Transcript Physical Science Goal 3 Notes

Physical Science
Goal 4 Notes
Brain Pop: Electricity
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Electricity
 Static
electricity is the
build up of an electrical
charge.
 For
electrically charged
materials, opposites
charges attract, while
like charges repel.
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chapter20/concepts_in_motion.html
Electricity
• Electricity is moving electrons.
 Conductors
allow electrons to move freely
through them.

Objects are grounded when they are
connected to the earth or ground by a good
conductor.
 Insulators
are materials that do not allow
electrons to move freely through them.
Voltage – Potential Difference
 The
electrical potential is the potential
energy difference per unit charge.
 The
potential difference is the difference in
potential between two places.

Units for potential difference are volts (V).
Electrical Potential Difference
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chapter21/concepts_in_motion.html
 Potential
difference can be referred to as
voltage and is measured with a voltmeter.
 Voltage
is a comparison of the energy
carried by electrons at different points.
Circuit
 Circuit
is a closed path through which
electrons flow.
 Current
is the flow of electrons through a
wire or conductor.

Units for current are amperes (A) as is a
measure of the number of electrons passing a
point in a given time.
Batteries
A. Dry cell - Electron pump
with a potential difference
between the positive and
negative terminals.
•
Zinc container with a moist
chemical paste with a solid
carbon rod in the center.
The paste contains MnO2
(manganese dioxide),
NH4Cl (ammonium
chloride) and C (carbon)
which reacts with the zinc.
B. Wet cell - Contain metal
plates placed in a
chemical solution
(electrolyte).
Ex.: Car battery – lead
storage battery. Plates
of lead (Pb) and lead
dioxide (PbO2) in
sulfuric acid (H2SO4)
solution. The car
battery has 6 cells with
a potential of 2 V each
for a total of 12 V.
Resistance


Resistance is a
materials ability to
oppose the flow of
electrons causing it to
change electrical energy
into thermal energy and
in some cases light.
Copper - low resistance
Resistance is measured
in ohms (Ω).
Tungsten - high resistance
 All
conductors, except superconductors at
very low temperatures, have some
resistance.
 For
a given material, resistance is
increased as length increases; decreases
as thickness increases; and, usually
increases as temperature increases.
Ohm’s Law
Potential difference = current X resistance
V= IR
Units
V = potential difference
volts (V)
I = current
amperes (A)
R = resistance
ohms (Ω)
Resistance and Ohm’s Law
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chapter22/concepts_in_motion.html
• Voltage increases when current
increases.
• Voltage decreases when resistance
increases
Flash Card
V = R
V

R
Ohm's Law
V - voltage
I - current
R - resistance
Units
V (volts)
A (amperes)

(ohms)
Circuits
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hill.com/sites/0078807220/student_view0/
chapter22/concepts_in_motion.html
Circuits
1. Series circuit – only one path for the
electricity
2. Parallel circuit – More than one path for
the electricity with each branch having
the same potential difference.
3. Complex circuit – contains both series
circuits and parallel circuits
 Series
Circuits
 Parallel
Circuits
3. Open circuit – when a switch is opened
(turned off) or a bulb burns out the current
no longer flows through that path,
therefore the circuit is open.
4. Closed circuit – when a switch is closed
(turned on) and bulbs burn the current
flows through the path (s), therefore the
circuit is closed.
Safety Devices
 Fuses
and circuit breakers are safety devices
to prevent a circuit from overheating and
causing a fire.
 Fuses
have a metal strip that melts when the
circuit gets too hot, causing the circuit to
open.


Fuses can only be used once and must be
replaced with the same size and type of fuse.
Fuses can explode if they get too hot and cause
fires.
Fuses
Breakers
 Circuit
breakers contain a metal strip that
bends as it heats up and trips the breaker
switch to open the circuit.


Breakers can be reset several times before
they have to be replaced.
Like fuses breakers come in different sizes.
 Main
breakers control the flow of electricity
into the house.

When they are thrown (or tripped) there will
be no electricity in the house or building.
Breakers
Electrical Power
Electrical power is the rate at which electric energy
is converted into another form of energy.
Electric Power = current X voltage
PE = I V
Units
PE = electric power
watts (W) or kW
I = current
amperes (A)
V = voltage
volts (V)
One watt of electric power is produced when
one ampere of current flows through a circuit
with a potential difference of one volt.
Flash Card
PE = I V
PE

V
Electrical Power
PE - electrical power
Units
W (watts)
I - current
A (amperes)
V - voltage
V (volts)
Electrical Energy
Electrical Energy is calculated by multiplying the
electrical power by the amount of time the power
was used.
Energy = power X time
E=Pt
Units
E = electrical energy
kilowatt-hours (kWh)
P = electrical power
kilowatt (kW)
t = time
hours (h)
One kilowatt-hour (kWh) is 1000 watts of
power used in one hour.
Flash Card
E= Pt
E
P
t
Electrical Energy
Units
E - Electrical energy
kWh
P - electrical power
kW
t - time
h
Electricity
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Brain Pop: Magnetism
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Magnets
point north – south when
suspended from a string and align with the
Earth’s magnetic north and south poles.
 Magnets
 Magnetism
is a force of attraction and
repulsion between like and unlike poles.
 Magnetic
poles are at the ends and are
the area of strongest attraction.
 Permanent
magnets retain their properties
for a long time and are made of iron (Fe),
nickel (Ni) or cobalt (Co).


