Free Grade 12 Physical Sciences practice questions covering Paper 1 (Physics) and Paper 2 (Chemistry) with full explanations.
Physical Sciences is one of the most valuable matric subjects for future study in engineering, medicine, and applied science — and one of the most conceptually demanding. Tour practice set covers both Physics (Paper 1) and Chemistry (Paper 2): mechanics, waves and sound, electricity and magnetism, chemical change, organic chemistry, and electrochemistry. Questions are written at NSC difficulty level with full mark-scheme-style explanations.
Where a calculation is involved, the explanation shows each step of the working — not just the final answer. Where a conceptual question is involved, the explanation connects the correct answer to the underlying principle. Tour is how you build the kind of understanding that transfers to unseen questions.
Physical Sciences consists of Paper 1 (Physics) and Paper 2 (Chemistry), each 3 hours and 150 marks. Essential for engineering, medicine, and science careers.
Key tip: Always convert units before substituting into equations. Mass to kg, temperature to Kelvin, volume to litres.
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correct answers
Question 01 of 20
Newton's Second Law formula?
Explanation: F=ma. Force in Newtons, mass in kg, acceleration in m/s^2.
Question 02 of 20
Ohm's Law?
Explanation: V=IR (voltage=current x resistance).
Question 03 of 20
Kinetic energy formula?
Explanation: KE=0.5mv^2. Mass in kg, velocity in m/s.
Explanation: In a closed system: total momentum before = total momentum after.
Question 16 of 20
Charles' Law at constant pressure?
Explanation: Charles' Law: V1/T1=V2/T2 at constant pressure. T must be in Kelvin.
Question 17 of 20
Half-life of radioactive isotope?
Explanation: Half-life: time for half the radioactive atoms to decay.
Question 18 of 20
Work done formula?
Explanation: W=Fd*cos(theta). F=force, d=displacement, theta=angle between them.
Question 19 of 20
Type of radiation stopped by paper?
Explanation: Alpha particles: stopped by paper or skin. Beta by aluminium. Gamma by lead.
Question 20 of 20
Ideal gas law?
Explanation: PV=nRT where P=pressure, V=volume, n=moles, R=8.314, T=Kelvin.
Q21
What is Newton's third law?
Explanation: Newton's 3rd Law: If A exerts force on B, B exerts equal and opposite force on A. Pairs always act on different objects. Walking: foot pushes back on ground, ground pushes foot forward.
Q22
What is the relationship between wavelength and frequency?
Explanation: Wave equation: v = fλ. v = wave speed (m/s), f = frequency (Hz), λ = wavelength (m). Speed is constant for a medium. Higher frequency → shorter wavelength. Light: f = c/λ.
Q23
What is work in physics?
Explanation: Work: W = Fd cosθ. θ is angle between force and displacement. Zero work: force perpendicular to displacement (holding a bag while walking). Negative work: force opposes motion (friction, braking).
Q24
What is the conservation of energy?
Explanation: Law of Conservation of Energy: total energy is constant. Potential energy converts to kinetic and vice versa. Friction: kinetic energy → heat. In closed system: ΣE = constant. Real systems: some energy always lost to heat (thermodynamics).
Q25
What is electric current?
Explanation: Electric current (I): charge (Q, Coulombs) per time (t, seconds). I = Q/t. In metals: electrons flow (opposite to conventional current direction). Direct current (DC): one direction. Alternating current (AC): direction alternates periodically.
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Q26
What is the difference between series and parallel circuits?
Explanation: Series: V_total = V₁+V₂+V₃. I = same throughout. R_total = R₁+R₂+R₃. Parallel: I_total = I₁+I₂+I₃. V = same across each branch. 1/R_total = 1/R₁+1/R₂+1/R₃.
Q27
What is the electromagnetic force?
Explanation: Four fundamental forces: Gravity (weakest, infinite range), Electromagnetic (light, chemistry, electricity — infinite range), Weak nuclear (radioactive decay), Strong nuclear (holds nucleus together — strongest, very short range).
Q28
What is radioactive decay?
Explanation: Radioactive decay types: Alpha (α): helium nucleus emitted, loses 2 protons+2 neutrons. Beta (β): neutron converts to proton, electron emitted. Gamma (γ): high-energy photon emitted, no mass change. Half-life: time for half of nuclei to decay.
Q29
What is the mole concept in chemistry?
Explanation: Mole: n = m/M. n = moles, m = mass (g), M = molar mass (g/mol). 1 mol O₂ = 32g = 6.022×10²³ molecules. Avogadro's number: 6.022×10²³. Used to count atoms and molecules.
