Question

Q19. (a)A convex lens has a focal length of 10 cm. At what distance from the lens
should the object be placed so that it forms a real and inverted image 20 cm away from
the lens?
(b) What would be the size of the image formed if the object is 2 cm high?
(c) With the help of a ray diagram show the formation of the image by the lens in this
case.​

Answer 1

Answer:

Focal length=f=10cm

Image distance=v=20cm

Using sign convention,

f is positive,v is also positive

Lens formula,

1/f=1/v-1/u

1/10=1/20–1/u

1/u=1/20–1/10

1/u=(10–20)/200

1/u=-10/200

u=-20

Object distance=20cm(minus indicates that the lens is converging lens)

hi=height of image and ho=height of object

hi/ho=-v/u

hi/2=-20/20

hi=2cm

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