Every Energy concept in the high school Science Bowl study set (grades 9-12), with a short definition for each. Read through them here, then drill them as flashcards or practise real Energy questions.
First Law of Thermodynamics: energy cannot be created or destroyed — only converted between forms. Total energy of an isolated system is constant. Forms include kinetic, gravitational potential, elastic potential, thermal, chemical, electrical, radiant, and nuclear energy.
Heavy nucleus (U-235, Pu-239) absorbs a neutron and splits into lighter nuclei + 2–3 neutrons + energy. Released neutrons can trigger more fissions (chain reaction). Requires critical mass. Used in nuclear reactors (controlled, moderated by water or graphite) and atomic bombs (uncontrolled).
Light nuclei (deuterium + tritium, hydrogen isotopes) combine to form helium-4 + a neutron + enormous energy. Releases ~3–4× more energy per mass than fission. Powers stars via the proton-proton chain. Requires extreme temperatures (>10⁷ K) to overcome Coulomb repulsion. Tokamak reactors pursue controlled fusion.
Coal (compressed ancient plants, highest carbon content, most CO₂/energy), petroleum (marine organisms; refined to gasoline, diesel, jet fuel), natural gas (mainly CH₄, cleanest-burning). All release CO₂ and other pollutants on combustion, driving the enhanced greenhouse effect. Non-renewable on human timescales.
Photons strike a silicon p-n junction semiconductor, exciting electrons across the band gap and producing direct current (DC). Inverters convert DC to AC. Typical panel efficiency: 15–22%. The photoelectric effect (Einstein, 1905) is the quantum basis. Output scales with light intensity and angle.
Wind turbines convert kinetic energy of wind to rotational energy via blades, then to electricity via generator. Betz limit: maximum theoretical efficiency = 59.3% (can never capture all wind energy). Offshore wind is stronger and more consistent. Power output scales with the cube of wind speed (P ∝ v³).
No heat engine can be 100% efficient (2nd Law). Carnot efficiency (maximum theoretical): η = 1 − Tc/Th (temperatures in Kelvin). Real engines are always less than Carnot. COP (coefficient of performance) for refrigerators: COP = Qc/W. For heat pumps: COP = Qh/W.
Converts gravitational PE of water to electricity via turbines and generators. Power P = ρghQ. Pumped-storage: pump water uphill when energy is cheap; release to generate on demand — acts as a grid-scale battery. Run-of-river vs reservoir (dam) types. Largest renewable electricity source globally.
Entropy of an isolated system always increases (or stays the same). Heat flows spontaneously from hot to cold. No process is 100% efficient — some energy is always lost as waste heat. Clausius statement: heat cannot spontaneously flow from cold to hot. Arrow of time is defined by entropy increase.
Conduction: heat transfer through direct contact; rate depends on thermal conductivity, area, temperature difference, and thickness (Fourier's Law). Convection: heat carried by fluid movement; drives ocean circulation and weather. Radiation: electromagnetic waves (infrared); requires no medium; described by Stefan-Boltzmann Law (P = σεAT⁴).
Heat from Earth's interior (radioactive decay + residual heat from formation). Used directly for heating or to generate electricity (steam drives turbines). Geothermal power plants require high-temperature geothermal reservoirs (e.g., Iceland, Kenya, Geysers in California). Baseload renewable — consistent output unlike solar/wind.
Harnesses energy from tidal changes in sea level. Tidal barrages: dam-like structures capture potential energy of tidal range. Tidal stream generators: underwater turbines in tidal currents (like underwater wind turbines). Predictable unlike solar/wind. Limited to coastal regions with large tidal ranges (e.g., Bay of Fundy).
Biomass: organic material (wood, crop waste, animal waste) burned directly or converted to biogas/biofuels. Ethanol: fermented from sugars/starches (corn, sugarcane). Biodiesel: made from vegetable oils/animal fats via transesterification. Biogas (mostly CH₄) from anaerobic digestion. Carbon-neutral if sustainably sourced.
Electrochemical device that converts H₂ and O₂ directly to electricity + water (2H₂ + O₂ → 2H₂O + electricity). Anode: H₂ oxidized, releases electrons. Cathode: O₂ reduced with electrons + H⁺. Efficiency ~40–60%, higher than combustion. Zero emissions at point of use. Hydrogen must be produced (electrolysis or steam reforming).
Lithium-ion batteries: Li⁺ ions move between anode (graphite) and cathode (LiCoO₂) through electrolyte. High energy density. Pumped hydro: largest grid storage. Flow batteries: electrolyte stored in tanks (scalable). Supercapacitors: fast charge/discharge, lower energy density. Storage critical for intermittent renewables.
Solar radiation (shortwave) passes through atmosphere and warms Earth's surface. Earth re-radiates longwave infrared radiation, which is absorbed and re-emitted by greenhouse gases (CO₂, CH₄, H₂O, N₂O, ozone). Enhanced greenhouse effect: human-emitted CO₂ from fossil fuels increases warming above natural levels.
