ELECTRICITY

• Electric devices, such as stereos, lights, and toasters, work when there is an electrics through them.
• Electric current is the net movement of electric charges in a single direction.
• Electric current is measured in amperes (A), named after the French scientist and mathematician Andre Marie Ampere.
• One ampere is equal to one coulomb of electric charge flowing past a point every second.
• The ball changes direction when it strikes a stair, but the net motion of the ball is downward.
• In a metal wire without an electric current, electrons are in constant motion in all directions, resulting in no net movement of electrons in one direction.
• When there is an electric current in the wire, electrons continue their random movements but also drift in the direction of the current.
• The movement of an electron in an electric current is similar to a ball bouncing down a flight of stairs.
• Alternating Current in AC/DC stands for current from household electrical outlets.
• Alternating current is used in power grids and by appliances such as toasters and hair dryers.
• Direct current never changes direction.
• An AC/DC adapter is a device that converts the alternating current of an electrical outlet into direct current.
• With an AC/DC adapter, you can charge a cell phone battery with the current from an electrical outlet.
• Electric power grids are built so that alternating current changes direction 120 times per second.
• Battery-powered devices, such as flashlight, use direct current.
• The electric force that causes charges to flow is similar to the force acting on the water in a pipe.
• Water flows from higher pressure to lower pressure, as shown in Figure 4.12.2.
• In a similar way, electric current is from higher voltage to lower voltage.
• A voltage difference is related to the force that causes electric charges to flow.
• Voltage difference is measured in volts (V), named after Alexander Volta who invented the first electric cell.
• An electric circuit is a closed path that electric current follows. If the battery, the lightbulb, or one of the wires is removed from the path in figure below, the electric circuit is broken and there will be no current.
• Resistors are striped objects found inside computers, radios, and telephones, designed to resist the flow of electrons.
• Electrical engineers use resistors to reduce the current through all or part of a circuit.
• Resistors help protect more delicate electronic components from melting or breaking if too much current is sent through them.
• When electrons move through a resistor, some energy is transferred to that resistor.
• Resistance, which is measured in ohms (Q), is the tendency for a material to resist the flow of electrons and to convert electrical energy into other forms of energy, such as thermal energy.
• Cell phones can get hot during a long telephone call due to the resistance of the circuit.
• Almost all materials have some resistance.
• Even copper wires have some resistance.
• The resistances of long copper wires can noticeably affect the currents through a circuit.
• Ohm's law states that the voltage difference, current, and resistance in a circuit are related.
• The relationship between voltage difference, current, and resistance in a circuit is known as Ohm's law.
• According to Ohm's law, the current in a circuit equals the voltage difference divided by the resistance.
• If voltage is measured in volts (V) and resistance is measured in ohms (Q), then current is measured in amperes (A).
• A series circuit is an electric circuit with only one branch
• Parallel circuits contain two or more branches for current.