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Diameter of the objective lens of a telescope is 250 cm. For light of wavelength 600 nm, coming from a distant star, the limit of resolution of the telescope if close to it is

1. 2.0 × 10⁻⁷ rad
2. 4.5 × 10⁻⁷ rad
3. 1.5 × 10⁻⁷ rad
4. 3.0 × 10⁻⁷ rad

Correct answer: 3.0 × 10⁻⁷ rad

Solution

Resolution limit = 1.22*lambda/D = 1.22*(600e-9)/2.5 = 2.93e-7 rad, which is close to 3.0 x 10^-7 rad.

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