Which of the following is the basis of the current standard for the $meter$?

• A. The distance traveled by light in vacuum during a specific fraction of a $second$
• B. The length of a platinum-iridium bar kept in Paris
• C. The wavelength of orange-red light emitted by $k_{86}$ (krypton-86)
• D. The circumference of the Earth at the equator

Answer: (A)

Verified step by step guidance

1. Understand that the problem asks about the basis of the current standard for the meter, which is a unit of length in the International System of Units (SI).
2. Recall that historically, the meter was defined by physical objects or natural phenomena, such as the length of a platinum-iridium bar or the wavelength of light emitted by krypton-86.
3. Recognize that modern definitions aim for greater precision and reproducibility, so the meter is now defined based on a fundamental constant of nature.
4. Know that the current standard defines the meter as the distance light travels in vacuum during a specific fraction of a second, linking the unit of length to the constant speed of light.
5. Therefore, the correct basis for the current meter standard is the distance traveled by light in vacuum during a defined time interval, ensuring high precision and universality.