Wave Optics

JEE Main level, single correct, medium

148 of 191

Question 148 of 191

Two stars are 10 light years away from the earth. They are seen through a telescope of objective diameter 30 cm. The wavelength of light is 600nm. To see the stars just resolved by the telescope, the minimum distance between them should be (1lightyear=9.46×1015m)\left(1lightyear=9.46\times {10}^{15}m\right) of the order of :

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Answer: (A) 108km{10}^{8}km

l=Ra1.22×λl=\dfrac{R}{a}1.22\times \lambda

and a=30cma = 30cm

⇒l=9.46×1015×10×1.22×600×10−90.3\Rightarrow l=\dfrac{9.46\times {10}^{15}\times 10\times 1.22\times 600\times {10}^{-9}}{0.3}

=2.30×1011m=2.30\times {10}^{11}m

⇒2.30×108km\Rightarrow 2.30\times {10}^{8}km

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