unit 6 – lecture 2. electricity study of electricity is < 200 yrs old most investigation is in...
TRANSCRIPT
Unit 6 – Lecture 2
ElectricityStudy of electricity is <200 yrs old
Most investigation is in last 100 yrs due to modern innovations
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?]
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
BatteriesBattery – provides the voltage difference that
keeps the electric current flowing in a circuithas a positive and a negative terminalalso called a cell
Circuits
Flow of Electrons
[if circuit is closed]
Circuits
Battery
Resistance
Bulb
Switch
Circuit Symbols
CircuitOpen Circuit – an incomplete or broken
circuitClosed Circuit – a complete, unbroken circuit
Switch – device which opens or closes a circuit
Practice - Open or Closed?
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
Circuits
ReviewOhm’s Law:
Voltage = Current * ResistanceV = I * RVolts = Amps * Ohms
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
PracticeWhat is the difference between placing a 1.5
battery or a 9v battery in a circuit?
Types of CircuitsSeries circuit – current has only one path to
followParallel circuit – current may follow more
than one path
Series CircuitCurrent can only follow one path.Energy into the circuit = Energy used by
circuitIf multiples, add together
power sources [volts]resistors [ohms]
Series CircuitBulbs:
one bulb = single resistance = full currenttwo bulbs = double resistance = ½ currentthree bulbs = triple resistance = 1/3
current etc…
PracticeOnce the switch is flipped, which circuit will
have the brighter bulb? Why?
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?
Parallel CircuitsCurrent has two or more
possible pathseach path is called a branch
Energy into the circuit = Energy used by circuit
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?
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
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?
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
AC or DC?DC = direct current
one that flows in a single directiona battery
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.