Moving electricity

Conductors A material through which electric charge can easily flow. There are different levels of conductivity Charge flows because of the availability of loosely held electrons, which move throughout the conductive material.

Insulator “A material that is a poor conductor of electricity.” In insulating materials, the outer electrons are not so free to move.

Conductors Vs. Insulators Semiconductors are materials that can be made to behave like either an insulator or a conductor. Computer circuit parts Certain metals, at very low temperatures, can be superconductors. Superconductors are excellent conductors with almost zero resistance to the flow of charge.

Conductors & Insulators Examples Air Wood Rubber Glass Plastic Conductors All metals – (some more conductive than others) Graphite Ionic Solutions

Electric circuits Electrons flow through a closed continuous path called a circuit The power to move those electrons comes from a voltage potential difference It is measured in volts (V) The voltage potential difference is provided by a voltage difference such as a dry cell, wet cell, or generator

Electrical Potential The electrical potential energy per unit of charge is the electric potential.

Dry Cell Battery

Wet Cell Car battery

Generator Turning a coil of wire in a magnetic field creates electric current.

Current Current is a measurement of the flow of electrons in a circuit It is measured in amps (A) and represented by the letter I Anything that opposes the flow of electrons in a circuit is a resistor The amount of resistance (R) is measured in ohms Ω

Electrical Resistance Resistance in a wire depends on: Conductivity of the material (how well it conducts) Thickness (width) of wire Thick wires have less resistance then thin wires Length of wire Longer wires have more resistance than shorter wires Temperature Increased temperature = increased resistance.

Resistance In many instances, resistance is when electricity (voltage and charge) is turned into another form of energy.

Ohm’s law The amount of current in a circuit is calculated by Ohm’s law I = V/R

Electron movement vs convention We know that electrons, not protons move. However, before this was understood, it was thought that electricity moved DOWN the potential (positive to negative), so we still conventionally say electricity moves from positive to negative

Types of current Current can be either alternating current (AC) or direct current (DC) In direct current the electrons flow in one direction only (from the negative to the positive) Batteries provide direct current

Alternating current Voltage sources such as wall outlets provide alternating current In alternating current, the electrons flow first in one direction, then in the opposite direction The frequency (times per second) that the electron flow changes direction is measured in Hertz In the US, the standard AC current is 60 HZ and the standard voltage is 120 V

Changing current House current is alternating, your cell phone is direct current To change AC to DC (like to charge your battery), a device called an adaptor is used It not only changes the current, it changes the voltage by using a transformer

Electric Shock The damage from electric shock is from current that passes through your body.

Electric Shock Dry skin resistance = up to ~50,000 Ω If the resistance of your body were 50,000 Ω dry, what would be the current in your body when you touched the terminals of a 12-volt battery? Wet skin resistance (salt water) = as low as ~200 Ω If your skin were very moist so that your resistance was only 200-Ohms, and you touch the terminal of a 12-volt battery, how much current would you draw?

Types of circuits Series—all resistors are in the same path If one resistor fails, all resistors will not work Total resistance in the circuit is the sum of all resistors—voltage is divided Parallel—each resistor is on its own path Overall resistance decreases each time a new branch is added—voltage stays the same

Types of Circuits Parallel Circuit Series Circuit Single pathway for electrons (charge) to flow between the terminals of the battery or wall socket Parallel Circuit Multiple branches (or separate paths) for the flow of electrons (charge).

Circuit safety If too much resistance is in a circuit, the wires or resistors can become too hot To prevent a fire or damage to the resistor, circuits have fuses or circuit breakers If the resistance becomes too high, the fuse will melt or the circuit breaker will trip, causing the circuit to open, just like flipping the switch. The circuit will not work again until the fuse is replaced or the breaker switched back

Fuses Small pieces of metal that melt when heated too hot

Circuit breaker A device in a circuit that opens a switch if resistance becomes too high

Schematic Diagrams Use symbols to represent parts of a circuit. Conductor (wire) Cell Batteries (2+ cells) Light bulb Open or closed switch Misc. Resistor

Electric power The rate at which electric energy is changed to heat, light, or mechanical energy Electric power = current x voltage P = I X V Measured in watts (W) or Kilowatts (kW)

Electric energy Electric power used for an amount of time Energy = power X time E = P x t It is measured in joules or kWh (kilowatt-hour) Your electric bill is based on this. You are charged cents per kWh