17.1
Electric Charge &
Static Electricity
Law of Electric charge-Like charges repel one another while
opposite charges are attracted to one
another.
WHAT ARE THE CHARGES WITHIN AN
ATOM?
Protons = ___ charge
Neutrons = ___ charge
Electrons = ___ charge
Why are protons & electrons
attracted to each other?
Because protons have a positive
charge and electrons have a
negative charge.
They are OPPOSITES!
Why is it important that the electrons
and protons are attracted to each
other?
The attraction keeps the
electrons from flying away from
the nucleus.
Electric Force—force between two
charged objects
Electric Field
The region around a charged object
where a force is exerted on other objects
size of the field depends on
1. amount of charge
2. distance between the charges
If atoms have equal numbers of protons
& electrons how do they become
charged?
- charge = gained electrons
+ charge = lost electrons
OBJECTS BECOME CHARGED BY FRICTION,
CONDUCTION , & INDUCTION.
Friction
Movement of charged particles
when objects have contact and
slide across one another
Conduction
Movement of charged particles
when objects come in direct
contact.
Induction
when charges in an uncharged
metal object are rearranged w/out
direct contact w/the charged
object.
Conservation of Charge
No charges are created or
destroyed, they simply move from
one atom to another.
When an electro-scope is
charged, the metal leaves have
the same charge and repel each
other.
Conductors
A material in which charges can move freely
Insulators
A material in which charges
CANNOT
move freely.
Static Electricity
- Electric charge at rest
- Generally produced by friction or induction
Example—clothes sticking together,
Hair standing up when rubbed on
a balloon
Electric Discharge
The release of electricity stored in a source; ex.—lightning
Balloons and Static Electricity
http://phet.colorado.edu/en/simulation/balloons
John Travolta
http://phet.colorado.edu/en/simulation/travoltage
17.2
Electric Current
The rate at which charges
pass a given point
Expressed in amperes
(amps)
Electrons moving in a wire make up
current and provide energy
to the things that you use each day.
AC
AC = alternating current
Current from outlets
Charges shift from flowing in one direction to
flowing in the reverse direction
In the US most appliances are made to run @
120 V
DC
DC = direct current
Current from batteries
Always flows in the same direction
Voltage
• The amount of energy released as
a charge moves between two
points in the path of a circuit
• Expressed in volts = V
• The higher the voltage is, the
more energy is
released per charge
Batteries are made with various voltages
for use in many different devices.
Resistance
• Electrical friction
• Expressed in ohms (Ώ) or R
(equations)
• the higher the resistance is,
the lower the current
• Depends on the object’s
material, thickness, length, &
temp.
Resistance
Good conductors have lower resistance,
ex., Cu
Poor conductors have higher resistance,
ex., Fe
Superconductors
- can repel magnets
One interesting property of superconductors is that they
repel magnets. The superconductor in this photo is
repelling the magnet so strongly that the magnet is
floating.
Generating Electrical Energy
Cells- change chemical or
radiant energy into electrical
energy (batteries are cells too)
Convert chemical energy into
electrical energy
This cell uses the juice of a lemon as an
electrolyte and uses strips of zinc and
copper as electrodes.
Thermocouples
Convert thermal energy into
electrical energy
In a simple
thermocouple,
one section of
the loop is
heated and one
section is
cooled.
Photocell
Light energy converted into
electrical energy
Solar energy is converted
with this
Circuits
17.4
Parts of a Circuit
1.
Energy source
2.
Wires
3.
Load
SWITCHES
closed
opened
TYPES OF CIRCUITS
1. SERIES:
•
all parts are connected in a single loop
• if one part stops working—it all stops; bulbs get
dimmer as more bulbs are added
Uses: burglar alarms
CIRCUITS
2. PARALLEL
•
loads are connected side by side;
• charges have more than one path to follow;
• loads use the same voltage
USES: Christmas tree lights, house wiring
CIRCUIT FAILURE
CAUSES:
1. Broken wires
2. Water
3. Overloaded
FUSES
CONTAIN A METAL STRIP THAT
MELTS WHEN CURRENT GETS
TOO HIGH
CIRCUIT BREAKERS
• Metal in breaker warms, bends, opens
switch, stops flow of current
• GFCI (ground fault circuit interrupter)-
•
if the current on either side of the
outlet differs the charges stop flowing
ELECTRICAL SAFETY TIPS
1.
Make sure the insulation on cords is not worn
2.
Do not overload circuits by plugging in too many electrical devices
3.
Do not use electrical devices while your hands are wet or while you
are standing in water
4.
Never put objects other than a plug into electrical outlet