NEETPhysicsRay Optics
An astronomical telescope in normal adjustment is constructed using two convex lenses of optical powers +0.5 ~D and +25 ~D . Match the parameters of the telescope in List-I with their corresponding values in List-II. List-I List-II (A) Tube length (I) 200 ~cm (B) Magnitude of magnifying power (II) 4 ~cm (C) Focal length of objective (III) 204 ~cm (D) Focal length of eyepiece (IV) 50 Choose the correct answer from the
Options
- A(A)-(III), (B)-(IV), (C)-(I), (D)-(II)
- B(A)-(III), (B)-(IV), (C)-(II), (D)-(I)
- C(A)-(I), (B)-(III), (C)-(IV), (D)-(II)
- D(A)-(IV), (B)-(III), (C)-(I), (D)-(II)
Correct answer
A. (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
Step-by-step solution
For an astronomical telescope, the objective lens must have a larger focal length and the eyepiece must have a smaller focal length. Given powers: P₁ = +0.5 ~D and P₂ = +25 ~D Focal lengths are: f₁ = 1 P₁ = 1 0.5 ~m = 2 ~m = 200 ~cm f₂ = 1 P₂ = 1 25 ~m = 0.04 ~m = 4 ~cm Thus, focal length of objective, f_o = 200 ~cm (C I) Focal length of eyepiece, f_e = 4 ~cm (D II) In normal adjustment, the tube length is: L = f_o + f_e = 200 + 4 = 204 ~cm (A III) Magnitude of magnifying power is: |m| = f_o f_e = 200 4 = 50 (B IV)