A convex lens of focal length 30 cm forms a real image three times larger than the object on a screen. Object and screen are moved until the image becomes twice the size of the object. If the shift of the object is 6 cm. The shift of screen is

Options

A. 28 cm
B. 14 cm
C. 18 cm
D. 16 cm

Answer

A

Explanation

(a) We have, `1/(3x)-1/(-x)=1/(+30)`
x=40 cm and 3x=120 cm

To decrease the magnification object should be move towards `2F_(1)`.
Hence, image will move towards `2F_(2)`. Let displacement is y.
Then,
2(40+6)=(120-y)(`thereforem=v/u`)
y= 28 cm