Prove, in the case of a convex mirror, that 1 v - 1 u = 2 r = 1 f .

Let AB be an object lying on the principle axis of the convex mirror of small aperture. Virtual image is behind the mirror A'B'. Draw LN perpendicular to the principle axis. Now ∆ NLF and A'B'F are similar. Therefore, A ' B ' N L = A ' F N F Since aperture is small, point N lies very close to P. So, N F = P F , L N = A B Also, ∆ ABC and A'B'C are similar, so, A ' B ' A B = A ' C A C = P C - P A ' P A + P C So we get, P F - P A ' P F = P C - P A ' P A + P C . . . . . . ( i ) From diagram, P A ' = v P F = f P C = R = 2 f P A = u (without any sign convention) So, equation (i) becomes, f - v f = 2 f - v u + 2 f ⇒ 2 f 2 - v f = u f - u v + 2 f 2 - 2 v f ⇒ u v = u f - v f Dividing by u v f , we get, 1 f = 1 v - 1 u .

E M B I B E

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 8

MEDIUM

12th West Bengal Board

IMPORTANT

Earn 100

A man stands at the centre of a room. A plane mirror hangs on the wall in front of him. Show that the minimum height of the mirror through which the man can see the full image of the wall behind him is one-third the height of the wall.

Important Questions on Reflection of Light

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 9

Explain, with the help of a diagram, the action of periscopes. For what purpose is it used ?

MEDIUM

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 10

Prove, in the case of a convex mirror, that

\frac{1}{v} - \frac{1}{u} = \frac{2}{r} = \frac{1}{f}

.

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 11

Establish the relation connecting object distance, image distance and focal length of a spherical mirror. Show that the ratio of the length of the image formed by a concave mirror to the length of the object is equal to the ratio of their respective distances from the mirror.

MEDIUM

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 12

Explain with neat diagram the formation of image of an extended object by reflection from a convex mirror. Obtain a relation between the object distance, image distance and the focal length of the mirror.

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 13

How will you proceed to determine the focal length of a convex mirror ?

EASY

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 1

An object P lies between two parallel plane mirrors

M_{1}

and

M_{2} .

Its distance from the mirror

M_{1}

is 4 cm and the second image seen through the mirror

M_{2}

is at a distance of 22 cm from

M_{1} .

Find the distance between the mirrors.

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 2

A point source of light is situated between two parallel mirror

A

and

B

. The distance between the mirror is

3

cm and the object is

2

cm away form one mirror. How far is the third image behind

A

from the third image behind

B

?

HARD

12th West Bengal Board

IMPORTANT

A Text Book of PHYSICS PART 2 : CLASS 12>Chapter 12 - Reflection of Light>EXERCISE 12>Q 3

Find the angle between two plane mirrors in order that a ray incident on the first mirror in a direction parallel to the second may after reflection in second mirror retraces its path.

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