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Question : 31 of 33
Marks: +1, -0
The farthest objects in our Universe discovered by modern astronomers are so distant that light emitted by them takes billions of years to reach the Earth. These objects (known as quasars) have many puzzling features, which have not yet been satisfactorily explained. What is the distance in km of a quasar from which light takes 3.0 billion years to reach us?
Solution:  
Time taken, t=3×109t=3 \times 10^{9} years
=3×109×365×24×60×60s=3 \times 10^{9} \times 365 \times 24 \times 60 \times 60 \text{s}
Velocity of light, c=3×108 m s−1c=3 \times 10^{8} \ \text{m} \ \text{s}^{-1}
∴\therefore Distance of quasar from earth =ct=c t
=3×108×3×109×365×24×3600 m=3 \times 10^{8} \times 3 \times 10^{9} \times 365 \times 24 \times 3600 \ \text{m}
=2.84×1025 m=2.84 \times 10^{25} \ \text{m}
=2.84×1022 km=2.84 \times 10^{22} \ \text{km}
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