Energy Sources
Section: Motion, Forces & Energy | Syllabus: Cambridge AS Level Physics 9702
Energy from the Sun The Sun is the primary source of almost all energy on Earth, providing light and heat energy that drive many natural processes. Key Idea Nearly all energy sources on Earth (except geothermal and nuclear ) originate from the Sun.
Examples of Solar Energy Use Solar panels: Convert sunlight into electrical energy (solar cells) Solar water heaters: Use sunlight to heat water directly Photosynthesis: In plants converts solar energy into chemical energy stored in food and fuels Solar Energy Applications Diagram showing: (1) Solar panels on a roof converting sunlight directly to electricity.
(2) Solar water heater with dark tubes absorbing heat. (3) Arrows showing sunlight energy being captured and converted. Energy flow: Light → Electrical or Thermal energy. Limitation Solar energy is intermittent – it depends on sunlight, weather, and time of day, making it less reliable without energy storage systems.
Energy from Fuels Fuels contain chemical energy that can be released by burning (combustion). Types of Fuels Fossil fuels: Coal, oil, and natural gas – formed from dead plants and animals over millions of years Biofuels: Fuels made from recently living organisms (like ethanol, wood, or biodiesel) Energy transformation: Chemical → Heat → Kinetic or Electrical (in engines or power stations) Energy from Fuels Energy flow diagram: Fuel (Chemical Energy) → Combustion → Heat Energy → Steam turns turbine (Kinetic Energy) → Generator produces Electrical Energy.
CO₂ released as waste. Examples: coal, oil, natural gas power stations. Important Points Burning fuels releases carbon dioxide (CO₂) → contributes to global warming Fossil fuels are non-renewable – once used, they cannot be replaced quickly Advantage Fuels provide large amounts of energy on demand and are easy to transport and store.
Energy from Water Moving water can generate electricity in several ways. Water-Based Energy Sources Hydroelectric power: Water stored in a dam flows through turbines, converting GPE → KE → Electrical energy Tidal power: Uses the rise and fall of tides to move turbines Wave power: Harnesses the up-and-down motion of surface waves Hydroelectric Power Station Cross-section diagram: Dam holding water at height (GPE).
Water flows down through pipes to turbines at bottom (GPE → KE). Turbines connected to generators produce electricity. Water exits at lower level. Clean, renewable energy with no emissions. Limitations Requires suitable locations (large rivers or coastal areas), and can disrupt local ecosystems and habitats.
Key Advantage Water-based energy is renewable and does not produce greenhouse gases once built. Geothermal Energy Geothermal energy comes from heat stored beneath the Earth's surface, usually near volcanic areas.
Cold water is pumped into hot rocks underground, and the steam produced drives turbines to generate electricity. Geothermal Power Generation Cross-section diagram: Cold water pumped down through pipe into hot underground rocks (heated by radioactive decay in Earth's core).
Steam rises up separate pipe. Steam drives turbines connected to generator. Independent of Sun, available 24/7. What Makes It Unique Geothermal energy does not depend on the Sun – it comes from radioactive decay inside the Earth.
Limitations Only available in regions with volcanic or tectonic activity Initial setup costs are high Nuclear Energy Nuclear energy is released from changes in the nucleus of atoms. Types of Nuclear Reactions Nuclear fission: Splitting of large nuclei (e.g., uranium-235) into smaller ones, releasing huge amounts of energy Nuclear fusion: Joining of small nuclei (like hydrogen) to form a larger nucleus – this is how the Sun produces energy Nuclear Power Station Schematic diagram: Reactor core where nuclear fission of uranium-235 releases heat.
Heat transferred to water creating steam. Steam drives turbines connected to generators. Cooling towers release excess heat. Produces no CO₂ but creates radioactive waste. Key Concept Fission is used in nuclear power stations on Earth.
Fusion powers the Sun but is not yet practical for large-scale use on Earth. Nuclear Energy Issues Radioactive waste disposal is difficult and hazardous Accidents can cause serious contamination Advantage Produces large amounts of energy with no carbon emissions.
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