Download Classifying Matter and the Periodic Table

0016: Electricity and Magnetism
1. recognize the characteristics of static electricity
Electricity describes charged particles
• Rub a balloon with wool,
picks up electrons
• Rub glass with silk, loses
electrons
• Objects attract or repel
when “electrically charged”
• “static electricity”
Figure 5-1
The two kinds of electrical charges. Opposite charges
attract, while like charges repel.
Electricity describes charged particles
• These charged particles can be at rest
(“static electricity”)
• or they may be moving
(“current electricity”)
Coulomb’s Law
• The electric force between two charged
particles varies directly as the product of
their charges and inversely as the square
of the separation distances.
• force (newtons) = k x 1st charge x 2nd charge / distance2
Electrical Field
• A kind of “aura” or “force field” around
every electric charge
• Extends radially away
from the proton and
in opposite direction
about the electron.
…distinguish between
conductors and insulators
• Conductors
• Insulators
• Material that electrons • Material that electrons
are able to pass
do not through easily
through
• Glass, wood, rubber,
• Metals, ionic
plastics
solutions
0016: Electricity and Magnetism
2. demonstrate knowledge of the components of an electric
circuit and their functions.
Electrical potential and electric current
• Movement of electric charge creates
electric current
• Charges move as current only when energy
is supplied to them
• Circuit
• Switch
• Voltage
• Current
If we use the water analogy…
• Voltage = the pressure
• Current = the rate of flow
Voltage
•
•
•
•
•
The push that makes electrons move.
1.5 V “D” cell or 6 V lantern battery
Higher voltage = greater push on electrons
Water analogy
Voltage causes current.
Electric Current
• Voltage creates current
• Current is the amount of charge
passing a point in a circuit in a
second
• Metric unit = Ampere (A)
• Measures by an ammeter
• Different devices often carry
different amounts of current
…distinguish between
DC
and
AC
• Direct current
• Current moves in one
direction
• From dry cells or
batteries
• Alternating current
• Pumped to us by
Cobb EMC
• Oscillates back and
forth at 60 Hz
• wall sockets
Ohm’s Law
• How is current related to voltage?
• Direct relation between the two led to
discovery of “resistance”
• Voltage / Current = Resistance (V / I = R)
Resistance
• measures how hard it is for current to
move through a conductor (unit =
Ohm).
• Easier for electrons to move through
thick wires than thin wires
• Light bulb filament, thin, high
resistance, heats up and glows
0016: Electricity and Magnetism
3. compare series and parallel circuits.
…distinguish between
Series Circuits & Parallel Circuits
• Only one path for
current flow
• Same amount of
current thru entire
circuit
• Cheap string of
decorative lights
• Alternate paths for
current flow
• Current divides up
among the paths
• Wiring system for
lights and elec outlets
in homes & buildings
Electrical Safety
•
•
•
•
Fuses
Circuit breakers
Ground-fault interrupter
“Atoms Family” ElecSafety link
Electric Power
• Power = energy used / time
• Also calculated as product of current and
voltage
• Watts = amp’s x volts
• Ex: 60W bulb draws .5 A on a 120V line
120W lamp draws 1A on a 120V line
 If a 120V line to a socket is limited (by a
fuse) to 15A, will it operate a 1200W dryer?
0016: Electricity and Magnetism
4. identify properties of magnets and characteristics of
magnetic fields.
Magnetism
• Children are
fascinated by
magnets!
• “floating” paper clip
• “jumping” nails
• “iron filing” cartoon
hair
The little fridge magnet reminds us that the
magnetic force on Earth is stronger than gravity.
magnetism
• Magnesia, province
of Greece
• Unusual property of
lodestone noted over
2000 years ago
th
12
C, Magnets first used in
navigational compass, Chinese
16th C, William Gilbert
• “Every magnet has
two poles, a north
and a south.”
• “Like magnetic poles
repel, unlike poles
attract.”
Figure 5-3
A compass needle and the Earth. Any magnet will twist
because of the forces between its poles and and those of
the Earth. Every magnet has at least two poles.
Courtesy Andy Washnik
Figure 5-5(b)
Iron filings placed near a bar magnet align themselves along
the field.
Figure 5-4
A magnetic field. Small magnets placed near a large one orient
themselves along the lines of the magnetic field, as shown.
Figure 5-5(a)
A bar magnet and its magnetic dipole field.
“Opposites attract. Likes repel.”
The above describes both
magnetic and electric
force, but
electric charges can
be isolated,
magnetic poles
cannot.
Figure 5-6
Cut magnets. If you break a dipole magnet in two, you get two
smaller dipole magnets, not an isolated north or south pole.
0016: Electricity and Magnetism
5. demonstrate knowledge of the relationship between
moving electric charges and magnetic fields and applications
of electromagnets in everyday life (e.g., motors, generators)
1820, Hans Oersted
• …connected a
battery to let
electric current
flow, and noticed a
compass needle
twitch and move.
Electricity & Magnetism:
“ two sides of the same coin “
• Every time an electric
charge moves, a
• Every time a magnetic
magnetic field is
field varies, an electric
created.
field is created.
• (electromagnet)
• (hydroelectic dams)
Electric motors convert electricity into
magnetic fields, for useful rotary motion
Figure 5-8
An electric motor. The simplest motors work by placing an
electromagnet that can rotate between two permanent magnets.
(a) When the current is turned on, the north and south poles of the
electromagnet are attracted to the south and north poles of the
permanent magnets. (b)–(d) As the electromagnet rotates, the
current direction is switched, causing the electromagnet to continue
rotating.
Electric motors convert electricity into
magnetic fields, for useful rotary motion
Electrical Generators
• …are the exact
opposite of
electric motors:
they convert
rotary motion
into electrical
energy.
link
Energy Transformation - kinetic energy of moving
water can be used to turn a wheel that runs the mill to grind
grain.
Energy Transformation
Wind can be used to vary a magnetic field about
wires, to generate alternating current.
We can burn coal to heat water to produce steam to
turn a turbine to vary a magnetic field about wires,
to generate alternating current. (coal-fired power
plant)
We can dam rivers, then release energy from the
lake side, to turn a turbine, to vary a magnetic field
about wires, to generate alternating current.
(hydroelectric energy)
We control nuclear fission reactions to heat water to
produce steam to turn a turbine to vary a magnetic
field about wires, to generate alternating current.
(nuclear energy)
In some parts of the world, we can use heat from
the Earth to produce steam to turn a turbine to vary
a magnetic field about wires, to generate alternating
current. (geothermal energy)
Anything that can turn an axle can
power a generator.
• Flowing water, pressurized steam, wind, or
a gasoline engine can drive a rotating
turbine that houses coils of copper wire.