The star sirus is about 8.1 into 10 raise to 13 kilometre from the Earth assuming that the light travels at 3 into 10 raise to 5 kilometre per second find how long light from sirus takes to reach Earth.
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Given:
Distance of Sirius from earth = 8.1 * 10 ^{13} km
Speed of light = 3 * 10^{5} km/sec
As we know,
Speed = Distance/Time
However, we should not forget that the unit for distance is in kilometres and and the unit for speed is given in kilometre per second.
Therefore, we should multiply the speed with 3600,
3 * 10^{5} * 3600 km/h
⇒ 10800 * 10^{5} km/h
→ Time = Distance/Speed
Time taken by light from Sirius to reach Earth =
10800 * 10^{5} km/hr/8.1 * 10^{13} km
⇒1333.33 * 10^{-8} hr
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