Magnetite is a mineral with natural magnetic
properties.
Lodestone is a natural magnet.
 Magnetism
can be conducted through paper
clips and nails to make temporary magnets.

Temporary magnets lose the magnetic properties
after being removed from the magnet.
Magnetic Fields
Magnetic field is the area around a magnet
where the magnetic forces act.
 They
 The
are strongest near the poles.
Earth’s magnetic north pole is near
the south pole and the Earth’s magnetic
south pole is near the north pole.
Magnetic Domains
 In
order to form a magnet, the magnetic
poles of the atoms must align.
 Magnetic
domains are groups of atoms
with aligned magnetic poles.


Permanent magnets can lose their domains if
heated or dropped.
When a permanent magnet is cut into smaller
pieces, each piece will have its own poles.
 Compass
is an instrument for determining
direction that contains a magnetized
needle to point to the Earth’s magnetic
poles.
 1820,
Hans Christian Oersted, Danish
physics teacher, observed that current
passing through a wire produced a
magnetic field that could be detected by a
compass, and that the direction of the
magnetic field reversed when the direction
of the electric current reversed.
Electromagnets
Electromagnets are strong temporary magnets
produced by inserting an iron core into a coil
of wire and passing an electric current
through the wire.
 Strength of electromagnets can be changed
by changing the number of coils in the wire
or the amount of current going through the
wire.
 Uses for electromagnets: loudspeaker,
doorbells, lifting metal objects, meters, toys,
and motors.
Galvanometers
 Galvanometer
is an instrument used to
detect electrical current.


Ammeter is a galvanometer that measures
current and is connected in series in the
circuit.
Voltmeter is a galvanometer that measures
potential difference and is connected in
parallel in the circuit.
Electromagnetic induction
 1831,
Michael Faraday, British scientist,
and Joseph Henry, American scientist,
working independently found that by
moving a wire in and out of a magnetic
field that they could produce an electric
current.

Electromagnetic induction is the production of
an electrical current by moving a wire through
a magnetic field.
Generators
Generators produce electricity by rotating a
loop of wire in a magnetic field.
 The wire loop is rotated by a mechanical
energy source.
 This produces alternating current because
the current changes direction each time
the wire passes a different pole.
 Turbines
are large wheels that rotate when
pushed by water, wind, or steam.
 The
steam can be produced by burning of
fossil fuels or nuclear reactions.
Types of Current
 DC
– direct current flows in one direction
– alternating current reverses the
direction of flow in a regular pattern
 AC

In the US, our current has a frequency of 60
Hz and changes direction 120 times/sec.
Transformers
Transformers reduce or increase voltage of
alternating current.
Transformers contain 2 coils of wire (primary
coil – incoming current and secondary coil
– outgoing current) wrapped around an
iron core.
2 Types of Transformers
 Step-up
transformers have more coils of
wire on the secondary coil and increase
the voltage.
 Step-down
transformers have more coils
of wire on the primary coil and decrease
the voltage.
Superconductors
 1911,
Heike Kamerlingh Onnes, a Danish
physicist, discovered that at low
temperatures some materials lose their
electrical resistance.
 Since
the material loses its electrical
resistance at low temperatures it is called
a superconductor.
 The
temperature at which the
superconductor loses its electrical
resistance is its critical temperature.
 Most
of these temperatures are near
absolute zero -273 °C.
 Liquid
helium (4.2 K or -268.2 °C) was
used to cool the first superconductors.
 1987,
J.G.Bednorz and K.A.Müller
produced a superconductor from a
ceramic material with a critical
temperature of 30 K (-243 °C).
 We
now have superconductors with critical
temperatures at 130 K (-143 °C) and use
liquid nitrogen (-196 °C) to cool the
material because it is cheaper.
 Superconductors
are more efficient
because they do not lose energy due to
resistance.
 Research
continues to build
superconductor that is less brittle and
more flexible and thinner.
Floating trains: Fact or Fiction?
 Using
superconductors for the rails and
magnet in the bottom of the train can
cause the train to levitate (float) above the
rails.


+ No Friction, No Pollution, Reduced Energy
Waste
Air resistance still exist, Environment can still
have an effect.