Question

The distance travelled by light in one year is called
(A) Light Year
(B) Light Distance
(C) Both \[\left( {\mathbf{A}} \right){\text{ }}{\mathbf{and}}{\text{ }}\left( {\mathbf{B}} \right)\]
(D) None of these

Answer 1

Hint:To solve this question,we should know velocity of light and we must have knowledge about calculating seconds for one year.

Complete step by step answer:
The light travels at a speed of \[3 \times {10^8}\]$\dfrac{m}{s}$
In one minute there are \[60sec,\] and in one hour there are\[3600{\text{ }}sec\], and in one day it is \[86,400{\text{ }}sec\] and for a year it is \[31,536,000sec.\]
So light travels at a distance of \[9,460,800,000,000,000meters{\text{ }}or{\text{ }}9,450,800,000,000km\] in a year.
A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about \[300,000\;kilometres\;\left( {km} \right)\]each second. So in one year, it can travel about \[10{\text{ }}trillion{\text{ }}km\]. More precisely, one light-year is equal to \[9,500,000,000,000{\text{ }}kilometres.\]
Why would you want such a big unit of distance? Well, on Earth, a kilometre may be just fine. It is a few hundred kilometres from New Delhi to Ghaziabad; it is a few thousand kilometres from New Delhi to Pune. In the universe, the kilometre is just too small to be useful. For example, the distance to the next nearest big galaxy, the Andromeda Galaxy, is \[21{\text{ }}quintillion{\text{ }}km.{\text{ }}That's{\text{ }}21,000,000,000,000,000,000{\text{ }}km.\]
This is a number so large that it becomes hard to write and hard to interpret. So astronomers use other units of distance.
So, the distance travelled by light in one year is called Light Year. Since it is a unit of length which is measured using light we can also call it as Light Distance.
So Option \[\left( C \right)\] is correct.

Note:Light year is a unit of length but not a unit of time.