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Extremadura PAU General Sciences - independent foundations study materials
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Extremadura PAU General Sciences - independent foundations practice questions

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Question 1Scientific questions, evidence and quantitative reasoning

In a controlled scientific experiment designed to test the effect of temperature on enzymatic activity, what term describes the variable that the investigator systematically changes?

  1. Independent variable Correct answer.
  2. Dependent variable
  3. Controlled variable
  4. Confounding variable

Explanation

The independent variable is the factor intentionally manipulated or altered by the researcher (e.g., temperature) to observe its effect on the response variable.

Question 2Scientific questions, evidence and quantitative reasoning

Which of the following SI derived units is used to measure energy, work, and quantity of heat?

  1. Watt (W)
  2. Joule (J) Correct answer.
  3. Pascal (Pa)
  4. Newton (N)

Explanation

The Joule (J) is the SI unit of energy, work, and heat, defined as 1 J = 1 N·m = 1 kg·m²/s².

Question 3Scientific questions, evidence and quantitative reasoning

When plotting data where the dependent variable increases at a rate proportional to its current value, what type of mathematical relationship does the resulting curve demonstrate?

  1. Linear growth
  2. Inverse proportion
  3. Exponential growth Correct answer.
  4. Logarithmic decay

Explanation

Exponential growth occurs when the growth rate of a mathematical function is proportional to the function's current value, yielding a characteristic J-shaped curve.

Question 4Scientific questions, evidence and quantitative reasoning

Why is a placebo group included in clinical trials testing new pharmacological treatments?

  1. To increase the sample size without incurring chemical reagent costs
  2. To ensure all trial participants receive active therapeutic compounds
  3. To eliminate the need for statistical significance testing
  4. To isolate the physiological effect of the drug from psychological factors and baseline changes Correct answer.

Explanation

Placebos control for psychological expectations, participant reporting bias, and spontaneous recovery, isolating the specific pharmacological efficacy of the drug.

Question 5Scientific questions, evidence and quantitative reasoning

What is the primary difference between accuracy and precision in physical scientific measurements?

  1. Accuracy reflects proximity to the true value, whereas precision reflects repeatability of measurements Correct answer.
  2. Accuracy measures consistency across trials, whereas precision measures closeness to target
  3. Accuracy applies only to qualitative data, whereas precision applies to quantitative data
  4. Accuracy is affected by random errors, whereas precision is affected only by systematic bias

Explanation

Accuracy describes how close a measured value is to the true or accepted value, while precision describes the agreement among repeated measurements under unchanged conditions.

Question 6Scientific questions, evidence and quantitative reasoning

A student measures the mass of a chemical sample five times, obtaining 4.12 g, 4.11 g, 4.13 g, 4.12 g, and 4.12 g. The true reference mass is 4.50 g. How should these experimental results be characterized?

  1. High accuracy and high precision
  2. High accuracy and low precision
  3. Low accuracy and high precision Correct answer.
  4. Low accuracy and low precision

Explanation

The measured values are highly clustered together (range of 0.02 g, high precision), but they systematically deviate from the true value of 4.50 g (low accuracy), indicating systematic error.

Question 7Scientific questions, evidence and quantitative reasoning

In a double-blind study evaluating a new vaccine, which party is kept unaware of group assignments (vaccine vs. placebo)?

  1. Only the participants receiving the injections
  2. Only the healthcare staff administering the injections
  3. Only the bio-statistical analysis team evaluating data
  4. Both the study participants and the clinical staff conducting the trial Correct answer.

Explanation

In a double-blind trial, neither the participants nor the clinical experimenters know who receives the active treatment, preventing subconscious bias in treatment or evaluation.

Question 8Scientific questions, evidence and quantitative reasoning

A scatter plot displaying the relationship between atmospheric carbon dioxide concentration and global average surface temperature shows a correlation coefficient of r = +0.94. What does this statistical value indicate?

  1. A weak positive linear relationship proving direct single-factor causation
  2. A strong positive linear correlation between the two measured variables Correct answer.
  3. An inverse proportional relationship where CO2 lowers temperature
  4. That 94% of temperature variation is caused by measurement error

Explanation

A correlation coefficient r near +1 (+0.94) indicates a strong positive linear association between the two variables, though correlation alone does not automatically prove direct causation.