Q30
What is acid-base neutralisation?
Explanation: Neutralisation: acid + base → salt + water. Example: HCl + NaOH → NaCl + H₂O. Strong acid + strong base: pH 7 product. Indicators: change colour at different pH values. Titration: precise neutralisation to determine concentration.
Q31
What is momentum?
Explanation: Momentum p = mv. Vector quantity (has direction). Law of Conservation of Momentum: total momentum before collision = total momentum after (in isolated system). Impulse = change in momentum = F×Δt.
Q32
What is a chemical bond?
Explanation: Ionic bond: metal gives electrons to non-metal (NaCl). Covalent bond: non-metals share electrons (H₂O, CO₂). Metallic bond: positive metal ions in 'sea' of delocalised electrons (conductivity, malleability). Intermolecular forces: between molecules (H-bonds, Van der Waals).
Q33
What is temperature vs heat?
Explanation: Temperature: intensive property (doesn't depend on amount). Heat: extensive property (depends on amount). Specific heat capacity: energy to raise 1kg by 1°C. Q = mcΔT. Thermal equilibrium: heat transfer stops when temperatures equal.
Q34
What is the difference between nuclear fission and fusion?
Explanation: Fission: U-235 + neutron → smaller nuclei + 2-3 neutrons + energy. Chain reaction. Used: nuclear reactors, atomic bombs. Fusion: H + H → He + energy. Powers stars. Requires extreme temperatures. Fusion produces far more energy per kg and less waste.
Q35
What are the states of matter?
Explanation: States of matter: Solid: particles vibrate in fixed positions. Liquid: particles flow but volume fixed. Gas: particles move freely, fill container. Plasma: extremely hot ionised gas (stars, lightning). Changes of state involve energy (latent heat).
Q36
What is the difference between speed and velocity?
Explanation: Speed: total distance / time (scalar). Velocity: displacement / time (vector). An object moving in a circle at constant speed has changing velocity (direction changes). Average vs instantaneous speed/velocity.
Q37
What is Charles's Law?
Explanation: Charles's Law: V₁/T₁ = V₂/T₂ (T in Kelvin). At constant pressure: double temperature → double volume. Combined with Boyle's Law and Gay-Lussac's Law → Ideal Gas Law: PV = nRT.
Q38
What is Boyle's Law?
Explanation: Boyle's Law: P₁V₁ = P₂V₂ (T constant). Double pressure → half volume. Named after Robert Boyle (1662). Applies to ideal gases. Real gases deviate at high pressure/low temperature.
Q39
What is the photoelectric effect?
Explanation: Photoelectric effect (Einstein, 1905): photons with energy E = hf strike metal. If E ≥ work function (φ), electrons emitted. Increasing intensity increases number of electrons but not their energy. Increasing frequency increases electron energy. Proved light is quantised.
Q40
What is the half-life of a radioactive substance?
Explanation: Half-life (t½): after 1 t½, N/2 remain. After 2 t½, N/4. After n half-lives: N × (1/2)ⁿ. Examples: Carbon-14 t½ = 5,730 years (radiocarbon dating). Uranium-235 t½ = 704 million years. Used in medicine, archaeology, geology.
Q41
What are electromagnetic waves?
Explanation: EM waves: transverse, travel at c = 3×10⁸ m/s in vacuum. All carry energy. No medium required. Visible light: 400-700nm wavelength. Radio: longest wavelength. Gamma: shortest wavelength, highest energy, most penetrating.
Q42
What is the ideal gas law?
Explanation: Ideal gas law: PV = nRT. Combines Boyle's, Charles's, and Avogadro's laws. Ideal gas: no intermolecular forces, negligible particle volume. Real gases approximate ideal at low pressure, high temperature.
Q43
What is oxidation and reduction (redox)?
Explanation: OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). Oxidation number increases: oxidised. Decreases: reduced. Oxidising agent: oxidises others, gets reduced itself. Reducing agent: reduces others, gets oxidised. Fe → Fe³⁺ + 3e⁻ (oxidation).
Q44
What is specific heat capacity?
Explanation: Specific heat capacity (c): water c = 4,200 J/kg·K (high — explains oceans moderate climate). Iron c = 450 J/kg·K. Q = mcΔT: Q = heat energy (J), m = mass (kg), c = specific heat, ΔT = temperature change. Higher c → more energy to heat up.
Q45
What is a catalyst?
