IB Physics Higher Level (HL) Practice Exam

A light year is defined as the distance that light travels in a vacuum in one year. Light moves at a speed of approximately 299,792 kilometers per second, and over the course of a year, it covers a vast distance. Specifically, in one year, light travels about 9.46 trillion kilometers (or about 5.88 trillion miles). This unit of measurement is particularly useful in astronomy for expressing distances between stars and galaxies, which are often incredibly far away. The other options do not accurately capture this definition, as they reference time frames (one hour, one day, and one millennium) that are not in alignment with the standard definition of a light year. Thus, the correct answer affirms the essential relationship between light speed and the time frame of one year.