Question 9Scientific questions, evidence and quantitative reasoning

Which expression correctly converts a velocity of 90 km/h into SI base units (meters per second, m/s)?

  1. 90 × 3.6 = 324 m/s
  2. 90 / 60 = 1.5 m/s
  3. 90 / 3.6 = 25 m/s Correct answer.
  4. 90 × 1000 = 90,000 m/s

Explanation

To convert km/h to m/s, divide by 3.6 (90 km/h × (1000 m / 1 km) × (1 h / 3600 s) = 90 / 3.6 = 25 m/s).

Question 10Scientific questions, evidence and quantitative reasoning

What is the primary purpose of calculating standard deviation (σ) when evaluating a scientific data set?

  1. To identify the exact middle value of an ordered dataset
  2. To calculate the true mean value of an infinite population
  3. To eliminate outlier values from published research automatically
  4. To quantify the extent of variation or dispersion of data points around the mean Correct answer.

Explanation

Standard deviation measures how spread out individual data points are relative to the sample or population mean.

Question 11Scientific questions, evidence and quantitative reasoning

In scientific literature, what distinguishes a scientific theory from a scientific law?

  1. A theory provides an overarching explanatory model for phenomena, whereas a law describes concise mathematical relationships Correct answer.
  2. A theory is an unproven guess, whereas a law is an absolute permanent truth
  3. A theory becomes a law once it is verified by more than 100 experiments
  4. A theory applies only to biology, whereas a law applies only to physics and chemistry

Explanation

Scientific laws describe what happens (often via mathematical equations), while scientific theories explain why and how natural phenomena occur.

Question 12Scientific questions, evidence and quantitative reasoning

Which sampling method minimizes selection bias when conducting an epidemiological study across a diverse population?

  1. Convenience sampling at a local city hospital
  2. Random sampling where every individual has an equal probability of selection Correct answer.
  3. Voluntary response sampling via an online social media poll
  4. Purposive sampling selecting only individuals with identical exercise habits

Explanation

Simple random sampling ensures that every member of the target population has an equal chance of selection, eliminating systematic selection bias.

Question 13Scientific questions, evidence and quantitative reasoning

A commercial product claims to 'detoxify quantum cellular bio-energies' using proprietary crystals, but provides no empirical data, peer-reviewed studies, or testable mechanism. How should this claim be evaluated scientificially?

  1. As an established scientific breakthrough requiring immediate implementation
  2. As a valid alternative scientific theory protected by commercial secrecy
  3. As pseudoscience relying on technobabble and non-verifiable claims Correct answer.
  4. As a standard biomedical protocol approved by global health authorities

Explanation

The use of scientific-sounding buzzwords ('quantum cellular bio-energies') without testable mechanisms, open data, or peer review is characteristic of pseudoscience.

Question 14Scientific questions, evidence and quantitative reasoning

When analyzing a logarithmic scale graph of bacterial population growth over time, what does a straight line with a positive slope represent?

  1. Stationary population equilibrium where birth rate equals death rate
  2. Linear arithmetic growth where a constant number of cells is added per hour
  3. Decelerating growth due to nutrient exhaustion
  4. Exponential growth where the cell doubling time remains constant Correct answer.

Explanation

On a semi-logarithmic plot (log N vs time), exponential growth forms a straight line because logarithm transforms exponential functions into linear relationships.

Question 15Scientific questions, evidence and quantitative reasoning

An analytical sensor measures a gas concentration of 50.0 ppm. If the systematic uncertainty of the sensor is ±2.0% and the random measurement noise is ±0.5 ppm, what is the total absolute uncertainty interval of a single reading?

  1. ±1.5 ppm Correct answer.
  2. ±0.5 ppm
  3. ±2.5 ppm
  4. ±3.0 ppm

Explanation

Systematic uncertainty: 2.0% of 50.0 ppm = 1.0 ppm. Total absolute uncertainty is the sum of systematic and random components: 1.0 ppm + 0.5 ppm = ±1.5 ppm.

