AP EAMCET2002PhysicsRay Optics
A convex lens of focal length 0.15 ~m is made of a material of refractive index 3 2 . When it is placed in a liquid, its focal length is increased by 0.225 ~m . The refractive index of the liquid is
Options
- A7 4
- B5 4
- C9 4
- D3 2
Correct answer
B. 5 4
Step-by-step solution
f_a=0.15 ~m , _g=3 / 2, f_e=0.225+0.15 From lens formula, For air, 1 f_a = ( _g _a -1 ) ( 1 R₁ - 1 R₂ ) For liquid, 1 f_l = ( _g _l -1 ) ( 1 R₁ - 1 R₂ ) aligned 1 / f_a 1 / f_l & = ( _g / _a-1 ) ( _g _l -1 ) f_l f_a & = ( 3 / 2 1 -1 ) ( 3 / 2 _l -1 ) 0.375 0.15 & = 1 / 2 ( 3 2 _l -1 ) ( 3 2 _l -1 ) & = 1 / 2 5 / 2 3 2 _l -1 & = 1 5 3 2 _l & = 1 5 +1 3 2 _l = 6 5 _l & = 5 4 aligned