Download Current Electricity

CURRENT ELECTRICITY
Current Electricity
• Current Electricity is the
flow of electrons
• Electrons are moving, so
what kind of energy do
they have?
• As the electrons move through the
material in the circuit, they collide
with the atoms in the material. So
energy is passed on.
Current vs. Static Electricity
• Static Electricity
• Current Electricity
– Build up and
discharge of all e-,
due to forces of
charges
– Continuous flow of
electrons, due to
electric force of
charges
Examples: Lightning,
getting shocked, etc.
Examples: light bulbs,
cell phones, etc.
Electric Circuits
Resistance
Wire
Battery (Source)
Circuit is a
complete path
for electrons to
flow along wires
connected to a
source
Types of Circuits
• Series Circuits
– One path for the
electrons to flow.
– If one part of the circuit goes
out, all other parts go out as
well
• Parallel Circuits
– Multiple paths for the
electrons to flow.
– If one part of the circuit goes
out, the other parts are not
affected
Series Circuit
• Disadvantage: if there
is a break anywhere
in the circuit, the
entire circuit is open
and no current can
flow
• EX: Christmas tree
lights
Parallel Circuit
• If there is a break in
one branch, the
electrons and current
can still flow through
the other branches
• EX: more expensive
Christmas tree lights
Types of Circuits
• Identify the following as series or parallel.
Series
Parallel
Parallel
Series
•
Current Electricity – parts of a
circuit
Resistance
– Material that gets in the way of the electrons, slowing
them down. (the lightbulbs, etc.)
– Unit: Ohm Ω
• Current
– Amount of electrons flowing through circuit.
– Unit: Ampere (A)
• Voltage (Potential Difference)
• Amount of charge build up and separation
– Unit: Volt (V)
CIRCUIT LAB
• You will be working in groups of 4, but each
person will have their own lab sheet (purple)
• Be gentle with equipment. Come get a hand
generator from me when you reach that part of
your lab.
• When you are done with the lab, I will have a set
of series and parallel circuits on the overhead.
See if you can make them all.
Ohm’s Law
Current vs Resistance
– As more “stuff”
(resistance) gets in the
way, there will be less
flowing electrons
(current)
– As there is more
charge build up and
separation (Voltage),
there can be more
electron flow
Current (Amperes)
• Ohm’s Law
30
25
20
15
10
5
0
0
5
10
Resistance (Ohms)
15
Ohm’s Law
• V= I*R
• Voltage = Current * Resistance
Practice Problem 1
• Calculate the voltage in a circuit
with a resistance of 25  if the
current in the circuit is 0.5 A.
V= I*R
Practice Problem 2
• A current of 0.5 A flows in a 60W light bulb when the voltage
between the ends of the
filament is 120 V. What is the
resistance of the filament?
• V= I*R or I = V
R
Electric Power
• The rate at which electric energy
does work or provides energy
(how quickly it pushes charges
through a circuit)
• Power = Voltage x Current
• P=V*I
• SI Unit for Power is Watts (W)
You’ve heard of Kilowatts-large amounts like in the
home
Practice Problem 3
• A toaster oven is plugged into an
outlet that provides a voltage
difference of 120 V. What power
does the oven use if the current
is 10 A?
• P = V*I
Practice Problem 4
Calculate the current flowing into
a desktop computer plugged
into a 120-V outlet if the power
used is 180 W.
• P = V*I
Ohm’s Law Practice
Physics to Go: P. 461 #’s 1,2,3,5,6
Physics to Go: P. 469 #’s 4,5,6, 8-13
Electrical Energy
• Electric companies charge a
certain amt for electricity
• The bill is based on how much
energy is used in the household
• Electric meter records this
amount of energy
Electrical Energy (kWh)
Problems
• Energy = Power x Time
•E=Pxt
• Energy (kilowatt-hours or kWh)
• Power (kilowatts)
• Time (hours)
Practice Problem 1
• A microwave uses 1,200 W for
0.25 hr. How much electrical
energy is used by the
microwave?
• E = Pt
• or
• kWh = P x hrs/1000
Practice Problem 2
• A refrigerator operates on average
for 10.0 h a day. If the power rating
of the refrigerator is 700 W, how
much electrical energy does the
refrigerator use in one day?
• E = Pt
• or
• kWh = P x hrs/1000
Practice Problem 3
• A TV with a power rating of 200
W uses 0.8 kWh in one day. For
how many hours was the TV on
during this day?
• E = Pt
• Or
• kWh = P x hrs/1000
Practice Problem 4
• Suppose electricity costs $0.08
per kilowatt-hour. How much
would it cost to run a 100-watt
light bulb for 5 hours?
• E = Pt x cost
• kWh = P x hrs x cost/1000
Practice Problem 5
• Calculate the monthly cost of
using a 700-W refrigerator that
runs for 10 h a day if the cost
per kWh is $0.09.
• E = Pt x cost
• kWh = P x hrs x cost/1000
Electrical Safety
1. Never handle electrical
appliances if your hands are
wet or you are standing in
water.
2. Never run wires under carpets.
3. Never overload a circuit by
attaching too many appliances
to it.
Electrical Safety
4. Always repair worn or frayed
wires to avoid short circuits.
1. Never stick your finger in an
electric socket or a utensil in
an appliance that is plugged in.
2. Never touch wires that have
come loose from power poles
or bldgs.