Question

Two thin lenses when in contact have power of 10D . When they are .25m apart the power reduce to 6D The focal lens of lens 1 And lens 2 is

Answer 1

LET THE POWER OF THE TWO LENSES BE P1 AND P2. SO THE FORMULA IN FINAL POWER =P1+P2-DISTANCE BETWEEN THEM MULTIPLIED BY P1P2 P=P1+P2-dP1P2(MATHEMATICAL REPRESENTATION) IN THE FIRST CASE DISTANCE BETWEEN THE LENSE IS O THEREFORE d BECOMES O AND WE GET P =P1+P2 LET THIS BE EQUATION 1.. NOW IN THE SECOND CASE d is 0.25 SO EQUATION 2 BECOMES P=P1+P2-0.25P1P2 SOLVING THE TWO EQUATIONS WE GET P1=8 and P2 =2 orP1=2 and P2 =8 f1= 0.5 or 0.125 m f2= 0.125 or 0.5 m