Which physical quantity does a $\text{light-year}$ measure?

• A. $\text{Volume}$
• B. $\text{Distance}$
• C. $\text{Speed}$
• D. $\text{Time}$

Answer: (B)

Verified step by step guidance

1. Understand that a light-year is a unit used in astronomy and physics to describe how far light travels in one year.
2. Recall that light moves at a constant speed in vacuum, approximately \(3 \times 10^{8}\) meters per second.
3. Recognize that since a light-year is defined by the distance light covers over a specific time period (one year), it is a measure of distance, not time, speed, or volume.
4. Express the light-year mathematically as the product of the speed of light and the time interval of one year: \(\text{Light-year} = \text{speed of light} \times \text{time} = c \times t\).
5. Conclude that the physical quantity measured by a light-year is distance.