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ELECTRICITYChapter 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
• This wires in fuses melt when overheated
• Circuit breakers open the circuit when overheated
•Fuses and breakers are connected in series
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