A-convex-lens-of-focal-length-10cm-is-used-to-form-a-real-image-which-is-half-the-size-of-the-object-how-far-from-the-object-is-the-image-

Question Number 132991 by aurpeyz last updated on 17/Feb/21

A c o n v e x l e n s o f f o c a l l e n g t h 10 c m

i s u s e d t o f o r m a r e a l i m a g e w h i c h i s

h a l f t h e s i z e o f t h e o b j e c t . h o w f a r

f r o m t h e o b j e c t i s t h e i m a g e ? ? ?

Commented by aurpeyz last updated on 17/Feb/21

p l s h e l p m e

Answered by mr W last updated on 17/Feb/21

Commented by mr W last updated on 17/Feb/21

u = - 2 v

- \frac{1}{u} + \frac{1}{v} = \frac{1}{f}

- \frac{1}{- 2 v} + \frac{1}{v} = \frac{1}{f}

\frac{3}{2 v} = \frac{1}{f}

\Rightarrow v = \frac{3 f}{2} = 15 c m

\Rightarrow u = - 3 f = - 30 c m

d i s t a n c e o b j e c t f r o m i m a g e

= 30 + 15 = 45 c m

Commented by aurpeyz last updated on 17/Feb/21

m = \frac{1}{2} = \frac{- v}{u} ≫ u = - 2 v

f = + 10 c m

\frac{1}{10} = \frac{1}{- 2 v} + \frac{1}{v} \Rightarrow v = 5 c m . . u = 10 c m

v + u = 15 c m

i s i t r i g h t ?

Commented by aurpeyz last updated on 17/Feb/21

p l s w h y d o e s t h e f o r m u l a (l i n e 2)

s t a r t s w i t h - v e ?

Commented by mr W last updated on 17/Feb/21

i {c a n}^{'} t a n d {d o n}^{'} t w a n t t o t e a c h y o u

e l e m e n t a r y t h i n g s . i f y o u h a v e

p r o b l e m s t o r e m e m b e r t h e f o r m u l a

a n d t h e c o r r e s p o n d i n g s i g n

c o n v e n t i o n, y o u s h o u l d u n d e r s t a n d

t h e p h y s i c s i t s e l f a s t h e p i c t u r e

s h o w s . {l e t}^{'} s f o r g e t t h e f o r m u l a a n d

s i g n c o n v e n t i o n, w e t a k e f, u, v a l l

a s p o s i t i v e . w h a t c a n w e g e t f r o m

t h e p i c t u r e a b o v e ? w e g e t :

\frac{A^{'} B^{'}}{A B} = \frac{1}{2}, s i n c e i m a g e = \frac{1}{2} o b j e c t s i z e

\frac{F_{2} B}{{O F}_{2}} = \frac{A^{'} B^{'}}{O C} = \frac{A^{'} B^{'}}{A B} = \frac{1}{2}

\Rightarrow \frac{v - f}{f} = \frac{1}{2} \dots (i)

\Rightarrow v = \frac{3 f}{2} = 15 c m

\frac{{O B}^{'}}{O B} = \frac{A^{'} B^{'}}{A B} = \frac{1}{2}

\Rightarrow \frac{v}{u} = \frac{1}{2} \dots (i i)

\Rightarrow u = 2 v = 3 f = 30 c m

Commented by aurpeyz last updated on 18/Feb/21

t h a n k y o u s i r

Commented by mr W last updated on 18/Feb/21

Commented by aurpeyz last updated on 18/Feb/21

t h a n k y o u s i r

Facebook Tweet Pin