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