At what distance from a concave lens of focal length 20 cm, a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed. Draw a ray diagram to justify your answer for the above situation and label it.

At what distance from a concave lens of focal length 20 cm, a 6 cm tal

1.	At what distance from a concave lens of focal length 20 cm, a 6 cm tall object be placed so as to obtain its image at 15 cm from the lens? Also calculate the size of the image formed. Draw a ray diagram to justify your answer for the above situation and label it.
Answer» Solution :`f=-20CM,h_(1)=6cm,v=-15cm, u=?` LENS formula `1/f=1/v-1/u` `impliesu=(VF)/(f-v)` `(-15cmxx-20cm)/(-20cm-(-15cm))` `=-60CM` object at 60 cm from the lens `h_(2)=v/uxxh_(1)` `=(-15cm)/(-60cm)xx6cm` `=+1.5cm` diiminished erect