unit 6 – lecture 2. electricity study of electricity is < 200 yrs old most investigation is in...
TRANSCRIPT
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Unit 6 – Lecture 2
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ElectricityStudy of electricity is <200 yrs old
Most investigation is in last 100 yrs due to modern innovations
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ElectricityElectricity – the flow of electrons
described as an electric currentelectrons flow away from a negative pole
toward a positive pole
electricity can also be described as the forces between charges [why?]
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CircuitsCircuit – a closed path that electric current
followscurrent will stop if the path is no longer
closedvoltage difference must be maintained to
keep current flowing
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BatteriesBattery – provides the voltage difference that
keeps the electric current flowing in a circuithas a positive and a negative terminalalso called a cell
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Circuits
Flow of Electrons
[if circuit is closed]
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Circuits
Battery
Resistance
Bulb
Switch
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Circuit Symbols
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CircuitOpen Circuit – an incomplete or broken
circuitClosed Circuit – a complete, unbroken circuit
Switch – device which opens or closes a circuit
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Practice - Open or Closed?
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Circuits“short circuit” – electrical current finds a
short-cut across the circuit instead of running the way it’s supposed toelectricity jumps across the path of least
resistance - the work is not accomplished
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Circuits
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ReviewOhm’s Law:
Voltage = Current * ResistanceV = I * RVolts = Amps * Ohms
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ReviewIncrease Current Flow by:
greater voltage, more smaller batteries, more conductive metal, shorter-thicker wire, bulb with less resistance
High Resistance = Low CurrentLow Resistance = High Current
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PracticeWhat is the difference between placing a 1.5
battery or a 9v battery in a circuit?
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Types of CircuitsSeries circuit – current has only one path to
followParallel circuit – current may follow more
than one path
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Series CircuitCurrent can only follow one path.Energy into the circuit = Energy used by
circuitIf multiples, add together
power sources [volts]resistors [ohms]
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Series CircuitBulbs:
one bulb = single resistance = full currenttwo bulbs = double resistance = ½ currentthree bulbs = triple resistance = 1/3
current etc…
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PracticeOnce the switch is flipped, which circuit will
have the brighter bulb? Why?
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PracticeOnce the switch is flipped, which circuit will
have the brighter bulb? Why?
In diagram D, if the first bulb blows, what, if anything, will happen to the circuit? Why?
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Parallel CircuitsCurrent has two or more
possible pathseach path is called a branch
Energy into the circuit = Energy used by circuit
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Parallel CircuitsVoltage of the circuit always remains constant
How many volts is the battery putting into the circuit?
What is the voltage across each branch of the below circuit?
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Parallel CircuitsUsing Ohm’s Law [V = I * R], we can
determine the current at each point.
I @ R1 = 9/10 I @ R2 = 9/2 I @ R3 = 9/1 .9 A 4.5 A 9 A
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PracticeOnce the switch is flipped, which circuit will
have the brighter bulbs? Why?
In each diagram, if the first bulb blows, what, if anything, will happen to the circuit? Why?
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AC or DC?AC = alternating current
direction of the current switches back and fort
in the US, most electrical systems have a current that reverses 60 times every second
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AC or DC?DC = direct current
one that flows in a single directiona battery
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Grounding A ground wire is often used for safety
purposes.why? if your refrigerator has a short, the
electricity will flow through the ground instead of through you.