Question

The diameter of the moon is $33.5\times$${10}^3$ $km$ and its distance from earth is $53.8\times 10$${}^5$ $km$. The focal lengths of the objective lens and eye piece of a telescope are $400cm$ and $10cm$ respectively. When viewed through the telescope, the diameter of the image of moon will appear as:

• A. 2 cm
• B. 2.5 cm
• C. 3 cm
• D. 5 cm

Answer 1

Answer: (B)

2.5 cm

The diameter (d) of the moon appear when viewed through the telescope is:

$d=\frac{D.f}{S}=\frac{33.5\times {10}^3\times 4}{53.8\times {10}^5}=2.5cm$