Download Circuits - Fulton County Schools

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
Switch
Bulb
Battery
Resistance
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.
 I @ R1 = 9/10
.9 A
I @ R2 = 9/2
4.5 A
I @ R3 = 9/1
9A
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.