uyer3

Forces

• A force is a push or a pull on an object
• Force is measured in newtons (N)
• Forces can change an object's shape (deformation)
• Forces can start, stop, speed up, slow down, or change the direction of an object's motion
• Acceleration is the rate at which an object's velocity changes over time due to a force
• Velocity refers to the speed and direction of a moving object
• Newton’s Third Law of Motion explains that for every action force, there is an equal and opposite reaction force
• The combined effect of multiple forces acting on an object is called the net force

Balanced vs Unbalanced Forces

• Balanced forces are equal in size and opposite in direction, resulting in a net force of zero and no motion
• Unbalanced forces are not equal, resulting in a net force greater than zero and causing motion
• Forces are represented by arrows, where the direction indicates the force's direction and the length indicates its magnitude
• Forces are measured using a spring balance, which stretches proportionally to the applied force based on Hooke's Law
• Hooke’s Law states the distance a spring moves is directly proportional to the size of the force applied

Types of Forces

• Contact forces require objects to be in contact to exert a force
• Non-contact forces (field forces) exert forces without direct contact
• Examples of contact forces: frictional, tension, normal, and applied forces
• Examples of non-contact forces include gravitational, magnetic, and electrostatic forces
• Magnets exerting force on each other without touching is an example of a non-contact force

Contact Forces

• Contact forces occur when objects are physically touching each other
• Friction is the force that opposes motion between two surfaces in contact, acting in the opposite direction of movement
• The amount of force required to move objects depends on forces like friction and the normal force
• The normal force acts perpendicular to the surface, preventing an object from penetrating it

Normal Force

• On a flat surface, the normal force equals the object's weight, but acts in the opposite direction
• Friction depends on the type of surface and the normal force
• To move an object, the applied force must be greater than the frictional force

Advantages of Friction

• Allows movement without slipping
• Provides vehicle safety by preventing skidding
• Tension occurs when an object is being pulled by forces from opposite ends
• Compression occurs when an object is being squashed by forces acting towards each other
• Bridges experience both compression and tension due to the weight of vehicles passing over them

Field (Non-Contact) Forces

• Field forces act over a distance without direct physical contact
• Common examples include gravitational, magnetic, and electrostatic forces

Gravitational Forces

• Gravitational force is the force of attraction between any two objects with mass
• It always pulls objects together
• Affected by the mass of the objects and the distance between them
• Weight (W) of an object is calculated using W = m × g, where m is mass and g is gravitational acceleration (9.8 m/s² on Earth)

Magnetic Forces

• Magnetic forces are forces of attraction or repulsion between objects due to their magnetic fields
• Only certain materials like iron, nickel, and cobalt are magnetic
• Like poles repel, and opposite poles attract
• Magnetic fields can be visualized using iron filings or field lines

Electrostatic Forces

• Electrostatic forces occur between charged objects
• Objects can be positively or negatively charged
• Friction can transfer electrons between objects
• Like charges repel, and opposite charges attract

Similarities of Field Forces

• Act over a distance without physical contact
• Can be represented by fields and field lines

Differences of Field Forces

• Gravitational force is always attractive and depends on mass and distance
• Magnetic force can be attractive or repulsive, depending on the poles
• Electrostatic force can be attractive or repulsive, depending on the charges

Field Visualisation

• Gravitational Field visualized by arrows pointing towards the center of the attracting mass
• Magnetic Field visualized using iron filings or drawn with field lines from the north to the south pole
• Electrostatic Field demonstrated by charged objects and represented by lines from positive to negative charges

Applications of Field Forces

• Gravitational Force keeps planets in orbit, causes objects to fall
• Magnetic Force used in compasses, electric motors, and MRI machines
• Electrostatic Force causes lightning, used in photocopiers

Electric Cells

• Electric cells convert chemical energy into electrical energy
• Batteries are a group of two or more electric cells connected together
• Electrode: A conductor through which electricity enters or leaves a medium
• Electrolyte: A substance that produces an electrically conducting solution when dissolved
• Half cell: One part of a twopart electrochemical cell
• Salt bridge: A device used to connect the oxidation and reduction halfcells of a voltaic cell
• Electric cells generate electricity through chemical reactions, without moving parts

