# (i)A pin of length 2 cm is placed perpendicular to the principal axis of a converging lens. An inverted image of size 1 cm is formed at a distance of 40 cm from the pin then focal length of lens and its distance from pin are what please explain the question with proper explanations

2
by rajusetu

2014-12-02T09:22:04+05:30

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H =  2 cm        h' = 1 cm
image is inverted =>  image is real.
m = - v/u = h'/h = -1/2
u = - 2 v
u is negative and v is positive

-u + v = 40 cm
3 v = 40  cm          =>  v = 40/3 cm
u = - 80/3 cm

1/f = 1/v - 1/u =  3/40 + 3/80 = 9/80

f  = 80/9 cm

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2014-12-02T20:01:43+05:30
H =  2 cm        h' = 1 cm
m = - v/u = h'/h = -1/2
u = - 2 v

-u + v = 40 cm
2v + v = 40 cm
3 v = 40  cm
v = 40/3 cm
u = - 80/3 cm

1/f = 1/v - 1/u =  3/40 + 3/80 = 9/80

f  = 80/9 cm