Question

Light year is used to measure

• A. distance between stars
• B. distance between atoms
• C. revolution time of earth around sun
• D. none of the above

Answer 1

Answer: (A)

Light year is important unit of long distances
(to measure distance of stars, terrestrial objects).
One light year is the distance travelled by light in vacuum in one year.
As velocity of light in vacuum is
$3\times 10^{8}m{s}^{-1}$ and $1$ year $=365\times 24\times 60\times 60$ second,
therefore, $1$ light year
$=3\times 10^8\times (365\times 24\times 60\times 60)$ metre
$\therefore 1$ light year $=9.46\times 10^{15}m$