The objective and the eyepiece of a refracting astronomical telescope have focal lengths of 320 cm and 4.0 cm,respectively.The telescope is used to view Neptune and the final image is set at infinity.The diameter of Neptune is 4.96 × 10⁷m and the distance from the earth at the time of observation is 4.4 × 10¹²m.What is the angle (in mrad)subtended by the final telescopic image of Neptune? A) 0.90 mrad B) 1.1 mrad C) 1.3 mrad D) 1.5 mrad E) 1.7 mrad

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Quizplus · Accepted Answer

The angle subtended by the final telescopic image of Neptune is given by:$$	heta = \frac{d_o}{f_o} = \frac{4.96 	imes 10^7 	ext{ m}}{320 	ext{ cm}} = 1.55 	imes 10^{-3} 	ext{ rad} = 0.90 	ext{ mrad}$$

The Objective and the Eyepiece of a Refracting Astronomical Telescope