Science 9 - Electrical Energy and Circuits

Fundamentals of Electrical Energy

• Definition of Electrical Energy: It is the energy of charged particles.

• Applications in the Human Body:     * Using eyes to read relies on electrical signals in the muscles.     * Electrical signals help maintain breathing and the heartbeat.

• Applications in Technology: Examples include touch-sensitive screens and robots.

Types of Energy and Transformations

• Law of Conservation of Energy: Energy is neither created nor destroyed; it is transformed from one kind of energy to another.

• Mechanical Energy: The sum of kinetic energy and potential energy.

• Kinetic Energy: The energy of motion.

• Potential Energy: Stored energy that a system has due to its position or condition.     * Example: Water at the top of a waterfall, just before it falls, possesses potential energy because of its position and kinetic energy because it is moving.

• Chemical Energy: Energy stored in chemical bonds and released when a chemical reaction occurs.     * Batteries: Store chemical energy.     * Biomass: Chemical energy stored in animals and plants.     * Fossil Fuels: Coal, oil, and natural gas store chemical energy.

• Solar Energy: Energy carried by electromagnetic radiation given off by the Sun.     * Fossil fuels and biomass result from energy from the Sun being captured by plants and plant-like organisms.

• Nuclear Energy: Energy generated by forming new atoms.     * Nuclear Fusion: New atoms are made as smaller atoms collide and fuse (occurs in the Sun and stars).     * Nuclear Fission: New atoms are made by splitting larger atoms (carried out in reactors on Earth). In this process, most of the energy is thermal energy, which is used to boil water into steam. The pressure from moving steam turns turbines connected to generators.

• Thermal Energy: Energy due to the rapid motion of particles that make up an object, detected as heat.     * Sources: Nuclear reactions or Earth's interior (geothermal energy) where steam and hot water form naturally.     * Examples: Geysers, volcanoes, and hot springs.

Generation of Electrical Energy

• General Transformation: Most electrical energy in Canada is generated by transforming kinetic energy into electrical energy.

• Sources of Kinetic Energy: Moving water, wind, or moving steam produced by nuclear reactions or burning fossil fuels.

• The Generator System: A system that transforms kinetic energy into electrical energy consisting of:     * Turbine: Steam, water, or wind cause 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.

• Energy Sources in British Columbia: Primarily uses river flow and fossil fuels.     * River Flow: The main source (hydroelectric energy) where water flowing freely in a river turns a turbine.     * Fossil Fuels: Thermal energy from burning coal is used to boil water into steam.

• Other Energy Sources:     * Wind: Kinetic energy of wind is transformed into electrical energy as moving air turns a turbine.     * Sunlight (Photovoltaic): Photovoltaic cells transform visible light energy directly into electrical energy. When visible light strikes the cells, electrons absorb enough energy to flow freely and generate current.     * Geothermal: Where the Earth's crust is thin and molten rock is near the surface, hot steam can be extracted to turn turbines.     * Waves and Tides: The physical rise and fall of waves and tides can be harnessed to turn turbines.

Static Charge and Atomic Structure

• Static Charge (Static Electricity): Electric charge that stays in one place until it is discharged (lost) to other objects or the air.

• Unit of Measurement: Measured in Coulombs $(C)$.     * $1.0\,C$ of charge requires the addition or removal of $6.25 \times 10^{18}$ electrons.

• Atomic Components:     * Protons: Positive charge; located in the nucleus.     * Neutrons: Neutral charge; located in the nucleus.     * Electrons: Negative charge; located outside the nucleus.

• Neutral Objects: An object is neutral if the number of positive charges equals the number of negative charges.

• Charging Solids: In solid materials, the positive nucleus stays in the center, but electrons can be rubbed off. All solid materials are charged by the transfer of electrons.

• Charged Materials:     * If electrons are rubbed off, the protons stay behind, and the material becomes electrically charged.     * The material that gains electrons also becomes electrically charged.     * Materials have an unequal number of positive and negative charges.     * Loss of electrons: Neutral atom becomes positive.     * Gain of electrons: Neutral atom becomes negative.

Friction, Conductors, and Insulators

• Friction: Occurs when objects rub against each other, resulting in one object losing electrons and the other gaining them.

• Insulators: Materials that do not allow electrons to move easily (e.g., glass, plastics, ceramics, dry wood). They can retain a static charge.

