Unit 3 - Electrical Energy
Electrical energy: the energy of charged particles
electrical energy has many applications
What uses electrical energy?
the human body - like moving your eyes to read relies on electrical signals in your muscles. Electrical signals help maintain breathing and heart beat
Technology - like touch-sensitive screens and robots
Many different types of energy can be transformed into electrical energy
energy is neither created or destroyed
It is transformed from one kind of energy to another kind of energy
Types of energy
1) mechanical energy: the sum of kinetic energy and potential energy
2) kinetic energy: energy of movement
3) potential energy: stored energy that a system has due to its position or condition (water at the top of a waterfall before it falls because it has potential energy)
4) chemical energy: energy stored in chemical bonds and released when a chemical reaction occurs (batteries store chemical energy, chemical energy is stored in animal and plants is called biomass, fossil fuels like coal/oil/natural gas store chemical energy)
5) solar energy: energy carried by electromagnetic radiation given off by the sun
fossil fuels and biomass result form energy from the Sun being captured by plants and plant-like organisms
6) Nuclear energy: energy generated by forming new atoms
Nuclear fusion: new atoms are made as smaller atoms collide and fuse (sun and stars) → forms Hydrogen bombs
Nuclear fission: new atoms are made by splitting larger atoms (carried out in reactor on earth). Most of the energy is thermal energy, which is used to boil water into steam. Pressure from the moving steam turns turbines connected to generators
7) thermal energy: energy due to the rapid motion of particles that make up an object, detected as heat
sources include nuclear reactions or from earth’s interior (geothermal energy), where steam and hot water from naturally
→ like geysers, volcanoes, hot springs
Electrical energy is generated in different ways from different sources.
most of the electrical energy in Canada is generated by transforming kinetic energy into kinetic energy
Source of kinetic energy may be moving water, wind, or moving steam produced by nuclear reactions or burning fossil fuels
Kinetic energy to electrical energy: generator system
Generator system: a system that transforms kinetic energy to electrical energy
Turbine: steam, water, or wind causes the turbine to spin
Shaft: as the turbine spins, the shaft spins
Generator: kinetic energy of the spinning shaft is transformed into electrical energy inside the generator
Most of the electrical energy in Canada comes from river flow, fossil fuels, and nuclear reactions
BC uses river flow and fossil fuels
river flow is the main source (hydroelectric energy)
Water flowing freely in a river turns a turbine
thermal energy from burning cal is used to boil water into steam
Other energy sources include:
Wind: kinetic energy of wind is transformed into electrical energy as the moving air turns the sunlight
Sunlight: photovoltaic cels transform the energy of visible light to electrical energy
when visible light strikes electrons in the photovoltaic cells, the electrons absorb enough energy to flow freely and generate electrical energy
Geothermal sources: When earth’s crust is thin and molten rock comes close to the surface, hot steam can be used to to turn turbines to generate electrical energy
Waves and tides: tides and the rise and fall of waves can turn turbines to generate electrical energy
STATIC CHARGE
Static charge: electric charge that stays in one place until it is discharged to other objects or to the air
measured in coulombs : unit of electric Charge
It takes the addition or removal of 6.25 × 10^18 electron to produce 1C of charge
Positive and Negative charge in the atom
atoms contain protons and neutrons in their nucleus and electrons outside the nucleus
If the number of positive charges equal the number of negative charges, the object is neutral
uncharged materials:
before two materials are rubbed together: they have equal numbers of positively charged proton and negatively charged electrons = neutral
If number of positive charges equal the number of negative charges, the object is neutral
In a solid material the positive nucleus sty in the centre of the atom, but the electron can be rubbed off a material
All solid materials are charged by the transfer of electrons
charged materials:
If electrons rubbed off one material, the protons stay behind and the material becomes electrically charged
the material that gains the electrons also becomes electrically charged
Electrically charged materials have an unequal number of positive and negative charges
When a neutral atoms loses electrons (now more protons) it becomes positive
When a neutral atom gain electrons (now more electrons) it becomes negative
Friction and electron transfer
Friction: occurs when objects rub against each other
results in one object losing electrons while the other object gains electrons
Electrons with either stay on the surface of the new material or travel through it
Insulators and Conductors
Insulators: materials that do NOT allow electrons to move easily
can retain a static charge
Eg. glass, plastics, ceramics, and dry wood
Conductors: materials that allow electrons to move easily
will allow a charge to flow
Eg. metals
Hair tends to lose electrons while rubber tends to gain electrons
Conductivity:
an indication of how easily charges travel through a material
Electrons can move through almost all metals (conductors); can move through some metals more easily than others
The higher the conductivity of a material, the more easily electrons can move through
Generating Static Charge
Van de Graff generator: uses friction to produce a large static charge on a metal dome
a moving belt produces a static charge at the base of the generator
The belt carries the charge to the metal dome, where it collected
Grounding-connecting a conductor so that electric charge flows into the earths surface
Lightning: static electricity on a much larger scale
rubbing caused by air moving around
Thunderclouds bottom is usually negative, top is positive
Electric Force
A force is a push or a pull
contact forces: forces that can have an effect only on objects when they touch
