Q.A star is emitting light at the wavelength of 5000 Å. Determine the limit of resolution of a telescope having an objective of diameter of 200 inch.

[!TLDR] $\theta=1.22\lambda/D$ with the 200-inch aperture converted to metres (5.08 m) gives $\theta\approx1.2\times10^{-7}$ rad. [!A …

The telescope resolving-power formula (Section 7.10.3) is $\theta_{min}=1.22\lambda/D$, with D the FULL objective diameter. Given the objective diameter as 200 inches, first convert to metres using $1\text{ inch}=0.0254$ m: $D=200\times0.0254=5.08$ m. With $\lambda=5000\text{ Å}=5\times10^{-7}$ m: $\theta_{min}=\dfrac{1.22\times5\times10^{-7}}{5.08}=\dfrac{6.1\times10^{-7}}{5.08}\approx1. …

Convert the given aperture from inches to metres, then substitute directly into the telescope's Rayleig …

Forgetting to convert the given 200-inch aperture to metres before substituting into the formula (which needs D and $\lambda$ in the SAME length unit), leading …