AP EAMCET Engineering 26 Apr 2017 Shift 1 Paper

The figure below represents the convex lens and two point sources,
The given condition satisfies when S1 is placed in one sie such that u<f and the S2 is placed on the other side of the lens such that u>f .
S1 is the object for lens, from lens formula,

1

f

=

1

−y

−

1

−x

1

y

=

1

x

−

1

−f

........(I)
S2 is the object for the lens, then

1

f

=

1

y

−

1

−(24−x)

1

−y

=

1

f

−

1

24−x

......(II)
From equation (I) and (II),

1

x

−

1

f

=

1

f

−

1

24−x

1

x

−

1

9

=

1

9

−

1

24−x

1

x

+

1

24−x

=

2

9

x2−24x+108=0
By solving the above equation,
x=6‌cm or 18‌cm