Transcript Multimeter Instructions - Fox Valley Lutheran High School

ELECTRICITY
Chapter 13.2 – 13.3
VOLTAGE / AMPERAGE /
WIRE / BATTERY / SERIES /
PARALLEL / MULTIMETER
VOLTAGE – page 438-439
• An electric charge has potential
electrical energy.
• The unit for measuring potential
electrical energy is the volt.
• A common source of potential energy
is a battery.
• A battery converts chemical energy
into electrical energy.
• A voltage that sets charges in motion
may commonly range from 1.5 – 24
volts in batteries.
• Voltages are much higher in electrical
outlets.
AMPERAGE – page 439
• Electrical current is the movement
of electricity from one location to
another usually through wires.
• It is due to the movement of a
charge from a place of high
potential to one of low potential.
• An ampere (amp) is the measure of
the amount of current flowing
through a circuit. It is the rate that
electric charges move through a
conductor.
OHM – page 441-445
• An OHM is a measure of the resistance (friction) in a
circuit.
• Some things that resist the flow of electricity are:
– Thin wire (dimmer light bulbs – thin wire does not let as many
electrons flow through the wire so the light is not as bright)
– Some types of metals (tungsten in light bulbs)
– High temperature (as a circuit heats up it creates more
resistance!)
• Resistance produces HEAT and if there is enough heat it
produces LIGHT.
OHM /AMPERE / VOLT –
The relationship between these
can be calculated using :
• ohms = volts
amperes
• Materials with low resistance are called
conductors.
• Materials with high resistance are called
resistors or insulators (depending on how used)
• Superconductors are materials that have zero
resistance below a certain temperature.
• Semiconductors are materials with electrical
properties between conductors and insulators.
WIRE CHARACTERISTICS
• SIZE
– Thickness determines how easily electricity can flow in a
circuit.
• MATERIAL
– Some metals are better conductors than others.
– Most home and auto wiring is COPPER
– Some electronics may be gold or silver
• INSULATED / NOT INSULATED
– Bare wire…no insulation
– Plastic or rubber covered wire
– Varnish covered used in motors and electromagnets.
BATTERY CHARACTERISTICS
• Size
– Depends on application and power needs.
• Voltage
– Does not depend on size…may be large
or small
• Amperage
– Depends on size…larger = more amps
• Materials – determine strength,
longevity, charge ability.
–
–
–
–
Carbon zinc
Nickel-cadmium
Silver oxide
Lithium
13.3 CIRCUITS SERIES CIRCUIT
• A SERIES CIRCUIT has only one path for the current
to travel. All the current must go through each part of
the circuit.
• A major problem with this is that if one part of the
circuit is broken (burned out bulb etc.) the whole circuit
goes dead.
• Also the resistance keeps increasing as the circuit
gets larger. This means that as bulbs are added to a
series circuit they do not burn as brightly as when
there are fewer bulbs.
PARALLEL
CIRCUIT
• A PARALLEL CIRCUIT has separate paths for
the current to flow.
• If the current in one path is broken, the current
can still flow in the other paths. If one bulb
burns out, the rest remain on.
• Resistance is not affected by how many bulbs
are in the circuit. Each bulb burns as brightly
as when there were fewer bulbs.
FUSES
and
CIRCUIT BREAKERS
• Protect circuits from overheating because of …
– Overloaded circuit
• Overheats because resistance is lowered as objects are added
to the circuit
– Short circuit
• Overheats because there is no resistance
How FUSES and CIRCUIT
BREAKERS work
•Fuses and breakers are connected in series
• This wires in fuses
melt when overheated
• Circuit breakers open
the circuit when
overheated
MULTIMETER
• DC VOLTS - up to 1000 volts may
be measured
• AC VOLTS – up to 750 volts can be
measured.
• DC 200 and 2000 u is a very small
value for amps.
• DC 20 and 200 mA (miliamps) is a
small value for amperes.
• DC 10A (amperes) is the largest
value for amps this meter can read.
• The red test lead plugs into the
V/mA jack for testing voltage and
for small (milli-amp) currents
• The red test lead also is moved to
the 10A for larger (10 ampere)
currents.
• The black test lead always plugs
into the black COM (common) jack.
Using the Multimeter
Measuring amperage –
break the circuit and
place the meter in
series with the circuit.
Always start testing an
unknown on the 10A
setting unless told to do
otherwise!
Measuring voltage – set
the selector to DC for
battery circuits. A V or
mV will appear on
screen. A “–” on the left
side means your
polarity is negative.
Switch lead positions
for positive readings.
Study for the Test:
• Vocabulary
• Factors that change resistance…high or low
• Characteristics/examples of series and
parallel circuits
• Characteristics/examples of conductors and
insulators
• Schematic drawings…know the symbols so
you can draw a diagram