CCS captures CO₂ from power plants or atmosphere and stores it underground in geological formations, depleted oil/gas fields, or mineralizes it. Direct air capture (DAC): pulls CO₂ directly from ambient air. Bioenergy with CCS (BECCS) could achieve negative emissions. High cost limits widespread deployment.
Unstable nuclei emit particles/energy spontaneously. Alpha (α): emits ²He nucleus (A−4, Z−2); stopped by paper. Beta-minus (β⁻): neutron → proton + electron; stopped by metal foil. Gamma (γ): high-energy photon; requires lead shielding. Half-life (t½): time for half the nuclei to decay; used in radiometric dating.
Joule (J): SI unit of energy. 1 calorie = 4.184 J. 1 kWh = 3.6×10⁶ J. 1 BTU ≈ 1055 J. 1 eV = 1.6×10⁻¹⁹ J. Power: 1 Watt = 1 J/s; 1 horsepower = 746 W. Energy content of fuels measured in MJ/kg (hydrogen: 142 MJ/kg; gasoline: 46 MJ/kg; coal: ~30 MJ/kg).
Power is transmitted at high voltage to minimize resistive losses (P_loss = I²R; high V → low I for same power). Step-up transformers increase voltage for transmission; step-down at substations reduce for consumers. AC (alternating current) used because transformers only work with AC. DC transmission used for some long-distance high-voltage links.
High-level waste (HLW): spent nuclear fuel; highly radioactive, requires deep geological disposal (stable for 10,000+ years). Low-level waste: contaminated tools/clothing. Spent fuel rods cooled in water pools first, then dry cask storage. Reprocessing extracts remaining fissile material (France, Russia) but creates proliferation concerns.
Efficiency = useful energy output / total energy input × 100%. LED bulbs: ~90% efficient (vs ~5% for incandescent). Electric vehicles: ~77% tank-to-wheel vs ~20% for gasoline. Insulation reduces conduction heat losses in buildings. ENERGY STAR ratings. Cogeneration (CHP): captures waste heat for useful heating.
Measure of disorder or randomness in a system (S, units: J/K). 2nd Law: ΔS_universe ≥ 0 for any process. Entropy increases when: ice melts, gas expands, heat flows from hot to cold. Mixing increases entropy. Boltzmann's definition: S = k·ln(W) where W is the number of microstates. Low entropy states are less probable.
Renewables replenish on human timescales: solar, wind, hydro, geothermal, tidal, biomass. Non-renewables: fossil fuels (coal, oil, gas) and nuclear (uranium is finite). Renewables have near-zero marginal fuel cost but high capital cost. Wind and solar have intermittency challenges requiring storage or backup. Global energy still ~80% from fossil fuels.
OTEC exploits temperature differences between warm surface water (~25°C) and cold deep water (~5°C) to run a heat engine. Low Carnot efficiency (~3–5%) but uses a continuous, renewable resource. Three types: closed-cycle (ammonia as working fluid), open-cycle (flash steam), hybrid. Best near tropical coastlines.
Nuclear reactors convert fission energy to electricity. Core components: fuel rods (enriched U-235 or Pu-239 pellets), moderator (slows neutrons to thermal energies; water, heavy water, or graphite), control rods (absorb neutrons; boron or cadmium; adjust reaction rate), coolant (removes heat; water, CO₂, or liquid sodium). Pressurized Water Reactor (PWR): most common; primary loop heats secondary loop via heat exchanger. Boiling Water Reactor (BWR): steam generated directly in core.
EVs use electric motors powered by lithium-ion battery packs (typically 40–100 kWh). Regenerative braking recovers kinetic energy as electricity. Energy efficiency: ~77% tank-to-wheel vs ~20% for gasoline ICE. Well-to-wheel emissions depend on electricity grid mix. Range anxiety: addressed by expanding charging infrastructure (Level 1/2 AC and Level 3 DC fast charging). Battery degradation: ~2% capacity loss per year. Solid-state batteries promise higher energy density.
Smart grid: modernized electricity network using digital communication to improve reliability and efficiency. Two-way communication between utilities and consumers. Advanced metering infrastructure (AMI): real-time usage monitoring and dynamic pricing. Demand response: consumers reduce load during peak periods in exchange for incentives. Enables integration of distributed renewables and EVs. Microgrids: self-sufficient local grids that can disconnect from main grid (island mode) during outages.
Four-stroke cycle (Otto cycle): intake (piston down, fuel-air mixture in), compression (piston up, mixture compressed), power (spark ignites mixture, piston driven down), exhaust (piston up, combustion gases expelled). Diesel cycle: fuel ignites by compression heat (no spark plug); higher compression ratio → higher efficiency (~45% vs ~25% for gasoline). Engine efficiency limited by Carnot theorem. Emissions: CO, NOₓ, hydrocarbons, CO₂, particulates. Catalytic converter reduces CO and NOₓ.
