Unit 6 – Lecture 2

Electricity Study of electricity is < 200 yrs old Most investigation is in last 100 yrs due to modern innovations

Electricity Electricity – the flow of electrons described as an electric current electrons flow away from a negative pole toward a positive pole electricity can also be described as the forces between charges [why?]

Circuits Circuit – a closed path that electric current follows current will stop if the path is no longer closed voltage difference must be maintained to keep current flowing

Batteries Battery – provides the voltage difference that keeps the electric current flowing in a circuit has a positive and a negative terminal also called a cell

Circuits Flow of Electrons [if circuit is closed]

Circuits Battery Resistance Bulb Switch

Circuit Symbols

Circuit Open Circuit – an incomplete or broken circuit Closed 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 to electricity jumps across the path of least resistance - the work is not accomplished

Circuits

Review Ohm’s Law: Voltage = Current * Resistance V = I * R Volts = Amps * Ohms

Review Increase Current Flow by: greater voltage, more smaller batteries, more conductive metal, shorter-thicker wire, bulb with less resistance High Resistance = Low Current Low Resistance = High Current

Practice What is the difference between placing a 1.5 battery or a 9v battery in a circuit?

Types of Circuits Series circuit – current has only one path to follow Parallel circuit – current may follow more than one path

Series Circuit Current can only follow one path. Energy into the circuit = Energy used by circuit If multiples, add together power sources [volts] resistors [ohms]

Series Circuit Bulbs: one bulb = single resistance = full current two bulbs = double resistance = ½ current three bulbs = triple resistance = 1/3 current etc…

Practice Once the switch is flipped, which circuit will have the brighter bulb? Why?

Practice Once 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 Circuits Current has two or more possible paths each path is called a branch Energy into the circuit = Energy used by circuit

Parallel Circuits Voltage 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 Circuits Using Ohm’s Law [V = I * R], we can determine the current at each point. R1 = R2 = R3 = 9/1.9 A 4.5 A 9 A

Practice Once 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 direction a 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.