### SI Unit System - Q&A

Q1: What is the definition of a quantity?
A quantity is a physical measurement, such as length, time, volume, area, energy, temperature, and mass. Hundreds of different quantities are used in science, technology, and everyday life. Quantities are represented with italic letter symbols like length (l) and mass (m)

Q2: How to represent a specific quantity?
A specific quantity consists of a number times a unit like specific quantity of length will be represented by (5 m) means 5 number of meters.

Q3: What is the definition of the SI unit?
SI unit is a standard measurements for Quantity which may be length or mass or else.

Q4: How the SI units be represented?
We usually write units with symbols rather than spelling them out. For example, 5 m is a quantity (length) consisting of the number 5 times the unit meter (m). They are symbols, not abbreviations, and are case sensitive. Always leave a space between the number and unit.

Q5: What is the definition of the SI base units?
SI base units are standard measurements for quantities and

The SI has (6) nos. base units which are shown in fig.1
fig.1

Q6: What is the definition of the SI derived units?
SI derived units are derived by multiplying, dividing, or powering SI base units in various combinations like force (F) with unit name Newton and unit symbol (N) which equal kg.m/s2

Q7: What is the definition of the coherent SI derived units?
Coherent SI derived units system, which means that derived units are defined by the same laws or equations as the quantities they measure. For example, the quantity called speed (v) is defined as distance per time. Per means “divided by.” Distance is a kind of length. In symbols,

v = d/t (definition of speed)

The SI unit of speed is therefore meter per second—the unit of length divided by the unit of time. In symbols, you can show division three different ways: a slash, horizontal bar, or negative exponent. For example, you may write “8 meters per second” as Q8: What are the types of the coherent SI derived units?
The types of the coherent SI derived units are :

• Coherent SI derived units without special names
• Coherent SI derived units without special names

The two types are represented in fig.2

fig.2

Q9: What is the total numbers of SI units?
The total numbers of SI units is 30 nos. as shown in fig.3

fig.3

Q10: What is the definition of Prefixes?
Prefixes are short names and letter symbols for numbers (powers of ten). A prefix may be attached to the front of a unit to form a multiple of the unit. It does not form a separate unit. For example, the prefix kilo (k) means 1000, so kilometer (km) means 1000 meters.

Q11: What is the total numbers of Prefixes?
The total numbers of Prefixes is 20 nos. as shown in fig.4
fig.4

Q12: What are the approved non-SI units?
The approved non-SI units are shown in fig.5
fig.5