The distance between an electric lamp and a screen is `d=1m`. A convergent lens of focal length `f=21`cm is placed between the lamp and the lens such that a sharp image of the lamp filament is formed on the screen.

Options

A. The positions of the lens from the lamp for which sharp images are formed on the screen are 35cm and 65cm.
B. The positions of the lens from the lamp for which sharp images are formed on the screen are 35cm and 70cm
C. Magnitude of the difference in magnification is `40//21`
D. The size of the lamp filament for which there are two sharp images of 4.5cm and 2cm, is 3cm

Answer

b.,c.

Explanation

`(1)/(100-x)=(1)/(-x)=(1)/(21)`
`rArr` x, The distance of object from the lens is 30cm, 70cm
`m_(1)=(70)/(-30),m_(2)=(30)/(-70):.|m_(1)-m_(2)|=(40)/(21)`