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Physics is an experimental science. The physical phenomenon and methods around us are quantitatively measured using physical quantities. Given below is a list of basic SI units and their symbols.

 Quantity Unit Symbol Length meter (m) l Mass kilogram (kg) m Time second (s) t Current ampere (A) I Temperature kelvin (K) T

## Units & Prefixes

Physical quantities can either be very large or they can be very small. For example, the standard size of a soccer field is about 100 meters long while a 50 pence coin is 27.3 mm in diameter.

mm stands for millimeter where milli is a prefix whose value is 10-3.

For instance, 1 meter has 1000 millimeters. 1 m = 1000 mm

For ease of measurements usually, we have to convert from one prefix to another.

Given below are some useful conversions for most commonly used physical quantities and their units.

## Length

• 1 nanometer (nm) = 10-9 m
• 1 micrometer ( μm) = 10-6 m
• 1 millimeter (mm) = 10-3 m
• 1 centimeter (cm) = 10-2 m
• 1 kilometer (km) = 103 m

## Mass

• 1 milligram (mg) = 10-3 g
• 1 kilogram (kg) = 103 g

## Time

• 1 nanosecond (ns) = 10-9 s
• 1 microsecond (μs) = 10-6 s
• 1 millisecond (ms) = 10-3 s

## Current

• 1 nano-ampere (nA) = 10-9 A
• 1 micro-ampere ( μA) = 10-6 A
• 1 milli-ampere (mA) = 10-3 A