Transcript current1 - Cobb Learning

What did we just finish studying?
_________: the buildup of electric charges on objects.
What are we studying next?
___________: the flow of charges along a conductor.
Current (Definition formula): how fast do the
charges flow?
I = ________ unit: _____
q
I
t
t = _______ unit: ______
It’s work to go that
way! 
e-
0V
Ohm’s Law: (Relationship formula.)
Rearranging to I  V
R
written V=IR
1.The size of the voltage difference.
• 1V: e-
I could use some time
alone.
• 10,000V: e-
@#$%! Get me out of
here!.
q = ________ unit: _____
What makes the charges want to flow anyway?
__________: aka ______ _______. A difference in
the voltage at each end of a wire (“across” the wire)
10V
So, charges flow because of potential difference (the
energy to escape crowded electron areas) What
determines how fast they flow?
V  IR
2. Resistance: obstacles in their path
• Wire thickness. Thin = _____
• Wire temperature. Hot = _____
• Wire material conductivity. Good conductor =_____
• Wire length. Long = ______
Electric
Current
is more meaningful, but it’s usually
Ohm’s law means: Current is directly related to voltage: (more
push, more flow) but indirectly related to resistance (more difficult
path, less flow).
Electrical Power: It was a dark and stormy night.
Lightning flashes. The lights go black. ‘Oh no!’’ you cry, ‘the
power is out!’
What is (electrical) power anyway? It’s the energy per second
supplied when there is a current.
How does electrical energy travel?
V = _______ unit______
•
I= _______ unit:_______
R= _______unit:_______
Way faster than the electrons do (nearly speed of
light vs. cm/min)
•
As a wave in the electric and magnetic fields around
the charges
How much current flows through a circuit with 8 ohms of
resistance and a potential difference of 120V?
•
Outside the wires
V = IR
Power: amount of energy transmitted over time.
Definition formula:
P= ____________unit: ___
Energy
P
t
Energy:________ unit:____
t= _________
unit:____
Relationship formulas: power is related to current,
resistance and voltage, which gives us three new
formulas!
V2
2
P  IV  I R 
R
Your hair dryer uses 5 amperes when on the high
setting. Its resistance is 24 ohms. How much power
does your hair dryer draw?
Power Plants and $:
Georgia Power charges you how much? About ________.
What is a kWh? A unit of __________ equal to you, using
__________ for _________
C= _________ unit_______
r= _________ unit________
C  rPt
P= _________ unit_______
t= __________ unit_______
You left your 350 W TV on all night from 4 p.m. to 8:30
a.m. Your mother tells you to pay for the power it used.
Your power costs $0.10/kWh. How much will it be?
Power
and circuits
Circuits: a closed path made up of wires, a “pump” and
resistors.
•Pump = source of voltage: “cells,” batteries, generator,
power plant
•Resistor = thing using electricity: lamp, TV, dryer
•DC current: Electrons move from + terminal to –
terminal (what we think of as normal =batteries)
•AC current: Electrons dance back and forth and don’t
progress forward (electricity from the wall)
•Energy moves from the pump to the resistor outside the
wires in both directions as a wave in the electric field.
Series Circuits
•
only one path for the current
to flow through
•
if one resistor burns out, the
entire circuit is “open” and
stops working.
•
same current through every resistor
Parallel Circuits:
•
more than one path for
current to flow through
•
if one resistor burns out,
only one path is “open” so circuit still works
•
same voltage across every resistor
Circuit Schematics and Ohm’s Law Charts:
Draw a series circuit and Ohm’s law chart for:
Draw a circuit with:
•9V battery
•9V battery
•2 resistors in series, 5Ω and 13 Ω
•R1 = 5Ω
I = ____A
Rules:
•Resistor is a zigzag, labeled R1 = ___Ω
More Rules:
• resistors in series make one path.
•In series: Current is the same!
•Label R1, R2 etc.
•Fill in chart using V=IR for and series formulas for
Draw a parallel circuit an Ohm’s law chart for:
Draw a series circuit an Ohm’s law chart for:
•9V battery
•2 resistors in parallel, 5Ω and 13 Ω
•12V battery
•Series: R1= 6Ω, R2=3 Ω
•1 breaker for ______ A
•Voltmeter around R1
•Ammeter
•Battery (multiple “cells”) is labeled with the V, is on left, + line
is long and on top, - line is short and down.
•Wires in rectangle shape
•1 fuse for _______ A
More Rules:
• Breaker symbol is
More Rules:
• resistors in parallel make many paths
•In parallel: Voltage is the same!
•Fill in chart using V=IR for and series formulas for
•Fuse symbol is
.You decide current from chart
•Voltmeter symbol is
.
It measures _______ difference. Wire
voltmeters in __________ around the resistor
because it measures the difference.
•Ammeter symbol is
. Ammeters
measure ________. Wire is ________ with the
circuit because it measures electron flow.