An electronic circuit consists of electronic parts, connected by wires.

#### The properties of the electronic circuits and the relations between them

Every point of an electronic circuit has a specific level of voltage. We usually do not know what the level of voltage actually is. Instead we usually can only say what the voltage difference between two points is. The mathematic symbol for voltage is U, the unit for voltage is Volt.

A specific amount of current flows through every point of every electronic circuit. The mathematic symbol for current is I, the unit for current is Ampere.

Both things, voltage and current, are related to each other: If there is a voltage difference between two points, current will always try to flow from the one point to the other. How much current can actually flow, is defined by the resistance between these two points. The mathematic symbol for resistance is R, the unit for resistance is Ohm.

The relation can be expressed in a clear mathematical formula:

`U in Volt = I in Ampere * R in Ohm`

When a voltage difference makes current flow, electrical energy is “used” and transformed into something else, such as heat (with resistors, see below), light (with LEDs, for example), sound (with speakers) or anything else. The amount of energy “used” is defined by the voltage multiplied with the current:

`P in Watt = U in Volt * I in Ampere`

#### Very simple example

Lets take a look at a simple electronic part: A battery.

A battery is a source of electrical power: It is a part which builds a constant voltage difference between its two poles. If somebody says that a battery has a voltage of 1.5 V, the person actually means that the battery builds a constant voltage difference of 1.5 V between its two poles: The voltage at the + pole will usually be 1.5 V higher than the voltage at the – pole.

Now let’s take a look at another simple electronic part: A resistor

A resistor is one of the simplest consumers of electrical power. It transforms electronical energy into heat.

It has a specific resistance. You can get resistors for many difference resistance values, for example for 1 Ohm, 100 Ohm or even 1 Mega Ohm.

Lets get a resistor with a resistance of 100 Ohm and connect it to a 1.5 V battery:

The current flowing though it will be 1.5 V / 100 Ohm = 0.015 A (which is 15 mA). The electronical energy consumed and converted into heat would be 1.5 V * 0.015 A = 0.0225 Watt.

#### What’s next?

In our next blog post we will build on the knowledge gained here and learn how to make a small LED (those small lights used everywhere nowadays) light up in an electric circuit. This is not as easy as connecting an LED directly to a battery, because an LED needs an exact voltage which is usually more than what one battery delivers and less than what multiple batteries deliver.

Thank you for reading!