Simple Lemon Battery

• Copper and zinc nails act as electrodes
• Lemon juice acts as the electrolyte
• Acidic juice in the lemon facilitates electron flow, generating electric current

Zinc-Copper Cell

• Contains two half-cells: zinc/zinc sulfate and copper/copper sulfate
• The salt bridge allows ion flow between the two solutions
• Reactions at the zinc electrode (anode): Zn → Zn2+ + 2e- (Zinc loses electrons)
• Reactions at the copper electrode (cathode): Cu2+ + 2e- → Cu (Copper ions gain electrons)
• Electron flow through the external circuit produces electric current

Understanding Electric Resistance

• Resistance is a measure of how much a material opposes the flow of electric current
• A resistor is an electrical component that adds resistance to a circuit
• Conductor: A material that allows the flow of electric charge
• Electric current is the rate of flow of electric charge in a circuit
• Electric charge is a property of matter that causes it to experience a force in an electric field
• Delocalised Electrons are not associated with a particular atom and can move freely

Electric Current

• When an energy source is connected to a conductor, it causes electrons to move, creating an electric current
• Resistance is measured in ohms (Ω)
• Ohm's Law: V = IR (Voltage = Current x Resistance)
• An electrical conductor allows electric charge to flow easily, though all have some resistance
• Resistors are specifically designed to add resistance to a circuit

Microscopic View of Resistance

• Resistance occurs when electrons collide with the atoms of the material
• Collisions transfer kinetic energy, causing the material to heat up

Uses of Resistors

• Resistors control current in electrical circuits
• Increasing resistance decreases current
• According to Ohm's Law (V = IR), increasing resistance results in a decrease in current, when voltage is fixed

Energy Transfers

• Resistors convert electrical energy into other forms like light or heat
• Some energy is always wasted

Rheostats

• Rheostats are variable resistors used to adjust current
• Used in sound equipment, dimmer switches, and motor speed controls
• Adjusting a rheostat changes the brightness of a light bulb
• Increasing resistance makes the light dimmer, while decreasing resistance makes it brighter

Light Emitting Diodes (LEDs)

• LEDs emit light when current passes through them
• Only allow current to flow in one direction & are sensitive to high currents
• Resistors are used to control current flow through LEDs
• A diode has low resistance to current in one direction and high resistance in the other
• Current can only flow in one direction through a diode

LED Efficiency

• LEDs are more efficient than incandescent bulbs
• Efficiency means producing more light (useful energy) with less electrical input energy and wasting less energy as heat

Sankey Diagrams

• Illustrate energy transfer efficiency
• Incandescent Bulb: Input Energy 100%, Useful Output (Light) 10%, Wasted Energy (Heat) 90%
• LED: Input Energy 100%, Useful Output (Light) 80%, Wasted Energy (Heat) 20%

Factors Affecting Resistance

• Type of Material
• Length of Conductor
• Thickness of Conductor
• Temperature of Conductor

Resistance and Material Type

• Different materials have different inherent resistances
• Copper has a lower resistance than iron
• A material's ability to conduct electricity is determined by its resistivity
• Low resistivity indicates a good conductor, while high resistivity means a good insulator

Thickness & Resistance

• Thickness (cross-sectional area) affects resistance
• Thicker wires have lower resistance
• Thinner wires have higher resistance
• Formula: R = (ρL)/A [ R = \frac{\rho L}{A} ]
• Where a larger A (thicker wire) results in a lower R

Length & Resistance

• The length of the conductor affects resistance
• Longer conductors have higher resistance
• Shorter conductors have lower resistance
• Formula: R = (ρL)/A [ R = \frac{\rho L}{A} ]
• Where a longer L increases R

Temperature & Resistance

• Temperature affects resistance
• Higher temperature increases resistance
• Lower temperature lowers resistance

Practical Example

• Incandescent Light Bulb: The filament is made of a long, thin tungsten wire coiled tightly
• Resistance causes the filament to heat up and emit light, and as it heats, its resistance increases

Summary of Factors

• Type of Material: Conductors like copper have low resistance, insulators like rubber have high resistance
• Thickness (Cross-sectional Area): Thicker conductors have lower resistance
• Length: Longer conductors have higher resistance
• Temperature: Higher temperatures increase the resistance of conductors

