Static Electricity and Electrical Circuits

• A charge that remains stationary until it discharges onto another object.

Static Electricity

• Forces either push objects apart or pull them together.
• Electrons move as a result of electromagnetic force.
• Electromagnetic force attracts oppositely charged particles and repels particles with the same electric charge.
• When two different non-metal insulators rub together, friction can cause them to become charged.
• Electrons transfer from the surface of one material to the surface of the other.
• Charged objects attract neutral objects by inducing a charge in them.

Electrical Circuit

• A complete circular path allows electricity to flow.
• An unbroken path is necessary; a broken circuit prevents current flow.
• Includes a power supply, load, conducting path, and switch.

Power Supply

• Provides electrical energy such as a battery or power pack.

Load

• A component that transforms electricity from the power supply into useful energy like a light globe.

Conductor

• Allows electrical charge (electrons) to flow easily throughout the circuit such as copper, magnesium, and tin.

Insulator

• Does not allow the flow of electrons (electricity) but does not produce static electricity (e.g. rubber).

Current

• Measures the amount of charge (electrons/electricity) flowing around a circuit every second.
• A larger current indicates more charge (greater number of electrons) is flowing.
• Measured in ampere/amps (A) or milliamps (mA) using an ammeter in series with the circuit.
• 1 Ampere equals 1000 Milliamps.

Voltage

• Measures the energy available to push electrons around the circuit.
• Supplied by power supplies like batteries, power packs, or wall sockets.

Battery

• Features portable and light energy sources.
• Cells are single units; a battery is a collection of cells connected together.
• Batteries consist of 2+ cells connected in series to supply more voltage.
• An electric cell contains two electrodes of different materials (e.g., copper and iron).
• A substance (fluid) between the electrodes, known as the electrolyte.
• When electrodes are joined by the electrolyte, a chemical reaction occurs, releasing electrical charge (voltage).
• Dry cells contain two electrodes: a central rod of carbon (+ terminal) and a zinc case (- terminal).
• Citrus fruits' chemical reaction with acids produces a small electric current.

Series Circuits

• All components are connected one after the other, forming a circle.
• If one part fails, the entire circuit is broken, and no current flows.
• The current is the same at all points in the circuit.
• Adding more globes increases resistance, reducing current flow.
• The voltage of the supply must be split between the globes, so more components/loads reduce voltage.
• Globes cannot be controlled individually.

Parallel Circuits

• Each component is connected in a separate conducting path.
• Adding more loops lowers resistance, allowing more current to leave the power supply.
• The current splits at each branch and recombines when wires reconnect.
• If one part of the circuit fails, other parts continue to work.
• Allows more current from the power supply, lowering resistance.
• Components work at full power, using power more quickly than in series.
• Adding more globes does not affect brightness.
• Each branch can have its own switch, allowing each globe to be turned on and off.

Resistance

• Electrical resistance is how difficult it is for electrons to flow through part of a circuit.
• Resistance limits electric current flow.
• Conductors have low resistance, while insulators have high resistance.
• A material's opposition to electron flow slows down and decreases current.
• Can be added by components like light bulbs, speakers, and motors.
• It can be controlled by using variable resistors (e.g., changing radio volume or dimming light).
• Total resistance equals the sum of resistances from all components.
• Current, voltage, and resistance are related by Ohm's Law (V = I x R).
• Measured in Ohms.
• Represented by R in the formula V = I x R.

Ohm's Law

• The electric current in metallic conductors is proportional to the applied voltage and inversely proportional to the resistance.
• Materials that obey this law are considered ohmic (e.g., metals and carbon).
• A linear graph of voltage vs. electric current indicates an ohmic material.