SECTION 8.2 ELECTRIC CURRENT

In order to utilize electrical current in a battery a connection has to be made from one electrode to another electrode. This connection is called an electric circuit. Generally, within an electric circuit we want to transform electrical energy into another form of energy which is called the electric load of the circuit.

What is an electric load? An electric load is essentially anything in the circuit that uses electricity to do work. Examples Light bulb  light Heater  heat Speaker  sound Car starter  mechanical energy

There are many different kinds of circuits that perform a variety of operations however; there are four (4) basic kinds of components in a circuit which include:

1. SOURCE Source Where the electrical energy comes from (e.g. battery) Note: Batteries are made up of cells.

Conductor How the electric energy travels from the source (e.g. wire)

3. Load Load A device that transforms electrical energy into another form of energy (e.g. light bulb).

4. Switch Switch A device that can turn the circuit on or off by opening or closing the circuit (e.g. light switch).

An extra note on circuits When a switch is open, the circuit is said to be open. When the switch is closed, the circuit is said to be closed. Remember: A complete circuit has no gaps in it (everything is connected to something else). If you do not attach all of the wires correctly, the circuit will not work!

There are many ways one can explain an electric circuit There are many ways one can explain an electric circuit., but the most common and easiest way is with a circuit diagram. A circuit diagram uses symbols to represent the basic components of the circuit.

KEY FEATURES OF A CIRCUIT DIAGRAM Circuit diagrams are: Neat and tidy (use a ruler on paper) Make all connecting wires and leads with straight lines at 90 degree angles Avoid drawing conductors over top one another (use a semi-circle if unavoidable) Your finished diagram should always be square or rectangular.

Draw this circuit as a diagram. Draw a circuit diagram Draw this circuit as a diagram.

Without a complete circuit, the battery has nowhere to push electrons Without a complete circuit, the battery has nowhere to push electrons. With a completed circuit, electrons flow from the negative terminal through a conductor to a load, then finally to the positive terminal of the battery. This flow of electrons within a circuit is called current (I) and this concept can be thought of as electricity.

We use the symbol To represent an ammeter in a circuit drawing.

Electric current is defined as the amount of charge passing a point in a conductor every second (s). It is measured in ampres (A), named after the French physicist Andre-Marie Ampere.

In order to measure current we use a device called an ammeter In order to measure current we use a device called an ammeter. Unlike a voltmeter where you connect across two points in a circuit, an ammeter must be connecting inline with the circuit (note: 1.0A = 1000 mA).

According to Benjamin Franklin, charges objects flowed from positive to negative as the positive charge contained more electric fluid. This is contrary to our current understanding where electrons flow from negative to positive. For historical reasons, we refer to Franklin’s idea as conventional current as it is still used today to calculate potential difference in a circuit.