Electrical Current

Detecting electrical charge• Electroscope: an instrument to detect electrical

charge

Electrical Current• Electrical current: the movement of electric

charges in a single direction• Measured in amperes• One ampere = 6250 million electrons moving past a

single point every second

Voltage difference• Voltage difference: electrical charge flows from a

higher voltage to a lower voltage which keeps the electrical flow going• Measured in volts

Electrical Circuit • Electrical circuit: a closed path that electric current

flows through• Batteries: keep the voltage difference maintained

in the circuit in order to keep the current flowing

Dry-Cell Batteries• Dry-cell batteries: 2 electrodes surrounded by an

electrolyte• Electrode: an electric semi-conductor with a carbon

rod that is positive and a zinc part that is negative • Electrolyte: a moist paste containing several

chemicals • Use more batteries to create a higher voltage• Examples: cell phone battery, Duracell batteries,

iPod batteries

Dry-cell Batteries

Wet-cell batteries• Wet-cell batteries: contains 2 connected metal

plates in a conducting solution. The solution transfers electrons which transfers electric charge• Examples: car, truck, boat batteries

Lead-acid Batteries• Lead-acid batteries: wet-cell batteries made up of

lead plates and sulfuric acid solution• Examples: car batteries

Resistance • Resistance: the tendency for a material to oppose

the flow of electrons which changes electrical energy into thermal energy or light energy • Insulators = more resistance • Conductors = less resistance• Measured in ohms (Ω)• Copper: used in household wiring because it

produces less heat

Resistance • Factors that increase resistance of a wire:• Temperature: as the temperature of the wire

increases, the resistance increases• Length: as the length of the wire increases, the

resistance increases• Diameter: as the diameter of the wire increases,

the resistance increases

Ohm’s Law• Ohm’s Law: the current in a circuit equals the

voltage difference divided by the resistance• I = current• R = resistance• V = volts• I = V/R• R = V/I• V = IR

Electrical energy and circuits• Circuits include:1. A source of voltage difference (battery or outlet)2. A device that uses electrical energy (light bulb)3. Conductors that connect the device to the voltage

difference (wires)

Circuits in Series• Circuits in a Series: the current only has one circuit

loop to flow through

Open Circuits• Open circuit: the parts in the series are wired one

after the other, if one part is disconnected, no current flows through the circuit• Example: Christmas lights

Parallel Circuit• Parallel circuit: contains 2 or more branches for

current to flow though• The current can flow through both or one of the

branches at a time• Example: household circuits

Fuses and circuit breakers • Fuses: If the current becomes too

high, a small piece of metal melts and causes a break in the circuit, stopping the flow of current• Circuit breaker: a device that

prevents a circuit from overheating and causing a fire

Electrical Power• Electrical Power: the rate at which electrical energy

is converted to another form of energy• Equation: P = I x V• I = P/V• V = P/I• Measured in Kilowatts because watts are small

units of power

Electrical Energy • Electrical Energy: the power company charges for

the electrical energy used in your home and is measured in kilowatt hours (kWh)• Electrical energy equation: E = P x t• P = E/t• t = E/P