ELECTRICITY Chapter 13.2 – 13.3 VOLTAGE / AMPERAGE / WIRE / BATTERY / SERIES / PARALLEL / MULTIMETER

VOLTAGE – page 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 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