Series Circuits

• Provide only one path for electric current

Investigating Effects on Current and Potential Difference

• Potential difference (voltage) is the difference in potential energy per charge between two points in an electric circuit
• It indicates energy lost or gained by electrons passing through a resistor/cell
• Potential difference is measured using a voltmeter connected in parallel
• Ammeter measures current flow, and must be connected in series
• Ammeters have very small resistance for accurate measurement

Series Cells and Resistors

• When cells are connected in series, the total voltage is the sum of individual voltages
• Adding cells in series increases the potential difference
• Adding resistors in series increases total resistance and decreases the total current

Series Circuit

• The current is the same through each component
• The total potential difference is the sum of the potential differences across each component

Parallel Circuits

• A parallel circuit provides more than one path for electric current
• Each component is separately connected to the power source
• In circuit diagrams, components are connected with separate paths to the power source

Parallel Cell Connection

• When cells are connected in parallel, the overall potential difference remains the same as a single cell
• Advantage: increased Battery Life
• Stable Voltage
• Advantage: The voltage remains constant even if one cell is depleted

Resistors in Parallel

• Resistors in parallel provides more pathways and alternative pathways for the current
• Adding resistors in parallel decreases the total resistance
• Current divides when it enters separate branches
• Total current is the sum of currents in each branch

Potential Differences

• The potential difference across each branch is the same as the battery's potential difference

Safety Practices

• Parallel circuits are used in homes so devices operate independently, and adding devices does not increase overall resistance
• Overloading parallel circuits is risky and can lead to electrical fires.

Earthing

• Earthing connects exposed metal parts of appliances to the ground to prevent electric shocks
• Live Wire is usually Brown
• Neutral Wire is usually Blue
• Earth Wire is usually Green/Yellow
• The earth wire creates a short circuit, protecting users

Short Circuits

• A short circuit is an unintended low-resistance path that causes a surge in current
• Short circuits are a safety device that Fuses and Circuit Breakers

Fuses and Circuit Breakers

• Fuses melt and break the circuit when current exceeds a safe level
• Circuit breakers automatically break the circuit and can be reset

Earth Leakage Circuit Breakers

• Detect current leakage to the earth wire and shut off power to prevent shocks
• Typically found on the main electrical distribution board

Lightning Protection

• Lightning rods channel lightning strikes to the ground, preventing fire and damage

Illegal Electricity Connections

• Consist of connecting directly to the national grid without authorization or a meter
• Motivations include financial gain, lack of access, and avoiding payment
• Such connections bypass fee's from electricity providers like Eskom

Risks and Consequences of Illegal Connections

• Fire Risk, Electrocution, Service Disruptions, Legal Consequences, and Economic Impact

Analyzing the Dangers of Illegal Connections

• Observe Exposed Wires, Insecure Attachments, Lack of Proper Insulation
• Discuss the Fire Hazard, Electrocution Risk, and Service Disruption

Solutions

• Legal Access Programs, Education on the situation, and Enforcement

Electricity Generation

• Converts different forms of energy into electrical energy, primarily in power stations
• In South Africa, coal is predominantly used, with alternative sources also utilized

Key Terms

• Turbine: a machine for producing continuous power that is converted from various energy sources
• Generator: a device that converts mechanical energy into electrical energy
• Alternative Energy: Sources of energy that are not derived from fossil fuels
• Power Station: a facility for the generation of electrical power

Steps in Coal-Powered Power Station

• Pulverization: Coal is crushed into a fine powder
• Combustion: Pulverized coal is burnt in a furnace
• Steam Generation: Heat boils water to generate steam
• Turbine Operation: Steam pushes turbine blades, causing it to spin
• Electricity Generation: Turbine turns a generator, producing electricity
• Transmission: Electricity is sent through power lines

Disadvantages of Coal Usage

• Coal is a non-renewable energy source, contributing to environmental pollution, greenhouse gas emissions, climate change, habitat destruction, and health issues

Alternative Energy Sources

• Hydroelectric Power uses the potential energy of stored water
• Wind Power turns turbine blades
• Solar Power photovoltaic cells convert sunlight directly into electricity
• Geothermal Energy uses heat from the Earth's interior
• Biomass Energy converts organic material into electricity