• Conductors: Materials that allow electrons to move easily (e.g., metals). They allow a charge to flow.

• Conductivity: An indication of how easily charges travel through a material. Higher conductivity means electrons move more easily.

• Van de Graaff Generator: Uses friction to produce a large static charge on a metal dome. A moving belt produces a charge at the base and carries it to the dome where it collects.

• Grounding: Connecting a conductor so that electric charge flows into the Earth's surface.

• Lightning: Static electricity on a much larger scale. Rubbing is caused by air moving in thunderclouds; the bottom is usually negative and the top is positive.

The Laws of Static Charge

• Electric Force: A push or pull between charged objects. It is an action-at-a-distance force (affects objects without touching).

• Law 1: Like charges repel (Positive/Positive or Negative/Negative).

• Law 2: Opposite charges attract (Positive/Negative).

• Law 3: Neutral objects are attracted to charged objects (Positive/Neutral or Negative/Neutral).

• Coulomb's Law Variables:     * If the amount of charge increases, the electric force increases.     * If the distance between charged objects increases, the electric force decreases.

Charging by Conduction and Induction

• Charging by Conduction: Objects become charged through physical contact. Electrons move from one object to another.     * Example: Walking across a carpet and touching a metal doorknob.

• Charging by Induction: Objects are charged without touching or direct contact. Electrons do not move from one object to another but reposition themselves within the object.     * This charge is temporary because no electrons are transferred.     * Example: Dust on a TV screen.

• Attraction of Neutral Objects: Explained by induction. A balloon rubbed on a sweater (charged by conduction) becomes negative. When brought near a wall, it repels the wall's negative charges, making the wall temporarily positive by induction, so the balloon sticks.

Electric Potential Energy and Voltage

• Electrochemical Cells: Convert chemical energy into electrical energy.

• Battery: A single electrochemical cell or a combination of cells connected together.

• Terminals: End points of a battery.     * Negative Terminal: Where electrons accumulate.     * Positive Terminal: The end that has lost electrons.

• Electrodes and Electrolytes: Electrodes are the two terminals (metals). The electrolyte is a substance that conducts electricity.     * Dry Cells: Electrolyte is a moist paste (flashlights, watches).     * Wet Cells: Electrolyte is a liquid (cars, motorcycles).

• Voltage production: Depends on the types of metal (electrodes) and the electrolyte used. Most cells produce $1.5\,V$ or $2\,V$.

• Electric Potential Energy: Electrical energy stored in an electrochemical cell. It is the ability to do work.     * When unlike charges are moved farther apart, they gain electric potential energy.     * Moving electric energy is kinetic energy.

• Electric Potential Difference (Voltage): The amount of electric potential energy per coulomb of charge. Measured in Volts $(V)$.

• Voltmeter: Measures voltage between two locations.

• Formula: $\text{Energy} = \text{Voltage} \times \text{Charge}$

Electric Circuit Components and Symbols

• Electric Circuit: A complete pathway that allows electrons to flow.

• Energy Flow:     1. Chemical energy in the battery separates charges, giving negative terminal electrons potential energy.     2. Electrons are repelled by the negative terminal and attracted to the positive terminal, moving across the wire.     3. Potential energy is transformed into other forms (e.g., sound in buzzers) in a load.

• Circuit Components:     1. Source: Origin of electrical energy (battery/cell).     2. Conductor: Wire through which current flows.     3. Load: Device that converts electrical energy into other forms (light, heat, sound). Loads resist/hinder the flow of current due to electron collisions.     4. Switch: Device that turns a circuit on (closed) or off (open).

• Standard Symbols:     * Cell: One long line ($+$), one short line ($-$).     * Battery: Multiple cells in series.     * Load: Resistor zigzag or lightbulb circle symbol.     * Voltmeter ($V$): Measures potential difference.     * Ammeter ($A$): Measures current.     * Ohmmeter ($\Omega$): Measures resistance.

• Current Electricity: The continuous flow of charge in a complete circuit.

Electric Current and Ohm's Law

• Electric Current ($I$): The amount of charge passing a point in a conductor every second. Measured in Amperes $(A)$.     * $1\,A = \text{one coulomb per second}$.

