PHYSICS FORM SIX
Physics Form 6 Notes – Advanced Environmental & Electricity Physics Form 6 I. Environmental Physics 1.0 Introduction 1.1 Agriculture Physics 1.2 Human Survival 1.3 Renewable Energy 1.4 Built Environment 1.5 Remote Sensing 1.6 Geophysics 1.7 Pollution II. Current Electricity 2.1 Drift Velocity 2.2 Current Density 2.3 Resistance & Ohm’s Law 2.4 Temp. Coefficient Interactive & Lab Lab: Drift Velocity ACSEE Problems 1.0 Environmental Physics Definition: Environmental physics is an interdisciplinary field integrating physical processes in the Atmosphere, Biosphere, Hydrosphere, and Geosphere. It studies the response of living organisms to their environment. The environment is structured within the relationship between: Atmosphere: The gaseous envelope surrounding the Earth. Hydrosphere: All water bodies including oceans, rivers, and groundwater. Lithosphere (Geosphere): The solid Earth, rocks, and soil. Biosphere: The zone where life exists, interacting with all other spheres. 1.1 Agriculture Physics Agriculture physics applies physical principles to soil, plant, and atmospheric systems to optimize food production. A. Solar Radiation & Plant Growth Photosynthetically Active Radiation (PAR): Plants utilize light in the 400-700 nm range. The intensity of radiation determines the rate of photosynthesis. Phototropism: Growth towards light. Photoperiodism: Response to the length of day/night cycles (flowering). B. Wind, Air Temperature & Rainfall Wind: Increases transpiration rate by removing the boundary layer of saturated air from leaves. Mechanical stress from wind also strengthens stems (thigmomorphogenesis). Air Temperature: Dictates the rate of biochemical reactions (enzyme activity). Every plant has a minimum, optimum, and maximum temperature for growth ($T_{min}, T_{opt}, T_{max}$). Rainfall: Provides water for turgidity, nutrient transport, and photosynthesis electrons. C. Soil Physics Soil physics deals with the physical properties of soil that influence plant growth: Soil Texture & Structure: Determines porosity and aeration. Soil Water Potential: Governs how easily plants can extract water. Thermal Properties: Soil heat capacity controls how fast soil warms up in spring. Dark soils absorb more heat than light soils (Albedo effect). 1.2 Human Survival Physics Humans are homeotherms, maintaining a relatively constant body temperature (~37°C) despite environmental changes. Physics governs this thermal regulation. The Energy Balance Equation $$ S = M – W \pm R \pm C – E $$ \(S\) = Heat storage rate (W) \(M\) = Metabolic rate (Heat production) \(W\) = Mechanical work done by the body \(R\) = Radiation heat exchange \(C\) = Convection heat exchange \(E\) = Evaporation heat loss (Sweating) Heat Exchange Mechanisms Metabolism ($M$): The biochemical process of converting food into energy. Basal Metabolic Rate (BMR) is the energy required at rest. Radiation ($R$): Transfer of heat via electromagnetic waves. Depends on the temperature difference between skin and surroundings ($R \propto T_{skin}^4 – T_{env}^4$). Convection ($C$): Heat loss to air or water moving across the skin. Wind chill factor increases convection loss. Evaporation ($E$): The most effective cooling mechanism in hot environments. Latent heat of vaporization ($L_v$) removes heat as sweat turns to vapor. 1.3 Energy from the Environment Renewable energy physics focuses on converting natural energy flows into useful work. Photovoltaic (PV) Converts photon energy ($E=hf$) into electrical current using PN-junction semiconductors. Efficiency depends on band-gap energy and temperature. Wind Power Power extracted is proportional to the cube of wind speed: $$ P = \frac{1}{2} \rho A v^3 $$ where $\rho$ is air density and $A$ is rotor area. Geothermal Utilizes radioactive decay heat from the Earth’s core. Operates via steam turbines driven by hydrothermal reservoirs. Wave Energy Captures kinetic and potential energy of ocean waves. Wave power density depends on wave height squared ($H^2$) and period ($T$). 1.4 Built Environment & Remote Sensing The Built Environment Physics applied to human-made structures. Key concepts involve heat transfer and comfort. Thermal Comfort: Dependent on air temperature, radiant temperature, humidity, and air velocity. U-Value: Measure of thermal transmittance through walls. Lower U-values mean better insulation ($Rate = U \cdot A \cdot \Delta T$). Natural Ventilation: Using pressure differences caused by wind (Bernoulli’s principle) and stack effect (warm air rising) to cool buildings. Remote Sensing The acquisition of information about an object without making physical contact, typically via satellite or aircraft. Physics Principle: It relies on the detection of Electromagnetic Radiation (EMR) reflected or emitted from the Earth’s surface. Different surfaces (water, soil, vegetation) have distinct Spectral Signatures. Active Sensors: Emit their own energy (e.g., Radar, LiDAR). Passive Sensors: Detect natural energy (Sunlight) reflected (e.g., Photography, Landsat). 1.6 Geophysics (Seismology) Seismology is the study of earthquakes and the propagation of elastic waves through the Earth. Elastic Rebound Theory Explains earthquake generation: Tectonic forces deform rocks. When stress exceeds rock strength, rupture occurs, and rocks “rebound” to an unstrained position, releasing energy as seismic waves. Seismic Waves Classification Type Name Nature Characteristics Body P-Waves Longitudinal Fastest ($~8 km/s$). Pass through solids, liquids, gases. Body S-Waves Transverse Slower ($~4.5 km/s$). Cannot pass through liquids (Outer Core). Surface L-Waves Complex Slowest. Travel along surface. Cause most structural damage. Shadow Zones: The S-wave shadow zone (103° to 103°) provides the primary evidence that the Earth’s Outer Core is liquid, as S-waves cannot penetrate it. 1.7 Environmental Pollution Transport Mechanisms How pollutants move in the atmosphere: Advection: Horizontal transport of pollutants by wind. Diffusion: Spreading of pollutants from high to low concentration due to turbulence. Deposition: Removal of pollutants via rain (Wet deposition) or gravity (Dry deposition). Optical Properties & Visibility Pollution affects how light travels through the atmosphere, reducing visibility. Scattering: Particulates (aerosols) scatter light. Mie Scattering occurs when particles are similar in size to the wavelength of light (causing white smog). Rayleigh Scattering affects smaller molecules (blue sky). Absorption: Some pollutants (like soot or $NO_2$) absorb light, causing dark smoke or brownish haze. Nuclear Waste Radioactive waste management involves shielding and isolation. High-Level Waste (HLW): Spent fuel. Requires cooling and deep geological disposal. Half-life ($T_{1/2}$): The time taken for radioactivity to drop to half. Waste must be stored for multiple half-lives. 2.0 Current Electricity 2.1 Drift Velocity Theory In a conductor, free electrons move randomly. When an electric field $E$ is applied, they acquire a slow average velocity component called Drift Velocity ($v_d$). Derivation of \(I =