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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