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Chapter 11.3
Electric Current
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D4
Explain the relationship among voltage, current and resistance in a simple series circuit.
Remember:
Stationary electrons =
Moving electrons =
Remember:
Stationary electrons = static electricity
Moving electrons = electrical current
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commiechink.com/. ../static.gif
Circuit –
This is where electrons are moving in a closed and continuous pathway.
There are 3 components to a circuit:
1.Source of electrons
2.Pathway through which to travel
3.Source of energy “push” or “pressure” to move electrons
A
V
Battery
Wire
SwitchResistor(this can be something that uses electricity)
Parts of a circuit
Voltmeter
Ammeter
Bulb
Types of Circuits
Resistors in circuits can be connected in 2 ways
Series Parallel
V3
V1
V2
R3
R1
R2
I
I
I3I2I1
Series Circuits
• The electricity in this type of circuit only has ONE PATH to follow.
• If the circuit is interrupted, the flow of electricity will STOP.
Types of Circuits
Series – resistors lie along a single pathway in the circuit. Amount of current is the same anywhere in the circuit. (same amount of current to do work; work done at the resistors) Resistance is additive. All resistors are affected.
V3
V1
V2
R3
R1
R2
I
Req = R1 + R2 + R3 etc….. Req – resistance equivalent
If resistors are added, all lights would get dimmer.
If resistors were taken away all lights would get brighter.
What would happen if 1 light burnt out? Hint: Each resistor acts like a switch
Parallel Circuit
Parallel Circuits
• The flow of electricity has MORE THAN ONE path to follow.
• If the flow of electricity is disrupted, the electricity may be able to find another pathway
Types of Circuits
Parallel- current flows through many pathways & resistors lie on different pathways. Each pathway only draws the current it needs, the current is split, but the voltage is the same through out.
I
I3I2I1
Sources of energy for electrical current
•Electrochemical Cells – aka “Batteries”
Chemical reactions can be transformed into electrical energy
Chemical Energy Electrical Energy
Wet Cells e.g. car battery
Electrodes – plates made out of: lead (Negative electrode) and
lead oxide (Positive electrode)
Liquid Conductor (Electrolyte Solution) Electrodes are immersed in electrolyte Sulfuric Acid.
www.tiscali.co.uk/.../ images/c00011.jpg
Chemical reaction between lead, lead oxide, and sulfuric acid
release e-s
www.tiscali.co.uk/.../ images/c00011.jpg
Electrons move from negative lead electrode to positive lead oxide electrode
through the sulfuric acid electrolyte
Dry Cells - similar to wet cells, but electrolyte is “Dry” (not water)
e.g. Zinc electrode
Carbon electrode
Ammonium chloride electrolyte
Wires are connected to electrodes to conduct electrons “from” and “back to”
the battery.
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Types of Current
DC – Direct Current, electrons flow in one direction
AC – Alternating Current, electrons flow in one direction first, then in the opposite direction
American homes use AC electricity that changes directions
120 times per second
Current – rate at which electric charge flows through the wire.
Measured by counting the number of electrons passing by a specific point in the circuit in one second.
Current Symbol - Measured in amperes (amps) Amperes Symbol - A
Voltage – amount of electric energy available by potential difference to move electrons.
More Voltage = More Work
Remember (w = f d)
Voltage Symbol - V
Measured in volts - V
Resistance – force opposing the flow of electrons in the current
Good conductors = low resistance
Poor conductors = high resistance
Resistance
Long wires > Short wires
Thin wires > Thick wires
Hot wires > Cool wires
> Means greater
than
Resistance symbol – R
Measured in ohms
Ohms Symbol - (Greek letter omega)
home.att.net/ ~basicelectronics/ohmchart.gif
Born: 16 March 1789 in Erlangen, Bavaria (now Germany)Died: 6 July 1854 in Munich, Bavaria, Germany
http://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Ohm.html
Power Equation
• P = I × V
• Power (watts) = current (A) x voltage (V)
• Watts is the information that you typically associate with a light bulb
Ohm’s Law
I = V/R
V = R
R = V /
I = current
V= voltage
R= resistance
Remember Ohm’s Law V = IR
For a series circuit, since the current is the same throughout the circuit,
then:
V = V1 + V2 + V3 + etc….
V = IR1 + IR2 + IR3 + etc..
V = IReq
Req = R1 + R2 + R3 + etc…
(Req = Resistance equivalent)
I
V
R
V1
V2
V3
R1
R2
R3
- +
V = 12vI
R1
R2
R3
Type of circuit ___________
Req =
I =
R1 = 50
R2 = 100
R3 = 40
- +
V = 12vI
R1
R2
R3
Type of circuit = Series
Req = R1 + R2 + R3
= 50 + 100 + 40
= 190
I = V / Req
= 12v / 190
= 0.063 A R1 = 50
R2 = 100
R3 = 40
Homework
• Read text pp.593-607
• Complete SR pg. 607 #1-4, and 6