Speed of Light and Light Year – Rankers Physics
Topic: Ray Optics
Subtopic: Refraction by Plane Surfaces

Speed of Light and Light Year

Assertion (A): The speed of light in an optically rarer medium is greater than that in an optically denser medium.
Reason (R): One light year equals to \(9.5 \times 10^{12}\), km.
 
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution:

An optically rarer medium has a lower refractive index, meaning light travels faster in it, so A is true. A light-year is the distance light travels in one year, approximately \(9.46 \times 10^{12}\), km, so R is true. However, the definition of a light-year does not explain the speed of light in different media.

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