The meter is presently defined as
A) one ten-millionth of the diameter of Earth.
B) the wavelength of a line in the spectrum of krypton-86.
C) the length of a platinum-iridium bar.
D) the distance light travels in a vacuum in a very short time.

Question

Quizplus · Accepted Answer

The meter is currently defined as the distance light travels in a vacuum in 1/299,792,458 of a second, making option D the correct answer. This definition was adopted in 1983 by the 17th General Conference on Weights and Measures, reflecting the constant speed of light in a vacuum as a fundamental physical constant.

The Meter Is Presently Defined as