Transcript Electricity and Magnetism

Electricity and
Magnetism
Chapters 20 and 21
Electric
charge
•Protons have a positive
charge
•Electrons have a negative
charge
•In most atoms, the
protons equal the
electrons
No net charge
•SI unit is Coulomb (C)
Electric
Forces
•The force of Attraction
or Repulsion
Electric •How the charge affects
Field
the space around it
+
-
•Atoms become charged by
Static
Electricity gaining or losing electrons
•Excess electric charges
on an object transfer to
another object
•Ex: shocking someone by
rubbing electrons off the
carpet.
Lightning
vs.
Thunder
Discharge of static
electricity through
grounding
Easiest way
for e- to move
to the Earth
Result of air expanding
quickly
Rules
1. Law of conservation of
charge
•Not created or destroyed,
just transferred
2. Opposite charges
attract.
3. Like charges repel
Rules
4. Charges produce
electric fields.
Areas of attraction and
repulsion
5. Electrons move more
easily through conductors,
like metals.
Rules
6. Electrons do not move
easily through insulators,
like plastic.
7. Semiconductors: neither
a good conductor or
insulator, like silicon.
Electric
Current
•Flow of charges through a
conductor, usually a wire
•Travels from a high
voltage to a low voltage
•Metric unit  Amperes
•Symbol  I
•2 types: Direct (DC) and
Alternating (AC)
•Opposes the flow of e-
Resistance
•Metric unit  ohms (Ω)
•Depends on length.
Length Resistance
•Depends on temperature.
Temp. Resistance
•Symbol  R
Voltage
•Power of the charge
•Batteries - source
Dry cell
(A, AA,
C, or D)
Wet cell
(car
battery)
•Symbol  V
Ohm’s
Law
•V = I R
Voltage = current x resistance
•Units: Volts, amps, ohms
•Hypothesized resistance
reduces voltage
Electric •A complete path
through which electric
Circuit
charge can flow.
Circuit •Symbols that represent
Diagram the paths that the charges
can flow.
-switches demonstrate
if the circuit is opened
or closed
Series
Circuit
•The current has only one
path to flow through.
•If any part of a series
circuit is disconnected, no
current flows through the
circuit.
Ex. Christmas
Lights
Lightbulb
battery
Parallel •Contains two or more
Circuit paths for current to move
through.
lightbulb
battery
•Ex. Better Christmas lights
Electric •The rate at which
Power electrical energy is
converted to another form
of energy.
•Electrical power is
expressed in watts (W).
•P = I x V
Power = current x voltage
Electric •How much energy that is
Energy used to run appliances
•E = P x t
Energy = power x time
Electric •Correct wiring, fuses,
Safety circuit breakers,
insulation, and grounded
plugs help make electrical
energy safe to use.
•A fuse prevents an
overloaded circuit
•A breaker is a switch
that opens when current is
too high
Magnetic •The force of a magnet
Forces that attracts or repels
•They have 2 strong ends:
north pole and south pole
Magnetic •A magnetic field
(surrounds magnets) can
Field
either attract or repel
other magnets that enter.
Magnetic •The magnetic field that
surrounds the earth is
Field
called a magnetosphere.
•A compass will point
North because it is in align
with the Earth’s magnetic
field
Electro- •The force that usually
magnetic results from charged
particles
Force
•To control this force you
need: *solenoid – a wire
that carries current and
produces a magnetic field
•Changing the current
strengthens the magnetic
field
Devices
•Galvanometer – measures
small amounts of current
*Ex. Fuel Gauge
•Electric Motor – turns an
axle
*Runs a motor
Loudspeakers – contain a
solenoid placed around a
pole of a permanent magnet
•A magnetic field is used to
Electroproduce
an
electric
magnetic
Induction current.
•Voltage is induced in a
conductor by changing
fields in a complete circuit.
Generators
Transformers
•Rotates a coil of wire in a
magnetic field to produce
current.
•2 types: AC and DC
•Change or transform
amounts of voltage by
alternating current
•2 types: step-up and
step-down