Seebeck effect: when two dissimilar conductors are joined and junction temperatures differ, a voltage is produced. V = S·ΔT where S = Seebeck coefficient. Peltier effect (reverse): current through junction creates temperature difference (used in cooling modules). Figure of merit ZT = S²σT/κ (σ = electrical conductivity; κ = thermal conductivity); high ZT materials are good thermoelectrics. Applications: spacecraft radioisotope thermoelectric generators (RTGs), waste heat recovery, wearable electronics.
Wave energy converters (WECs): oscillating water column (OWC) traps air above water surface; wave compresses air through turbine. Point absorbers: floating buoy drives hydraulic pump. Overtopping devices: wave runs up ramp into reservoir, water falls through turbine. Tidal stream generators: underwater turbines (like wind turbines) in tidal currents; predictable energy output. Tidal barrage: dam across estuary captures tidal range; generates electricity on ebb and flow. Limited by suitable sites.
Carbon footprint: total GHG emissions caused by an individual, organization, event, or product (measured in CO₂-equivalent). Life cycle assessment (LCA): cradle-to-grave analysis of environmental impacts, including manufacturing, use, and disposal. Scope 1: direct emissions. Scope 2: purchased electricity. Scope 3: value chain (supply chain, product use). GWP (Global Warming Potential): compares warming effect of GHGs over 100 years relative to CO₂ (CH₄ = 28 GWP; N₂O = 265 GWP).
LCOE = total lifetime costs / total lifetime energy produced ($/MWh). Accounts for capital costs (CAPEX), operating costs (OPEX), fuel costs, and financing. Allows comparison across technologies. Solar PV and onshore wind now have LCOE competitive with or below fossil fuels in many regions (~$30–50/MWh). Nuclear: high capital costs despite low fuel costs (~$90–130/MWh). Natural gas: low capital, variable fuel costs. Discount rate strongly affects LCOE of capital-intensive technologies.
Net zero: achieving a balance between GHG emissions produced and removed from the atmosphere. Requires: deep decarbonization of energy, transport, and industry; carbon removal (forests, BECCS, direct air capture). Carbon neutrality: offsetting remaining emissions with carbon credits or removals. Paris Agreement (2015): limit warming to 1.5–2°C above pre-industrial levels; 195+ countries. IPCC reports summarize climate science and mitigation pathways. Carbon trading: cap-and-trade systems put a price on emissions.
PEM (proton exchange membrane): uses solid polymer electrolyte; operates at ~80°C; used in vehicles and portable power. SOFC (solid oxide fuel cell): operates at 700–1000°C; high efficiency; used in stationary power; can use various fuels (H₂, methane). Alkaline fuel cell (AFC): used in spacecraft (Apollo); uses KOH electrolyte. Phosphoric acid fuel cell (PAFC): first commercial fuel cell. MCFC (molten carbonate): high temperature; suitable for industrial use. Efficiency typically 40–60%.
Pumped hydro storage (PHS): 90% of global grid storage capacity; pumps water uphill during low-demand periods, releases through turbines when needed. Round-trip efficiency ~70–85%. Flywheel energy storage: kinetic energy stored in rotating mass; charge/discharge in seconds; high power density, low energy density; used for frequency regulation. Compressed air energy storage (CAES): stores air in underground caverns under pressure; efficiency ~70%. All address intermittency of solar and wind.
First-generation PV: monocrystalline silicon (highest efficiency, ~22–26%), polycrystalline silicon (~17–20%). Second-generation thin films: CdTe (cadmium telluride, ~18%), CIGS (copper indium gallium selenide, ~23%). Third-generation: perovskite solar cells (rapidly improving, >29% in lab); multi-junction concentrator cells (>47% in lab). Shockley-Queisser limit: theoretical max efficiency for single-junction solar cell ~33%. Agrivoltaics: combining solar panels with agriculture.
Energy conservation for thermodynamic systems: ΔU = Q − W. ΔU = change in internal energy; Q = heat added to system (positive when absorbed); W = work done by system (positive when system expands). For ideal gas: U depends only on temperature (ΔU = nCᵥΔT). Isothermal process: ΔT = 0, ΔU = 0 → Q = W. Adiabatic: Q = 0 → ΔU = −W. Isochoric (constant volume): W = 0 → ΔU = Q. Isobaric (constant pressure): W = PΔV.
Piezoelectric effect: certain crystals (quartz, PZT) generate voltage when mechanically stressed; used in sensors, lighters, ultrasound, and energy harvesting from vibrations/footsteps. Magnetohydrodynamic (MHD) generators: conducting fluid (plasma or liquid metal) flows through magnetic field → induces EMF (no moving parts). Used experimentally in nuclear fusion containment and propulsion. Triboelectric nanogenerators: harvest energy from friction between surfaces.
Zeroth Law: if system A is in thermal equilibrium with B, and B is in equilibrium with C, then A is in equilibrium with C — establishes temperature as a measurable property. Celsius (°C): 0 = ice point, 100 = steam point at 1 atm. Kelvin (K): absolute scale, 0 K = absolute zero (−273.15°C); no negative values. Fahrenheit (°F): °F = (°C × 9/5) + 32. Rankine (°R): absolute Fahrenheit scale. Triple point of water: 273.16 K = 0.01°C (defines kelvin).