1.

(i) Define optical centre of spherical lens. (ii) A divergent lens has a focal length of 20 cm. At what distance should an object of height 4 cm from the optical centre of the lens be placed so that its image is formed 10 cm away from the lens. Find the size of the image also. (iii) Draw a ray diagram to show the formation of image in above situation.

Answer»

SOLUTION :(i) Optical centre: the central point of a lens.
(II) f=-20 cm
`h_(1)=4cm, v=-10 cm`
`U=?,h_(2)=?`
`1/f=1/v-1/u`
`1/u=(-1)/10+1/20=(-1)/10+1/20`
`=(-20+1)/20=-1/20`
`u=-20cm`
`h_(1)=v/u h_(0)`
`=(-10cm)/(-20cm) xx4cm=2cm`


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