Electricity and Magnetism
Spring Final Exam Review
2003
Circuit diagrams
E A shorthand
method of drawing
a real circuit
E Make sure you
know each part’s
symbol
Types of circuits
E Open - a break in
the path, no
current flows
E Closed - no
breaks in the
path, current
flows
Static electricity
E Electric charge build up on an object
E like
charges
repel
E unlike charges attract
Electroscope
E An instrument used to detect charged
objects
Voltage
E The measure of energy level at any point in
a circuit
E leaves the positive end of the battery with
energy (high voltage), returns to the
negative end with no energy (low voltage)
E voltage is reduced in a circuit when energy
is used - light bulbs, resistors, appliances
Current
E The flow of electric charges
E Two types
•
•
AC - alternating
DC - direct
E circuit breakers control the flow of current
and shut off when too much is flowing at
once
Resistance
E How easily charges can move through an
object
•
•
•
conductor
insulator
semi-conductor
Resistance vs. current
E High resistance, low current
E Low resistance, high current
Ohm’s Law
V
I
R
Ohm’s Law example
Find the resistance of a portable lantern that
uses a 24 V power supply and draws a
current of 0.80 amperes.
E V = IR
E 24 V = (0.80 amperes)(R)
E R = 30 Ohms
Electrical power
P
V
E The rate at which energy is flowing
E measured in watts (Joules/second)
I
Power example
E An electric space heater requires 29 A of
120 V current to adequately warm a room.
What is the power rating of the heater?
E P = IV
E P = (29 amp)(120 v)
E P = 3480 watts
Types of circuits
Series
E
E
One path
Add individual
resistors to get total
resistance in circuit
Parallel
E
E
More than one path
Look at different paths
for resistance
Kirchoff’s Voltage Law (series)
E Around any closed circuit, all the voltage
changes must add up to zero.
Kirchoff’s Current Law (parallel)
E The current flowing into a branching point
in a circuit must flow out again.
Magnetism
E The ability to make forces on magnets or
other magnetic materials
E all have two opposite poles - N and S
E unlike poles attract
E like poles repel
E lodestone and magnetite are natural
magnets
Electromagnet
E
E
E
A magnet created
by the flow of
electric current
More current =
stronger
electromagnet
uses: levitated
train, toaster,
doorbell
The right hand rule
E When your fingers
curl in the
direction the
current is flowing,
your thumb points
toward the
magnet’s North
pole.