Question

Light year is the unit of distance. It is the distance travelled by light in one year. If the speed of light is equal to $3\times {10}^8\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$ , how many kilo-meters will make up $1$ light year?

Answer 1

One light-year:

One light-year is defined as the distance which light travels in one year.

Explanation:

$1$ Light year = speed of light x time in seconds

Speed of light = $3\times {10}^8\raisebox{1ex}{$m$}\!\left/ \!\raisebox{-1ex}{$s$}\right.$

Time (second) in one year = $365\times 24\times 60\times 60sec$

$$\begin{gathered} 1lightyear=3\times {10}^8\times 365\times 24\times 60\times 60 \\ =9.46\times {10}^{15}m. \\ =9.46\times {10}^{12}km. \end{gathered}$$

Hence, in $1$ light year, the light will travel a distance of $9.46\times {10}^{12}km.$