ELECTRIC CURRENT

What is current electricity? Current Electricity - Flow of electrons What causes electrons to flow? When an electric force is applied, it causes a potential difference or difference in voltage between the ends of a conductor. When there is no potential difference, the flow of charge stops.

Direct Current and Alternating Current Direct Current – flow of charge always flows in one direction. Batteries use DC to flow from the negative terminal to the positive terminal. Alternating Current – electrons move back and forth about relatively fixed positions. Power utilities use AC. AC allows low-cost, high voltage energy transmission across great distances, with safe low-voltage use by the consumer.

Potential difference or voltage difference causes electrons to flow in one net direction. This voltage difference provides the “push” or the “pressure” to move in a given direction, and the SI unit is Voltage (volts)

Voltage Sources Voltage sources: dry cell batteries, wet cell batteries, lead- acid batteries and generators. They supply the energy or the “push” to allow the charges to move.

Voltage Sources Dry Cell Batteries Consists of two electrodes surrounded by an electrolyte. Consists of two electrodes surrounded by an electrolyte. In the dry cell shown here, one electrode is the carbon rod and the other is the zinc container. In the dry cell shown here, one electrode is the carbon rod and the other is the zinc container.

Voltage Sources Wet Cell Batteries Contains two connected plates made of different metals in a conducting solution. Contains two connected plates made of different metals in a conducting solution.

Voltage Sources Lead-Acid Batteries Most car batteries are lead-acid batteries. Most car batteries are lead-acid batteries. Contains six wet cells made of lead and lead dioxide plates in a sulfuric acid solution. Contains six wet cells made of lead and lead dioxide plates in a sulfuric acid solution.

Voltage Sources In dry and wet cell batteries, a chemical reaction occurs releasing energy inside the cell which is then converted to electrical energy. Generators, like the alternators in vehicles, convert mechanical energy to electrical energy.

Resistance Resistance is the tendency of a material to oppose the flow of electrons, changing electrical energy into thermal energy and light.

Resistance Almost all materials have some electrical resistance. Conductors have less resistance than insulators.

The SI unit for resistance is

Resistance Temperature, Length, and thickness affect the amount of resistance of a material. Resistance increases as temperature increases.

Resistance Resistance increases as wire becomes longer or as the gauge (diameter) becomes thinner.

Electric current is the flow of electric charge and is measured in amperes (amps). Amperes can be though of as the volume of current running through a circuit.

Current in a Simple Circuit A simple circuit contains: 1)A voltage source 2)A resistor (such as a light bulb) 3)Conductors that connect the device to the voltage source.

Current in a Simple Circuit Voltage, current, and resistance in a simple circuit are related. This relationship is known as Ohm’s law.

Current in a Simple Circuit Ohm’s Law can be written as: V=IR V= Voltage I= Amperage R= Resistance

ELECTRICAL ENERGY

SERIES AND PARALLEL CIRCUITS What is a series circuit? A series circuit has only one path for current.

SERIES AND PARALLEL CIRCUITS What is a parallel circuit? A parallel circuit has multiple paths for current.

SERIES AND PARALLEL CIRCUITS For a circuit to allow the flow of electrons, it must be closed which means that it makes an complete loop back to the power source.

SERIES AND PARALLEL CIRCUITS If it is open, the path that electrons can follow is broken and the resistor will not work.

SERIES AND PARALLEL CIRCUITS If there is a short circuit, the resistor will not work, even though there is a complete path. The reason is because electricity will always follow the path of least resistance and will therefore not travel through the resistor.

SCHEMATIC DIAGRAMS Schematic Diagrams are used to represent circuits.

FUSES AND CIRCUIT BREAKERS How do fuses work? Fuses melt to prevent circuit overloads. A fuse is a ribbon of wire with a low melting point A fuse is a ribbon of wire with a low melting point How do circuit breakers work? Circuit breakers open circuits with high current. Made of a magnet or bimetallic strip Made of a magnet or bimetallic strip

Electrical Power Electrical Power is the rate at which electrical energy is converted into another form of energy, and can be written as: P=IR P=power I=Ampere R=Resistance