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.