Question 16Scientific questions, evidence and quantitative reasoning

In a multi-variable environmental field trial investigating crop yield across regional microclimates, what statistical technique is used to test for significant differences among three or more treatment group means?

  1. Student's t-test for single pairs
  2. Analysis of Variance (ANOVA) Correct answer.
  3. Simple linear regression coefficient
  4. Chi-squared goodness-of-fit test

Explanation

Analysis of Variance (ANOVA) compares variance between multiple group means against variance within groups to evaluate if at least one group mean significantly differs.

Question 17Scientific questions, evidence and quantitative reasoning

What statistical risk occurs when a researcher performs multiple hypothesis tests on a single dataset without applying alpha-adjustment corrections (such as the Bonferroni correction)?

  1. Increased risk of Type II errors (false negatives)
  2. Reduction of statistical power to near zero
  3. Increased risk of Type I errors (false positives / false discovery) Correct answer.
  4. Complete loss of measurement precision in raw sensor data

Explanation

Running multiple independent significance tests at α = 0.05 increases the family-wise error rate, greatly elevating the chance of falsely rejecting a true null hypothesis (Type I error).

Question 18Scientific questions, evidence and quantitative reasoning

How does Thomas Kuhn's concept of a 'paradigm shift' describe revolutionary scientific advancement?

  1. As a steady, purely cumulative addition of factual data points without theoretical revisions
  2. As an abrupt change driven solely by political decisions of funding agencies
  3. As an instantaneous replacement of all physical laws every ten years
  4. As a transition where accumulated anomalies destabilize an existing paradigm, leading to a new conceptual framework Correct answer.

Explanation

Kuhn posited that science operates within a reigning paradigm until unresolvable anomalies accumulate, precipitating a crisis and a paradigm shift.

Question 19Matter, materials, reactions and chemical reasoning

What type of synthetic polymer can be repeatedly softened by heating and hardened by cooling without undergoing permanent chemical degradation?

  1. Thermoplastic polymer Correct answer.
  2. Thermosetting polymer
  3. Cross-linked vulcanized rubber
  4. Phenolic resin

Explanation

Thermoplastics (e.g., polyethylene, polypropylene) consist of linear or branched polymer chains held by weak intermolecular forces, allowing them to melt and re-mold repeatedly.

Question 20Matter, materials, reactions and chemical reasoning

What is a central goal of Green Chemistry as formulated by Paul Anastas and John Warner?

  1. Replacing all organic chemical reactions with high-temperature combustion
  2. Designing chemical products and processes that reduce or eliminate the use and generation of hazardous substances Correct answer.
  3. Maximizing the yield of chemical waste products to fill municipal landfills
  4. Mandating the use of non-recyclable heavy metals in consumer electronics

Explanation

Green Chemistry provides 12 principles focused on sustainable design: preventing waste, using non-toxic reagents, maximizing atom economy, and utilizing renewable feedstocks.

Question 21Matter, materials, reactions and chemical reasoning

Nanomaterials are defined as materials having at least one spatial dimension in what size range?

  1. 1 millimeter to 10 millimeters
  2. 100 micrometers to 1 millimeter
  3. 1 nanometer to 100 nanometers Correct answer.
  4. 1 meter to 10 meters

Explanation

Nanomaterials possess structural features or dimensions intentionally engineered within the nanoscale regime of 1 to 100 nanometers.

Question 22Matter, materials, reactions and chemical reasoning

Which physical property measures a material's ability to resist localized plastic deformation such as scratching, indentation, or abrasion?

  1. Ductility
  2. Electrical conductivity
  3. Thermal expansion coefficient
  4. Hardness Correct answer.

Explanation

Hardness (often measured via Mohs scale, Vickers, or Rockwell tests) quantifies resistance to localized surface indentation and scratch abrasion.

Question 23Matter, materials, reactions and chemical reasoning

In plastic resin identification codes, what polymer does Resin Code 1 (PET / PETE) signify?

  1. Polyethylene terephthalate Correct answer.
  2. High-density polyethylene
  3. Polyvinyl chloride
  4. Polystyrene

Explanation

RIC Code 1 designates Polyethylene Terephthalate (PET), widely used for beverage bottles and food containers due to its transparency and mechanical strength.