• Resistance ($R$): The property of a material that slows down electron flow and converts electrical energy into other forms. Measured in Ohms $(\Omega)$.

• Factors Affecting Resistance:     * Length: Longer materials have more resistance.     * Cross-Sectional Area: Thinner materials have more resistance.     * Material: Conductivity and resistivity vary by material.

• Ohm's Law: The ratio of voltage to current.     * $\text{Voltage }(V) = \text{Current }(I) \times \text{Resistance }(R)$     * Voltage is directly proportional to current.     * Resistance and current are inversely proportional.

• Short Circuit: A circuit with resistance so low the current becomes dangerously high, potentially causing fires.

• Safety Practices:     * Never touch exposed wires.     * Keep water away.     * Don't overload outlets.     * Fuse: Metal filament that melts to break the circuit; requires replacement.     * Circuit Breaker: Switch that shuts off power; can be reset.

• Unit Prefixes:     * milli ($m$) = $1/1000$     * kilo ($k$) = $1000$     * mega ($M$) = $1,000,000$

Ohm's Law Examples

• Example 1: A starter motor with $12\,V$ and $75\,A$ current.     * $R = \frac{12\,V}{75\,A} = 0.16\,\Omega$

• Example 2: A $92\,\Omega$ resistor with $78\,mA$ ($0.078\,A$) current.     * $V = 0.078\,A \times 92\,\Omega = 7.176\,V \approx 7.2\,V$

Series and Parallel Circuits

• Series Circuits: Only one path for current. Electrons must travel through all components.     * If one part is blocked (open switch), the current stops completely.     * Voltage: Total voltage is the sum of voltages lost at each load ($V_{\text{total}} = V_1 + V_2 + V_3$).     * Current: Equal in every part of the circuit ($I_1 = I_2 = I_3$).     * Resistance: Adding resistors in series increases total resistance and decreases total current.

• Parallel Circuits: More than one path for current.     * Voltage: Voltage lost on each separate pathway is the same ($V_1 = V_2 = V_3$).     * Current: Total current entering a junction point equals the sum of current leaving ($I_{\text{total}} = I_1 + I_2 + I_3$).     * Junction Point: Where a circuit divides into multiple paths or joins together.     * Resistance: Placing resistors in parallel creates more pathways, which decreases total resistance.

Electrical Power and Billing

• Power ($P$): The rate at which work is done or energy is transformed. Measured in Watts $(W)$.

• Electrical Power: The rate at which a load uses electrical energy.     * Phantom Load: Energy a device uses when turned off (e.g., stand-by mode).

• Power Formula:     * $\text{Power }(P) = \text{Voltage }(V) \times \text{Current }(I)$

• Calculation Examples:     * Light bulb with $0.625\,A$ and $120\,V$: $P = 120 \times 0.625 = 75\,W$.     * PS rated at $380\,W$ on $120\,V$ outlet: $I = \frac{380}{120} = 3.167\,A$.

• Energy ($E$): Calculated as $\text{Power} \times \text{Time}$.     * Kilowatt-hour ($kW \cdot h$): Large unit of energy. $1.0\,kW \cdot h = 1.0\,kW \times 1.0\,h$.

• Paying for Electricity:     * Smart Meter: Measures how energy use changes throughout the day.     * Example Bill: $12,000\,kW \cdot h$ at $7.38\,\text{cents/kWh}$.     * $\text{Cost} = 12,000 \times 0.0738 = \$885.60$

Sustainability and Ethical Perspectives

• Renewable Energy Sources: Available on a continuous basis (sunlight, wind, river flow, tides, biomass).     * BC Examples: Bennett Dam, Bear Mountain Wind Park, Klemtu Hydro and Solar Project.

• Nonrenewable Energy Sources: Limited in a human lifetime (coal, natural gas, uranium).

• Sustainable Energy System: Produces and uses energy such that it has limited impact on environmental and human health, relies less on nonrenewables, and ensures affordability for future generations.

• First Peoples Ecosystem Based Management (EBM):     * Respect and Responsibility: Making decisions that respect the natural world and responsible resource use.     * Intergenerational Knowledge: Listening to Elders and sharing knowledge between generations.     * Balance and Interconnectedness: Balancing future needs and recognizing complex ecosystem relationships.     * Giving and Receiving: Giving thanks for resources and sharing benefits within a community.