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JEE Main 2026 · 4 Apr · Shift 1, Physics question 44

A telescope with objective diameter RR is used to observe a distant star emitting light of wavelength 500 nm, at a resolution of 5×10−75\times10^{-7} radian. The value of RR is ________ cm.

Choose one option
Answer and worked solution

Official answer: B

Rayleigh criterion. θ=1.22λD\theta=1.22\dfrac\lambda D, so
D=1.22×500×10−95×10−7=1.22 m=122 cm.D=\frac{1.22\times500\times10^{-9}}{5\times10^{-7}}=1.22\text{ m}=122\text{ cm}.

(B)

Topics:Optical instrumentsDiffraction
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