1) Two convex lenses of power 2D and 5D are separated by a distance 1/3 m . The power of optical system formed is A) +2D B) -2D C) -3D D) +3D Answer: Option DExplanation: Given P1 =2D ; p2= 3D $d=\frac{1}{3}m$ we know that $\frac{1}{F}=\frac{1}f_{1}+\frac{1}f_{2}-\frac{d}{f_{1}.f_{2}}$ Equivalent power, $\therefore$ P=P1+P2 -d P1.P2 = $2+3-\frac{1}{3}\times2\times3=3D$
