Answer:
Explanation:
The image is formed on a screen therefore image must be real and lens must be convex.
So it must have been formed on the other side of the lens.
U, object distance = - 40 cm ;
V, image distance = 40 cm ;
Len formula
[tex]\frac{1}{v} -\frac{1}{u} =\frac{1}{f}[/tex]
Putting the given values
[tex]\frac{1}{40} +\frac{1}{40} =\frac{1}{f}[/tex]
[tex]\frac{2}{40} =\frac{1}{f}[/tex]
f = 20 cm .
