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Question
A particular star is at a distance of about 8.1 × 1013 km from the Earth. Assuring that light travels at 3 × 108 m per second, find how long does light takes from that star to reach the Earth.
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Solution
The distance between Star and Earth = 8.1 × 1013 km = 8.1 × 1013 × 103 m
Since, light travels at 3 × 108 m per second.
So, time taken by light to reach the Earth = `(8.1 xx 10^13 xx 10^3)/(3 xx 10^8)`
= `(8.1 xx 10^16)/(3 xx 10^8)`
= `8.1/3 xx 10^8`
= 2.7 × 108 s
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