Question

Refer the attached picture. ​

Answer 1

Now using lens maker formula you can find focal length of one lens.

So it is:

1/f=1/50.

Now for double convex lens,

Using

I/F = 1/f + 1/f

1/F = 2/50

F=25 cm

Answer 2

Now using lens maker formula you can find focal length of one lens.

So it is:

1/f=1/50

Now for double convex lens,

Using

1/F =1/f+ 1/f

1/F = 2/50

F=25 cm

Thanks