Question:easy

Light year is a unit of

Show Hint

Speed multiplied by time gives a length, so ask what light covers in one year.
Updated On: Jul 17, 2026
  • Distance
  • Time
  • Sound
  • Light intensity
Show Solution

The Correct Option is A

Solution and Explanation

The name is a trap. A light year sounds like a stretch of time because of the word year, but the definition settles it: a light year is how far light travels in vacuum in one year. Distance travelled equals speed multiplied by time, and the result of that product is a length.

Putting numbers in, light moves at about $3 \times 10^{8}$ m/s and a year has about $3.15 \times 10^{7}$ seconds, so one light year is close to $9.46 \times 10^{15}$ metres, or about 9.46 trillion kilometres. Astronomers need such a unit because star to star gaps are absurd in kilometres; Proxima Centauri, the nearest star to the Sun, sits about 4.24 light years away.

  1. Distance: Correct. Speed times time gives length, and the figure works out to roughly 9.46 trillion km.
  2. Time: This is the distractor the word year plants. Time is measured in seconds, and the year in the definition is only the interval used to fix how far the light goes.
  3. Sound: Sound has no bearing here. Loudness is measured in decibels and frequency in hertz, neither of which involves light travel.
  4. Light intensity: Luminous intensity is measured in candela and illumination in lux. Those describe how bright a source is, not how far light gets in a year.

So option (A) is correct.

Let's summarize:

  • One light year is about $9.46 \times 10^{15}$ m, an astronomical unit of length.
  • Other astronomical distance units are the astronomical unit and the parsec, about 3.26 light years.

A light year therefore measures distance.

Was this answer helpful?
0

Top Questions on General Science

Questions Asked in CLAT exam

Read the passage and answer the question.

Passage (extract): The work which Gandhiji had taken up was not only regarding the achievement of political freedom but also the establishment of a new social order based on truth and non-violence, unity and peace, equality and universal brotherhood and maximum freedom for all. A new order cannot be established without radically changing the mind and attitude of men towards property and, at some stage or the other, the 'haves' have to yield place to the 'have-nots'. We have seen, in our time, attempts to achieve a kind of egalitarian society and the picture of it after it was achieved. But this was done, by and large, through the use of physical force. It may even be that, like a gas kept confined within containers under great pressure, or water held back by a big dam, once the barrier breaks, the reaction will one day sweep back with a violence equal in extent and intensity to what was used to establish and maintain the outward egalitarian form. This enforced egalitarianism contains, in its bosom, the seed of its own destruction. If egalitarianism is to endure, it has to be based not on the possession of the maximum material goods by a few or by all but on voluntary, enlightened renunciation of those goods which cannot be shared by others or can be enjoyed only at the expense of others.

According to the passage, egalitarianism will not survive if
View Solution
Read the passage and answer the question.

Passage (extract): The work which Gandhiji had taken up was not only regarding the achievement of political freedom but also the establishment of a new social order based on truth and non-violence, unity and peace, equality and universal brotherhood and maximum freedom for all. This unfinished part of his experiment was perhaps even more difficult to achieve than the achievement of political freedom. In the political struggle, the fight was against a foreign power and all one could do was either join it or wish it success and give it his/her moral support. In establishing a social order on this pattern, there was a strong possibility of a conflict arising between diverse groups and classes of our own people.

According to the passage, which was the unfinished part of Gandhi's experiment?
View Solution
Read the passage and answer the question.

Passage (extract): In the political struggle, the fight was against a foreign power and all one could do was either join it or wish it success and give it his/her moral support. Experience shows that man values his possessions even more than his life because in the former he sees the means for perpetuation and survival of his descendants even after his body is reduced to ashes. We have seen, in our time, attempts to achieve a kind of egalitarian society and the picture of it after it was achieved. But this was done, by and large, through the use of physical force. This enforced egalitarianism contains, in its bosom, the seed of its own destruction. The root cause of class conflict is possessiveness or the acquisitive instinct.

Which of the following statements is 'not true' in the context of the passage?
View Solution