Electric Current

8.2

THE CIRCUIT

• Electric Current – flow of charged particles (electrons) in a complete circuit.

• Electric circuit – a complete pathway that allows electrons to flow.

ENERGY AROUND A CIRCUIT

• Electric Load – any device that transforms electrical energy into other forms of energy.

Examples: light bulb, buzzer, heater, motor

• Figure 8.9 - Page 281

CIRCUIT COMPONENTS AND DIAGRAMS

Circuits are made up of four basic parts:

1. Source – source of electrical energy.

2. Conductor – the wire that electric current flows.

3. Load – a device that transforms electrical energy into other forms of energy.

4. Switch – a device that can turn the circuit on or off by opening/closing the circuit.

CIRCUIT SYMBOLS

Cell Light bulb Wires

Ammeter Voltmeter Resistor

Fuse Open Switch Closed Switch

A V

DRAWING CIRCUITS

• Always in a rectangular shape

• Must use a ruler

• Lines represent wires

• Use appropriate symbols to represent parts of the circuit

• All circuits have: source, load, conductor, switch

• Drawing Circuit diagrams pg. 283 #1-3

ELECTRONS ARE SO PUSHY

• Electrons apply an action-at-a-distance force

• This means electrons do not need to touch in order to push other electrons

CURRENT ELECTRICITY AND STATIC CHARGE

• The charge in a battery is not an example of static electricity, even though the charge

remains very nearly fixed on the battery terminals when the battery is not connected to a

closed circuit

• This continuous flow of charge in a complete circuit is called current electricity

• Electrons travel only about 0.5mm/s in a circuit

CURRENT: THE MEASURE OF FLOW

• Is defined as one coulomb of charge passing a given point per second.

• The flow of electrons from the negative terminal to the positive terminal through a wire (due to the difference in voltage between the positive and negative terminals).

• Unit of Current – amperes (A)

• Ammeter – used to measure the electric current flowing in wires.

CIRCUIT FLOW

Electron Flow:

- Electrons are repelled by negative end of cell

- Electrons are attracted by positive end of cell

- Electrons move from negative to positive

Conventional Current:

- Flows from positive to negative

- Doesn’t actually happen!!!

- Ben Franklin

8.2 – CIRCUITS EXTENSION

OBJECTIVES

By the end of the lesson you should be able to:

• Distinguish between (and draw) series and parallel circuits

• Calculate current and voltage in all circuits

• Convert between amps and milliamps

TYPES OF CIRCUITS

There are two types of circuits:

1. Series: electrons can only flow along one path

2. Parallel: electrons can flow along more than one path

SERIES CIRCUITS

• Can be recognized because there are no “intersections”

• Current is equal everywhere

IT = I1 = I2 = I3 …

• Voltage is equal to the sum of the voltages of each dry cell

VT = V1 + V2 + V3 …

PARALLEL CIRCUITS

• Can be recognized because there are “intersections” and the

electrons have to make a “choice”

• Current is equal to the sum of the current in each possible

pathway

IT = I1 + I2 + I3 …

• Voltage is equal everywhere

VT = V1 = V2 = V3 …

AMMETERS AND VOLTMETERS

• Ammeters are put into circuits in SERIES

• Voltmeters are put into circuits in PARALLEL

SUMMARY

Series:

• Total voltage is the sum of

the voltage of each dry cell

• Current is the same at

every point in the circuit

Parallel:

• Voltage is the same in

every path

• Total current is the sum of

the current in each path