Question

Give the substance-
Books introduce us into the best society. They bring us into the presence of the greatest minds that have ever lived. we here what they said and did. we see them as if they were really alive. We share their thoughts,grieve with them. We feel as if we acted with them in the scenes which they describe. All books are probably record of the history of the past men, What thoughts past men had in them, what actions past men did.​

Answer 1

Solution :-

First, we have to find the image distance :

\implies \sf \dfrac{- v}{u} =\: \dfrac{3\cancel{h_o}}{\cancel{h_o}}⟹

u

−v

=

h

o

3

h

o

\implies \sf \dfrac{- v}{u} =\: 3⟹

u

−v

=3

By doing cross multiplication we get,

\implies \sf - v =\: 3u⟹−v=3u

\implies \sf \bold{\purple{v =\: - 3u}}⟹v=−3u

Now, we have to find the object distance :

Given :

Image Distance (v) = - 3u

Focal Length (f) = - 20 cm

\longrightarrow \sf \dfrac{1}{- 20} =\: \dfrac{1}{- 3u} + \dfrac{1}{u}⟶

−20

1

=

−3u

1

+

u

1

\longrightarrow \sf \dfrac{1}{- 20} =\: \dfrac{- 1 + 3}{3u}⟶

−20

1

=

3u

−1+3

\longrightarrow \sf \dfrac{1}{- 20} =\: \dfrac{2}{3u}⟶

−20

1

=

3u

2