Question 24Matter, materials, reactions and chemical reasoning

How does adding a positive catalyst affect a chemical reaction at equilibrium?

  1. It increases the total yield of products by shifting equilibrium position to the right
  2. It accelerates both forward and reverse reaction rates equally by lowering the activation energy barrier (Ea) Correct answer.
  3. It increases the overall enthalpy change (ΔH) of the reaction
  4. It consumes reactant molecules permanently to generate light energy

Explanation

A catalyst speeds up reaction rates by offering an alternative pathway with lower activation energy (Ea). It does not shift equilibrium position or change ΔH or ΔG.

Question 25Matter, materials, reactions and chemical reasoning

In Green Chemistry metrics, how is Atom Economy calculated for a chemical synthesis reaction?

  1. (Volume of solvent consumed / Mass of final product) × 100
  2. (Actual practical yield of product / Theoretical max yield) × 100
  3. (Molar mass of desired product / Total molar mass of all reactants) × 100 Correct answer.
  4. (Energy consumed in Joules / Mass of waste disposed) × 100

Explanation

Atom Economy measures how efficiently raw material atoms are incorporated into the desired final product: Atom Economy = (Molar Mass of Desired Product / Sum of Molar Mass of All Reactants) × 100%.

Question 26Matter, materials, reactions and chemical reasoning

Which addition polymer is produced by the free-radical polymerization of tetrafluoroethylene (CF2=CF2)?

  1. Polypropylene (PP)
  2. Polyvinyl chloride (PVC)
  3. Low-density polyethylene (LDPE)
  4. Polytetrafluoroethylene (PTFE / Teflon) Correct answer.

Explanation

Polytetrafluoroethylene ([CF2-CF2]n) is synthesized from tetrafluoroethylene monomers, producing a hydrophobic material with high thermal stability and low friction.

Question 27Matter, materials, reactions and chemical reasoning

What unique phenomenon gives rise to novel quantum mechanical properties in quantum dots (semiconductor nanocrystals)?

  1. Quantum confinement: spatial restriction of charge carriers (electrons and holes) alters the electronic energy band gap Correct answer.
  2. Relativistic mass expansion of atomic nuclei under ambient light
  3. Spontaneous gravitational collapse of crystal lattices into micro black holes
  4. Frictional heating produced by molecular surface vibration

Explanation

When semiconductor dimensions drop below the exciton Bohr radius (<10 nm), quantum confinement discretizes energy levels, causing optical absorption/emission wavelengths to tune precisely with particle size.

Question 28Matter, materials, reactions and chemical reasoning

Which class of materials is characterized by high compressive strength, high thermal stability, and brittle fracture behavior due to ionic and covalent atomic bonds?

  1. Elastomers
  2. Ceramics Correct answer.
  3. Thermoplastic polymers
  4. Ductile metals

Explanation

Ceramics (e.g., alumina, silicon carbide) feature strong directional ionic/covalent bonds, yielding high melting points and hardness, but negligible dislocation movement, causing brittle failure.

Question 29Matter, materials, reactions and chemical reasoning

What chemical process describes depolymerization plastic recycling (feedstock/chemical recycling) compared to conventional mechanical recycling?

  1. Shredding plastic bottles into flakes and melting them directly into carpet fibers
  2. Landfilling plastic waste under high anaerobic soil compression
  3. Breaking polymer chains down chemically into original monomers or chemical feedstocks via hydrolysis, pyrolysis, or solvolysis Correct answer.
  4. Compacting mixed plastic waste into building foundation blocks

Explanation

Chemical recycling breaks covalent polymer backbones back into basic chemical monomers or hydrocarbons via thermochemical/solvolytic processes, allowing purification and re-polymerization into virgin plastics.

Question 30Matter, materials, reactions and chemical reasoning

What occurs when a metal undergoes work hardening (strain hardening) through cold rolling or mechanical deformation?

  1. Dislocation density decreases to zero, making the metal soft and flexible
  2. Thermal conductivity increases by a factor of 100
  3. The metal melts at room temperature due to lattice stress
  4. Dislocation density increases and dislocations entangle, increasing yield strength while reducing ductility Correct answer.

