Electricity and Energy Concepts

Circuit Devices

• LDR (Light Dependent Resistor): Resistance decreases with light intensity; used in outdoor lighting, burglar detectors.
• Thermistor: Resistance decreases with temperature; used in temperature detectors.

Series and Parallel Circuits

Series Circuits

• If one component fails, all components stop working.
• Current is constant throughout.
• Total resistance sums up.

Parallel Circuits

• If one component fails, others remain functional.
• Voltage remains constant across components.
• Total current is the sum of currents through components.
• Adding resistors decreases total resistance.

Electricity in the Home

• AC (Alternating Current): Changes direction, UK mains is 230V, frequency of 50Hz.
• DC (Direct Current): Flows in one direction, supplied by batteries.
• Cables: Typically have live, neutral, and earth wires; plastic insulation for safety.
• Potential Difference (Voltage): Shared among components in series, constant across components in parallel.

Charge and Energy

• Electric Current: Flow of electric charge; measured in coulombs (C).
• Calculating Charge: $Q = I \times t$ (Charge = Current × Time)
• Energy Transferred: $E = P \times t$ (Energy = Power × Time)
• Power Equations: $( P = IV )$; $( P = I^2 R )$; $( P = \frac{V^2}{R} )$.

The National Grid

• Transports electricity from power stations using a system of cables and transformers.
• Step-up Transformers: Increase voltage for efficient transmission.
• Step-down Transformers: Decrease voltage to safe levels at delivery points.

Efficiency

• Efficiency measures useful energy output against total input.
• Formulas:
  • Energy: $\text{Efficiency} = \frac{\text{Useful Output Energy}}{\text{Total Input Energy}}$
  • Power: $\text{Efficiency} = \frac{\text{Useful Power Output}}{\text{Total Power Input}}$
• Nothing is 100% efficient; energy losses due to various factors.

Energy Resources

Renewable Sources

• Solar, wind, hydroelectric, geothermal, wave power, biofuels.
• Advantages: Sustainable, reduce pollution, minimal operational costs.
• Disadvantages: Higher initial costs, space requirements, reliability issues.

Non-Renewable Sources

• Fossil fuels (coal, oil, gas); finite supply and environmental impact.
• Trends indicate a shift towards increasing renewable energy use.

Energy Stores and Transfers

Types of Energy Stores

• Kinetic, thermal, chemical, elastic potential, gravitational potential, electrostatic, magnetic, nuclear.
• Energy Transfer Methods: Mechanically, electrically, heating.

Conservation of Energy

• Energy cannot be created or destroyed, only transformed.
• Some energy is lost as waste during transfers.

Power

• Power is the rate of energy transfer: $P = \frac{E}{t}$ or $P = \frac{W}{t}$.
• Reducing friction with lubrication can help reduce wasted energy transferred to the environment.

Heat Transfer

• Conduction: Heat transfer through vibrations in solids.
• Convection: Heat transfer in fluids causing density changes and currents.
• Insulation: Reduces heat loss in buildings (e.g., double glazing, cavity walls).

Specific Energy Calculations

• Kinetic Energy ($E<em>k$): $E</em>k = \frac{1}{2} m v^2$ (where $m$ is mass and $v$ is speed).
• Gravitational Potential Energy ($E<em>p$): $E</em>p = m g h$ (where $m$ is mass, $g$ is gravitational field strength, and $h$ is height).
• Elastic Potential Energy ($E<em>e$): $E</em>e = \frac{1}{2} k e^2$ (where $k$ is the spring constant and $e$ is extension).
• Thermal Energy ($\Delta E$): $\Delta E = m c \Delta \theta$ (where $m$ is mass, $c$ is specific heat capacity, and $\Delta \theta$ is temperature change).
• Chemical Energy: Energy stored in chemical bonds; often calculated based on energy density and mass ($E = m \times \text{specific energy store}$) or energy transfer over time ($E = P \times t$).