An astronomical telescope in normal adjustment has an objective lens of focal length and an eyepiece of focal length . What is the magnifying power and the separation between the lenses?

Answer and explanation

Correct answer: D.

  1. Step 1: In normal adjustment (image formed at infinity), the magnifying power of an astronomical telescope is .
  2. Step 2: Substitute values: .
  3. Step 3: The distance between objective and eyepiece (length of the telescope tube) is .
Answer
.
Why not the others: subtracts the focal lengths (); multiplies focal lengths (); uses .

Practise more Ray optics and optical instruments.

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