Explanation

Plastic deformation generates high dislocation densities. Interacting and entangling dislocations impede further dislocation movement, making the material harder and stronger but less ductile.

Question 31Matter, materials, reactions and chemical reasoning

Which condensation polymer is formed by the reaction between a dicarboxylic acid and a diol, releasing water molecules as a by-product?

  1. Polyester (e.g., PET) Correct answer.
  2. Polyethylene (PE)
  3. Polypropylene (PP)
  4. Polystyrene (PS)

Explanation

Polyesters are formed via condensation polymerization when carboxyl groups (-COOH) react with hydroxyl groups (-OH) to create ester linkages (-COO-) while eliminating H2O.

Question 32Matter, materials, reactions and chemical reasoning

Which supercritical fluid is widely utilized in industrial green chemistry as a non-toxic, non-flammable replacement for hazardous organic solvents in decaffeination and extraction?

  1. Supercritical benzene (C6H6)
  2. Supercritical carbon dioxide (scCO2) Correct answer.
  3. Supercritical carbon tetrachloride (CCl4)
  4. Supercritical diethyl ether

Explanation

Supercritical CO2 (above 31.1 °C and 73.9 bar) combines gas-like diffusivity with liquid-like solvent power, leaving zero toxic solvent residues upon depressurization.

Question 33Matter, materials, reactions and chemical reasoning

What single-atom-thick two-dimensional hexagonal lattice of sp2-hybridized carbon atoms exhibits extraordinary electrical conductivity, thermal conductivity, and mechanical tensile strength?

  1. Diamond
  2. Fullerene (C60)
  3. Graphene Correct answer.
  4. Amorphous carbon black

Explanation

Graphene is a single 2D layer of carbon atoms arranged in a honeycomb lattice, featuring delocalized π-electrons responsible for ballistic electron transport and supreme Young's modulus.

Question 34Matter, materials, reactions and chemical reasoning

What microstructural feature of composite materials (e.g., carbon-fiber-reinforced polymers) gives them exceptional strength-to-weight ratios?

  1. Extremely high density exceeding lead and gold
  2. Homogeneous single-phase metallic crystal lattice
  3. Complete absence of chemical interfaces between components
  4. High-strength reinforcement fibers embedded within a protective lightweight polymer matrix Correct answer.

Explanation

Composites combine high-tensile reinforcement fibers (carbon or glass fibers) that carry structural loads with a polymer resin matrix (epoxy) that binds fibers and transfers stress.

Question 35Matter, materials, reactions and chemical reasoning

A synthesis reaction uses 100 g of Reactant A (MW = 100 g/mol) and 100 g of Reactant B (MW = 100 g/mol) to produce 120 g of Desired Product C (MW = 120 g/mol) and 80 g of Waste By-product D (MW = 80 g/mol). What is the theoretical Atom Economy of this stoichiometric reaction?

  1. 60% Correct answer.
  2. 100%
  3. 40%
  4. 80%

Explanation

Atom Economy = (MW Product C / (MW Reactant A + MW Reactant B)) × 100% = (120 / (100 + 100)) × 100% = (120 / 200) × 100% = 60%.

Question 36Matter, materials, reactions and chemical reasoning

How does the degree of branching in polyethylene affect its macro-scale physical density and crystallinity?

  1. High branching increases chain packing density, forming High-Density Polyethylene (HDPE)
  2. High branching prevents linear polymer chains from packing tightly, lowering crystallinity and yielding Low-Density Polyethylene (LDPE) Correct answer.
  3. Branching converts polyethylene into a transparent inorganic ceramic
  4. Branching has zero effect on polymer density or crystallinity

Explanation

LDPE has frequent long- and short-chain branches that prevent polymer backbones from packing into crystalline lamellae, resulting in low density and flexibility, whereas unbranched HDPE packs tightly.

Question 37Matter, materials, reactions and chemical reasoning

In heterogeneous industrial catalysis, what operational mechanism causes catalyst 'poisoning'?

