Which of the following is the unit of length? 

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RRB ALP Instrument Mechanic 23 Jan 2019 Official Paper (Shift 1)
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  1. Light year 
  2. Candela
  3. Lunar month
  4. Kelvin

Answer (Detailed Solution Below)

Option 1 : Light year 
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The correct answer is option 1

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 traveled by light in one year. 
    1.  A light-year is a convenient unit of measurement for large distances.
    2. Generally, a light-year is used to represent astronomical distances
    3. One light-year is approximately 9 trillion (9 × 1012) km.

Candela: It is a unit of luminous intensity in a given direction of a light source in the International System of Units (SI). Therefore, it's related to light's brightness, not length.

Lunar month: This relates to time, not length. It is an approximate period of 29.53 days that it takes for the Moon to go through one whole lunar phase cycle, from new moon to the next new moon.

Kelvin: It's a unit of thermodynamic temperature, one of the seven SI base units. It's used for measuring the warmth or coldness of an object or environment, not length.

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