# Question Video: Identifying the SI Base Unit of Length Physics

What is the SI base unit of length?

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### Video Transcript

What is the SI base unit of length? (A) Degree, (B) meter, (C) centimeter?

Okay, so in this question, we are being asked to identify the correct SI base unit of the physical quantity length. Let’s recall that length is a base quantity, also known as a fundamental quantity, and this means that it’s a quantity that cannot be separated into more fundamental parts. We can see that we are given three potential options for the SI base unit of length. Let’s begin by considering answer option (A), which claims that the SI base unit of length is the degree. We can recall though that degrees are actually a unit used for measuring angles. Since an angle is not the same thing as a length, then degrees cannot be a unit used to measure lengths. If the degree isn’t even a unit of length, then it certainly can’t be the SI base unit of length. This means that we can eliminate answer option (A).

Turning our attention now to the answers given in options (B) and (C), we can notice that both meters and centimeters are indeed valid units for measuring lengths. However, only one of these two options can be the SI base unit of length. We can notice that this bit meter appears in both of these two units. The centi- part of the word centimeter is a unit prefix. This prefix provides a useful modification of the meter, in this case meaning a factor of one over 100. So this unit prefix centi- is providing a modification to the units of meters where meters themselves are the SI base unit.

Our answer to this question then is given here in option (B). The SI base unit of length is the meter.