  1. The catalyst dissolves completely into gaseous product streams
  2. High pressure causes catalyst atomic nuclei to undergo radioactive decay
  3. Irreversible chemical chemisorption of impurity species (e.g., sulfur, lead) onto active catalyst surface sites, blocking reactant access Correct answer.
  4. Rapid growth of bacterial biofilms on catalyst surfaces at 600 °C

Explanation

Catalyst poisoning occurs when trace impurities form strong chemical bonds with active surface sites, permanently deactivating catalytic capability.

Question 38Matter, materials, reactions and chemical reasoning

Why do metallic gold nanoparticles (10–20 nm) exhibit intense ruby-red colors in liquid suspension, whereas bulk elemental gold appears metallic yellow?

  1. Gold nanoparticles absorb all visible light and re-emit monochromatic red laser light
  2. Nanoparticles undergo rapid chemical oxidation to red iron oxide (Fe2O3)
  3. Quantum chromodynamics causes subatomic quarks to emit red photons
  4. Localized Surface Plasmon Resonance (LSPR): collective oscillation of conduction electrons matching incoming green-blue light frequencies Correct answer.

Explanation

When light interacts with gold nanoparticles smaller than the light's wavelength, conduction electrons collectively oscillate in resonance with the incident electromagnetic field (LSPR), absorbing blue-green light and transmitting red light.

Question 39Forces, energy, fields, waves and modern physical models

What fundamental physical law states that energy cannot be created or destroyed, only transformed from one form to another?

  1. First Law of Thermodynamics (Conservation of Energy) Correct answer.
  2. Second Law of Thermodynamics (Entropy Increase)
  3. Third Law of Thermodynamics (Absolute Zero)
  4. Law of Definite Proportions

Explanation

The First Law of Thermodynamics establishes energy conservation: the total energy of an isolated system remains constant over time.

Question 40Forces, energy, fields, waves and modern physical models

How does a circular economy model differ fundamentally from a traditional linear economy model?

  1. Linear economies recycle all industrial waste; circular economies landfill all waste
  2. Linear economies follow 'take-make-dispose'; circular economies design out waste and keep materials in use Correct answer.
  3. Linear economies rely exclusively on solar energy; circular economies rely on coal
  4. Circular economies mandate single-use disposable packaging for hygienic safety

Explanation

Circular economies eliminate waste by designing products for durability, repair, reuse, and closed-loop material recycling, contrasting with the linear 'extract-produce-discard' model.

Question 41Forces, energy, fields, waves and modern physical models

According to the Second Law of Thermodynamics, why can no thermal heat engine ever achieve 100% efficiency when converting thermal energy into mechanical work?

  1. Friction in mechanical bearings creates new energy particles
  2. Heat flows spontaneously from cold reservoirs to hot reservoirs
  3. Some energy is inevitably dissipated as unavailable degraded thermal entropy to the environment Correct answer.
  4. Work cannot be converted back into thermal energy under any circumstances

Explanation

The Carnot principle and Second Law state that heat engine efficiency is bounded because some heat must always be rejected to a cold sink, increasing system entropy.

Question 42Forces, energy, fields, waves and modern physical models

What mechanism causes ocean acidification as atmospheric carbon dioxide concentrations rise?

  1. Increased solar radiation breaking down marine sodium chloride into hydrochloric acid
  2. Agricultural runoff dumping industrial nitric acid into coastal estuaries
  3. Thermal expansion forcing deep ocean sulfur compounds to dissolve into surface waters
  4. Dissolution of CO2 in seawater forming carbonic acid (H2CO3), which dissociates into H+ ions Correct answer.

Explanation

Seawater absorbs atmospheric CO2: CO2 + H2O ⇌ H2CO3 ⇌ HCO3- + H+. The release of H+ ions lowers pH and reduces available carbonate ions, harming calcifying organisms.

Question 43Forces, energy, fields, waves and modern physical models

What is the primary operational challenge associated with grid integration of high percentages of wind and solar power?

  1. Intermittency and variability dependent on weather conditions requiring energy storage and grid balancing Correct answer.
  2. Excessive emission of greenhouse gases during electricity generation
  3. High water consumption compared to thermoelectric cooling towers
  4. Complete inability to operate during daytime hours

Explanation

Solar and wind generation fluctuate with sunlight and wind speeds (intermittency), necessitating utility-scale battery storage, pumped hydro, or grid demand response to maintain voltage stability.

