Transcript Electrical Current

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