Circuits

• An electric circuit is a path through which charges can be conducted.
• An electric circuit isa set of electrical components connected such that they provide one or more complete paths for the movement of charges.
• The conducting path produced when a light bulb is connected across the battery’s terminals is called a closed circuit.
• Without a complete path, there is no charge flow and therefore no current. This is called an open circuit.
• Switches interrupt the flow of charges in a circuit.
• You can use a switch to open and close a circuit.
• Schematic diagrams are used to represent circuits.
• A schematic diagram is a graphical representation of a circuit that uses lines to represent wires and different symbols to represent components.
• Each element used in a piece of electrical equipment is represented by a symbol that reflects the element’s construction or function.
• Series circuits have a single path for current.
• When appliances or other devices are connected in a series circuit, they form a single pathway for charges to flow.
• In a series circuit,the components of a circuit form a single path for current.
• The current in each device is the same.
• The resistances may be different.
• The voltage across each device in a series circuit can be different.
• If one element along the path in a series circuit is removed, the circuit will not work.
• Parallel circuits have multiple paths for current.
• A parallel circuit is a circuit in which all of the components are connected to each other side by side.
• The voltage across each device is the same.
• The current in each device does not have to be the same.
• A break in any one path in a parallel circuit does not interrupt the flow of electric charge in the other paths.

Electric Power and Electrical Energy

• Electrical energy is the energy that is associated with charged particles because of their positions.
• Electric power is the rate at which electrical energy is used in a circuit.
• The rate at which electrical work is done is called electric power.

POWER =(CURRENT )(VOLTAGE) = P= IV (p= power, I = current, v = voltage)

• The SI unit for power is the watt (W).
• 1 W = 1 A ´ 1 V
• If you combine the electric power equation above with the equation V = IR, the power lost, or dissipated, by a resistor can be calculated.

P = I 2R = V 2/R

• Electric companies measure energy consumed in kilowatt-hours.
• 1 kW•h = 3.6 ´ 10 6 J.

Fuses and Circuit Breakers

• When electrical wires carry more than a safe level of current, the circuit is said to be overloaded.
• A short circuit can happen if a wire’s insulation wears down, two wires may touch, creating an alternative pathway for current.
• Fuses melt to prevent circuit overloads.
• A fuse an electrical device that contains a metal strip that melts when current in the circuit becomes too great.
• Circuit breakers open circuits with high current.
• A circuit breaker a switch that opens a circuit automatically when the current exceeds a certain value.
• The circuit breaker acts as a switch.
• Unlike fuses, circuit breakers can be reset by turning the switch back on.