Question 44Forces, energy, fields, waves and modern physical models

What biofuel gas mixture, composed primarily of methane (CH4) and carbon dioxide (CO2), is produced by the anaerobic digestion of organic municipal waste?

  1. Syngas
  2. Biogas Correct answer.
  3. Liquefied petroleum gas (LPG)
  4. Compressed natural gas (CNG)

Explanation

Anaerobic digestion of organic biomass by methanogenic Archaea yields biogas, typically comprising 50–70% CH4 and 30–50% CO2, which can be scrubbed into biomethane.

Question 45Forces, energy, fields, waves and modern physical models

In a hydroelectric power station, what is the sequence of energy transformations that generates grid electricity?

  1. Chemical energy → Thermal energy → Nuclear energy → Electrical energy
  2. Solar radiation → Nuclear fission → Kinetic energy → Electrical energy
  3. Gravitational potential energy → Kinetic energy of water → Mechanical energy of turbine → Electrical energy Correct answer.
  4. Thermal energy → Elastic potential energy → Chemical energy → Electrical energy

Explanation

Water impounded at height possesses gravitational potential energy, which converts to kinetic energy as it descends, driving turbine blades (mechanical energy) to rotate an electromagnetic generator (electrical energy).

Question 46Forces, energy, fields, waves and modern physical models

What environmental hazard occurs when rainwater percolates through unlined solid waste landfills, absorbing toxic heavy metals and organic pollutants?

  1. Eutrophication
  2. Leachate formation Correct answer.
  3. Acid rain precipitation
  4. Thermal stratification

Explanation

Leachate is the contaminated liquid generated when water trickles through waste deposits, picking up dissolved or suspended matter that can contaminate groundwater if uncontained.

Question 47Forces, energy, fields, waves and modern physical models

Which energy conversion principle powers a concentrated solar power (CSP) parabolic trough plant?

  1. Photovoltaic electron excitation across a silicon p-n semiconductor junction
  2. Direct nuclear synthesis of helium from solar hydrogen rays
  3. Mirrors focus solar energy onto a receiver pipe to heat a fluid, generating steam to drive a conventional turbine Correct answer.
  4. Thermoelectric Peltier cooling generating direct current across metallic junctions

Explanation

CSP systems use curved mirrors to focus direct sunlight onto receiver tubes containing thermal heat transfer fluids, producing high-temperature steam for electricity generators.

Question 48Forces, energy, fields, waves and modern physical models

In industrial ecology, what is the term for a system where waste or by-products of one manufacturing process become the raw material input for another adjacent facility?

  1. Linear cradle-to-grave manufacturing
  2. Monoculture resource extraction
  3. Planned obsolescence
  4. Industrial symbiosis Correct answer.

Explanation

Industrial symbiosis involves geographic clustering of industries that trade materials, energy, water, and by-products, converting one facility's waste stream into another's valuable input.

Question 49Forces, energy, fields, waves and modern physical models

A thermodynamic heat pump consumes 2.0 kW of electrical power to transfer 8.0 kW of thermal energy into a building interior. What is the Coefficient of Performance (COP_heating) of this heat pump?

  1. 4.0 Correct answer.
  2. 0.25
  3. 2.0
  4. 6.0

Explanation

COP_heating = Q_out / W_in = 8.0 kW / 2.0 kW = 4.0. Heat pumps deliver more thermal energy than the electrical work consumed because they transfer ambient environmental heat.

Question 50Forces, energy, fields, waves and modern physical models

During pyrolytic thermal waste treatment, how does pyrolysis differ fundamentally from conventional municipal waste incineration?

  1. Pyrolysis uses pure oxygen at 3000 °C to create glass slag
  2. Pyrolysis relies on biological fungi to degrade plastics into compost
  3. Pyrolysis thermal decomposition occurs in the total absence of atmospheric oxygen Correct answer.
  4. Pyrolysis converts solid waste into radioactive isotopes for energy storage

Explanation

Pyrolysis is the endothermic thermal degradation of organic matter at elevated temperatures (400–800 °C) in an oxygen-free atmosphere, producing bio-char, bio-oil, and combustible syngas without direct combustion.