Portable Generators

• Used during power outages, typically run on fuel
• Include handcrank generators, dynamos on bicycles, and larger portable units

Advantages of Alternative Energy

• Renewability, Sustainability, and Diversity

Nuclear Energy

• Nuclear power generates electricity using nuclear fission
• South Africa has one commercial nuclear power station, the Koeberg Power Station in Cape Town
• A Nuclear Power: Energy produced from controlled nuclear reactions
• Nuclear Fission: The process of splitting a heavy atomic nucleus into two smaller nuclei, releasing energy
• Nuclear Fusion: The process of combining two light atomic nuclei to form a heavier nucleus, releasing energy
• Radioactive: Emitting radiation as a result of the decay of atomic nuclei

Nuclear Process

• Some elements have unstable nuclei that spontaneously emit particles, known as radiation
• Nuclear power utilizes materials like radium and uranium that release substantial energy upon decaying
• Nuclear power stations harness the energy from nuclear fission to produce electricity
• Uranium undergoes controlled fission reactions in a reactor, producing heat that converts water to steam

Koeberg Nuclear Power Station Labeling

• nuclear reactor
• control rods
• steam generator
• turbine
• generator
• cooling system

Measures Taken for Safety

• Cooling System ensures the reactor and other components remain at safe operating temperatures
• Continuous monitoring and safety protocols protect workers and the environment from radiation exposure

Nuclear Energy Advantages

• High Energy Density, Low Greenhouse Gas Emissions, Reliability

Nuclear Energy Disadvantages

• Radioactive Waste, Safety Risks, and High Initial Costs

Disaster

• In March 2011, an earthquake and tsunami damaged the FukushimaDaiichi nuclear power plant in Japan, leading to a partial meltdown and release of radiation

National Electricity Grid

• A national electricity grid ensures electricity delivery from power stations to consumers
• Transformer: A device that changes the voltage of an electric current
• Transmission Lines: Highvoltage power lines that transport electricity over long distances
• Pylon: A tall structure that supports overhead power lines
• Power Surge: A sudden increase in voltage within an electrical circuit

Grid Overview

• The national electricity grid begins at the power stations
• Electricity is generated at high voltages to minimize energy loss during transmission
• High voltage is essential to reduce energy loss

Voltage Regulation

• Voltage levels are managed by step up and step down transformers
• StepUp Transformers increase voltage at the power station
• StepDown Transformers decrease voltage near residential and commercial areas for safe distribution

Flow of Electricity

• Coal is burned
• Water is heated to create steam
• Steam turns a turbine
• Turbine powers a generator
• A stepup transformer increases voltage
• High voltage electricity is transmitted
• Stepdown transformers reduce voltage
• Electricity is distributed

Protection from Surges and Overloads

• A power surge is a sudden spike in voltage from weather events, wiring faults, appliance usage
• Surge Protectors protect appliances
• Grid Monitoring cuts off power during a surge
• The Role of Transformers that manage voltage levels throughout the grid

What is Electrical Power?

• The rate at which electrical energy is supplied or consumed (watts)
• Watt (W): A unit of power equal to one joule of energy per second
• Rate: The speed or frequency of a particular action

Understanding Energy Consumption

• To calculate the energy consumption of an appliance, use the formula: energy = power x time
• Where the Energy is measured in joules (J)
• The power is measured in watts (W)
• The time is measured in seconds (s)
• Energy consumption is often measured in kilowatthours (kWh)

Understanding kWh

• 1 kWh is the energy used by a 1000 W (1 kW) appliance running for 1 hour
• Energy (kWh) = Power (in kW) * Time (in hours)

Calculating Electricity Costs

• Consumers are charged based on a Tiered Tariff System
• Consumers use different amounts of energy, LED's being more efficient
• Household energy usage can be acquired by conducting a survey

Electrical Power

• Definition of Electrical Power: Electrical power is the rate at which electrical energy is supplied to or consumed by an electrical device. It represents how fast the electrical energy is being used
• Watts measure the amount of Joules used in a second
• 1 watt is equivalent to 1 joule per second (1 W = 1 J/s).
• 1 Kw = 1000 Watts
• The appliance labels describe the power rating (watts) and this can be used to predict the power consumption and calculate cost