Question

Consider the following statements about Light year:

1. Light year is a unit for measurement of very large distances.

2. Light year is a unit for measurement of very large time intervals.

3. Light year is a unit for measurement of intensity of light.

Which of the statements given above is/are correct?

1. 1, 2 and 3
2. 2 and 3 only
3. 1 and 2 only
4. 1 only

Answer 1

Correct Answer - Option 4 : 1 only

CONCEPT:

• Length is a measure of the size or distance between two points. The SI unit of length is the meter (m).
• Light year: It is the distance travelled by light in one year. 
  • A light-year is a convenient unit of measurement of large distances.
  • Generally, a light-year is used to represent astronomical distances. 
  • One light-year is approximately 9 trillion (9 × 1012) km.

EXPLANATION:

• A light-year is a unit of length. Therefore option 4 is correct.​​
• It is the distance travelled by light in a vacuum in one year.
• A light-year is used in astronomy to measure the distances of nearby stars.

⇒ 1 light-year = 1ly = 9.467 × 1015 m

Parsec (parallactic second):

• It is the largest practical unit of distance used in astronomy.
• It is defined as the distance at which an arc of the length of 1 astronomical unit subtends an angle of 1 second of arc.

⇒ 1 parsec = 3.08 × 1016 m

Astronomical unit:

• It is defined as the mean distance of the earth from the sun. It is used in astronomy to measure the distance of planets.

 1 astronomical unit = 1 AU = 1.496 × 1011 m