at infinity

A

Size of Image
Highly Enlarged

B
2F1

6
...

Object
Alt infinity

2F1

Nature
Real &
inverted

O

F2

109

Nature
Virtual &
Erect

2F2

X-Science

2
...

m=

height of image
height of object

1

h
= 1
h

=

}

1

h – image height
from principal axis
h – object height
from principal axis

It is also related to 'u' & 'v'
m=

v
u

2

110

X-Science

From equation 1 & 2
m=

h1
h

v
u

=

If magnitude of m > | fi
Image is magnified
m = 1 fi
Image is of same size
m < | fi
Image is deminished
Few tips to remember sign convention for spherical lens
Object height h

fi
is always positive

Image height h1

Real fi
is always negative
Virtual fi
is always positive

Object distance from optical centre u fi
is always negative

}

Real fi
positive
Image distance from optical centre v fi
virtual fi
negative

}

Convex lens fi
is always positive
Focal length v fi
Concave lens fi
is always negative
Power of Lens
The degree of convergence or divergence of light ray achieved by a lens is known
as power of a lens
...


EXERCISE
(Question Bank)
Very Short Answers Type Questions (1 Mark)
1
...


What is the nature of image formed by concave mirror if the magnification
produced by the mirror is +3?

3
...


Find the focal length of a convex mirror, whose radius of curvature is 30 cm?

5
...


An object is held at the principal focus of a concave lens of focal length f
...


Show the angle of incidence and angle of refection
...


Complete the ray diagram
...


Define the SI unit of power of lens
...


When light undergoes refraction at the surface of seperation of two media,
what happens to speed of light
...


What do you understand by refraction of light
...


2
...
54 and the speed of light in air is 3x10 m/s
...


A convex mirror used on an automobile has a focal length of 6m
...
Find the nature and location of image
...


A concave lens of focal length 15cm, forms an image 10 cm from the lens
...


Two thin lens of power +3
...
5D are placed in contact
...

(p = + 10, f = 1m)

6
...
Define refractive index of a medium
...


2
...

a)

At infinity

b)

between F1 & 2F1

c)

At 2F1

d)

Beyond 2F1

e)

between F1 & optical centre 'O'

113

X-Science



---