# Units and Symbols

## Why do we need units?

At this point, we know all about voltage, current, and resistance. But, there is one problem: how do we refer to them? How do we define their quantity? If we don’t have any reference or a standard way, how would we know how much voltage does the power source generate or how much current is flowing through the circuit? Everything would become so confusing. To avoid this confusion we must use a standard way of defining quantities; this is done with the help of units.

## Unit of measurement

A * unit* is a definite way of representing any quantity. For e.g., smartphones come in different screen sizes such as 5 inches, 5.5 inches, 6 inches, etc. Here the numbers

**5**,

**5.5**, and

**6**are what is known as the

*, and the term*

**magnitude of a quantity***inches*is the

*. Any quantity cannot be represented without a magnitude or a unit. If we have the magnitude but not the unit, it will still remain difficult. E.g. a room’s height is 12; but 12 what? Same will be the case vice-versa.*

**unit of measurement**Just like we define the screen size of a Smartphone in **inches**, we have units to define voltage, current, and resistance as well.

- Voltage: We measure and define voltage in terms of
, which is also represented by the letter**volts****V**. For e.g., a regular AA battery has a voltage rating of**1.5 volts**, or**1.5V**. - Current: We measure and define current in terms of
, which is also written as the letter**amperes****A**. For e.g., the current rating of a Smartphone charger is**1 ampere**or**1A**. - Resistance is measured in terms of
, which is represented by the Greek alphabet**ohms****Ω**.

In your starter kit, you’ll find certain packages with resistors in them. You’ll see that different values are written on these packages, such as 220Ω, 1kΩ, and 1MΩ. Here, k and M are used to represent higher values of resistance. k stands for kilo, and M stands for mega. 1kΩ = 1000Ω and 1MΩ = 1000 kΩ = 1000000Ω.