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JEE Main 2015 (10 Apr, Shift 1) · Optical Instruments & the Eye

Optical Instruments & the Eye question from JEE Main 2015 (10 Apr, Shift 1)

Q41JEE Main 2015 · 10 APR · SHIFT 1Medium

Optical Instruments & the Eye

A telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. If a 50 m tall tower at a distance of 1 km is observed through this telescope in normal setting, the angle formed by the image of the tower is $\theta$ , then $\theta$ is close to:

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Answer: (d)

Angle subtended by tower: $\alpha = \dfrac{50}{1000} = 0.05$ rad.
$M = \dfrac{f_o}{f_e} = \dfrac{150}{5} = 30$ .
$\theta = M\alpha = 30 \times 0.05 = 1.5$ rad $\approx 86^\circ$ .
The closest option is (d) $60^\circ$ .

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