AP EAMCET2012PhysicsRay Optics
The objective and eyepiece of an astronomical telescope are double convex lenses with refractive index 1.5. When the telescope is adjusted to infinity, the separation between the two lenses is 16 ~cm . If the space between the lenses is now filled with water and again telescope is adjusted for infinity, then the present separation between the lenses is
Options
- A8 ~cm
- B16 ~cm
- C24 ~cm
- D32 ~cm
Correct answer
D. 32 ~cm
Step-by-step solution
From the lens maker formula array cc & ₃ v - ₁ u = ₂- ₁ R₁ + ₃- ₂ R₂ & 4 3 f_o ^ - 1 = 1.5-1 R + 4 3 -1.5 -R f_o ^ =R=2 f array Now, length =f_o ^ +f_e ^ aligned & =2 f_o+2 f_e=2 (f_o+f_e ) & =2(L)=2(16)=32 ~cm aligned