Previous Year Question
What does a light-year represent?
A.
The distance travelled by light in vacuum in one year
B.
The speed of a rocket measured in one year
C.
The speed of an aeroplane
D.
The distance travelled by sound in vacuum in one year
Correct Answer: A
Detailed Solution
A light-year is the distance travelled by light in vacuum in one year. Therefore, it is a unit of distance. According to NASA, light travels through vacuum at approximately 3 × 10⁵ km/s and covers about 9.46 × 10¹² km in one year.
Thus, a light-year is not related to the speed of a rocket or aeroplane, nor to the distance travelled by sound.
Important fact: The Hindi question as printed contains the expression “पुरातात्विकमापपट्टन,” which is not scientifically appropriate in this context. The intended concept is the definition of a light-year as a measure of astronomical distance.