Action-at-a-distance: forces that can have an effect only an object without touching it
Electric force: push or pull between charged objects
An electric force is an example of an action-at-a-distance force
Laws of static charge
Like charges repel
Opposite charges attract - ionic compound formation
Neutral objects are attracted to charged objects
positive - neutral attract
Negative - neutral attract
Coulomb’s Law
if the amount of charge increases, the electric force increases
If the distance between charged objects increases, the electric force decreases
Charging by conduction
charging by conduction: objects become charged through contact
when objects touch, electrons move from one object to the other
Eg. Walking across a carpet and touching a metal doorknob
charging by induction
when objects are charged without touching or making any direct contact
Electrons do not move from one object to another
Electrons reposition themselves in the object that becomes charged
Because no electrons are transferred, the charge is only temporary
Eg. Dust on the Tv screen
Attraction of Neutral Objects
induction explains why neutral objects are attracted to charged objects
Neutral objects are attracted to harged objects because the neutral objects are temporarily charged by induction
Ex. A balloon that is rubbed on a sweater (charged by conduction) and becomes negatively charged will stick to a neutral wall
the balloons negative charges repel the wall’s negative charges
The wall temporarily becomes positively charged by induction
Electric Potential Energy and Voltage
Electrochemical cells: converts chemical energy into electrical energy
Battery: a single electrochemical cell or a combination of electrochemical cells connected together
Terminals: end points of an electrochemical cell/battery where connections are made
Negative terminal: end where electrons accumulate
Positive terminal: end that has lost electrons
Producing Voltage
the two terminals in an electrochemical cell/battery are called electrodes
The electrodes are in an electrolyte which is a substance that conducts electricity
There are two groups of cell:
Dry cells: electrolyte is a moist paste that surrounds electrode. (Used in flashlights and watches)
Wet cells: electrolyte is a liquid that is used in cars and motorcycles
The amount of voltage that is produced in an electrochemical cell depends on the types of metal (electrodes) and electrolyte used
most electrochemical cells produce 1.5 or 2V
Electric Potential Energy
electric energy is the ability to do work
Electric energy can do work
When unlike charges are moved farther apart, they gain electric potential energy
Electric energy that is stored is potential energy
Electric potential energy: the electrical energy stored in an electrochemical cell
Electric energy that is moving is kinetic energy
Electric potential difference
Voltage: the amount of electric potential energy per coulomb of charge
Volt (V): the unit of measure for voltage
Voltmeter: measures voltage between two location of charge separation
The actual electric potential energy is the product of both the voltage and the amount of charge
ENERGY = VOLTAGE X CHARGE
Joules / coulombs = volts
Electric current
Electric circuit: a complete pathway that allows electrons to flow
Energy around a circuit:
Chemical energy in the battery separates positive and negative charges and gives electrons on the negative terminal electric potential energy
Electrons move across the wire as they are repelled by the negative terminal and attracted to the positive terminal
Potential energy is transformed into other forms of energy when it passes through a load (in buzzers, it is transformed into sound energy
Circuit Components
source: where the electrical energy comes from (electrochemical cell or battery)
Conductors: the wire through which electric current flows
Load: a device that converts electrical energy into other forms of energy
Eg. Light bulbs, heaters, radios
As electrons pass through a load, they lose energy as electrical energy is converted to another type of energy
A load resists (hinders) the flow of current
Electrons in the current collide with atoms that make up the load or with each other
Collisions interfere with teh flow of current
Electrons in the current collide with atoms that make up the load or with each other
Collisions interfere with the flow of current
Switch: a device that can turn the circuit on or off by closing or opening the circuit
Controls the flow of current
Circuit diagram: uses symbols to represent different components of an electric circuit
long line in cells/batteries are positive terminals and short = negative
Electrons are so pushy!
all electrons have a negative charge
This means electrons repel and push each other
Electrons in every part of a circuit are pushing each other so when a circuit is closed they load works immediately
Current electricity
when a battery is connected to a complete circuit it causes electrons to move
Moving electrical charges form an electric current
Current electricity: the continuous flow of charge in a complete circuit
Chemical energy from a source (cell or battery) causes charges to move through a conductor (wires), carrying energy to an electrical device (cellphone)
The moving charges are called an electric current
Current: the measure of flow
Electric current: the amount of charge passing a point ina conductor every second
CURRENT = I
measured in amperes (A)
One coulomb of charge passing a given point per second
Ammeter: a device used to measure the current in a circuit
Modelling the flow of current:
Negative terminal repels the negative charges already in the conductor
positive terminal attracts the negative charges already in the conductor
electrons move along the conducting wires; electrons from the electrochemical cell move into the conductor
As electrons pass through the load, they transfer some of their energy to the load
the electrons then leave the load and return to the electrochemical cell
Electrons enter the electrochemical cell; combine with positive ions to become neutral
overtime: fewer electrons at negative terminal; fewer positive ions at positive terminal
The worker (chemical energy) can carry more electrons up the ladder, keeping the number of separated charges equal