Explanation: Catalyst: not consumed, not appear in balanced equation. Lowers activation energy. Examples: Pt in catalytic converters, enzymes (biological catalysts), Fe in Haber process (NH₃ synthesis). Inhibitor: slows reaction.
Q46
What is the Doppler effect?
Explanation: Doppler effect: source approaching → observed frequency higher (shorter wavelength). Source moving away → lower frequency (longer wavelength). Applications: radar speed guns, medical ultrasound, redshift in astronomy (universe expanding). Named after Christian Doppler (1842).
Q47
What is centripetal force?
Explanation: Centripetal force: directed toward centre, not a new type of force — can be gravity, tension, normal force, friction, or any combination. F = mv²/r. Centrifugal force: apparent outward force felt in rotating frame (not a real force in inertial frame).
Q48
What is Coulomb's law?
Explanation: Coulomb's law: F = kq₁q₂/r². k = 9×10⁹ N·m²/C². Same form as Newton's gravity but: can be repulsive (same sign charges), electromagnetic force far stronger than gravity. Charge measured in Coulombs (C).
Q49
What is power in physics?
Explanation: Power P = W/t. 1 Watt = 1 Joule/second. Electrical power: P = VI = I²R = V²/R. Mechanical power: P = Fv. Kilowatt-hour (kWh): energy unit on electricity bill (1 kW for 1 hour = 3.6 MJ).
Q50
What is the difference between conductor and insulator?
Explanation: Conductors: metals (Cu, Al, Ag best), graphite, ionic solutions. Semiconductors: Si, Ge — conductivity between. Insulators: rubber, plastic, glass, ceramic, dry air. Semiconductors form basis of all electronics (transistors, chips).
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Q51
What is Newton's third law?
Explanation: Newton's 3rd Law: If A exerts force on B, B exerts equal and opposite force on A. Pairs always act on different objects. Walking: foot pushes back on ground, ground pushes foot forward.
Q52
What is the relationship between wavelength and frequency?
Explanation: Wave equation: v = fλ. v = wave speed (m/s), f = frequency (Hz), λ = wavelength (m). Speed is constant for a medium. Higher frequency → shorter wavelength. Light: f = c/λ.
Q53
What is work in physics?
Explanation: Work: W = Fd cosθ. θ is angle between force and displacement. Zero work: force perpendicular to displacement (holding a bag while walking). Negative work: force opposes motion (friction, braking).
Q54
What is the conservation of energy?
Explanation: Law of Conservation of Energy: total energy is constant. Potential energy converts to kinetic and vice versa. Friction: kinetic energy → heat. In closed system: ΣE = constant. Real systems: some energy always lost to heat (thermodynamics).
Q55
What is electric current?
Explanation: Electric current (I): charge (Q, Coulombs) per time (t, seconds). I = Q/t. In metals: electrons flow (opposite to conventional current direction). Direct current (DC): one direction. Alternating current (AC): direction alternates periodically.
Q56
What is the difference between series and parallel circuits?
Explanation: Series: V_total = V₁+V₂+V₃. I = same throughout. R_total = R₁+R₂+R₃. Parallel: I_total = I₁+I₂+I₃. V = same across each branch. 1/R_total = 1/R₁+1/R₂+1/R₃.
Q57
What is the electromagnetic force?
Explanation: Four fundamental forces: Gravity (weakest, infinite range), Electromagnetic (light, chemistry, electricity — infinite range), Weak nuclear (radioactive decay), Strong nuclear (holds nucleus together — strongest, very short range).
Q58
What is radioactive decay?
Explanation: Radioactive decay types: Alpha (α): helium nucleus emitted, loses 2 protons+2 neutrons. Beta (β): neutron converts to proton, electron emitted. Gamma (γ): high-energy photon emitted, no mass change. Half-life: time for half of nuclei to decay.
Q59
What is the mole concept in chemistry?
Explanation: Mole: n = m/M. n = moles, m = mass (g), M = molar mass (g/mol). 1 mol O₂ = 32g = 6.022×10²³ molecules. Avogadro's number: 6.022×10²³. Used to count atoms and molecules.
Q60
What is acid-base neutralisation?
Explanation: Neutralisation: acid + base → salt + water. Example: HCl + NaOH → NaCl + H₂O. Strong acid + strong base: pH 7 product. Indicators: change colour at different pH values. Titration: precise neutralisation to determine concentration.
Q61
What is momentum?
Explanation: Momentum p = mv. Vector quantity (has direction). Law of Conservation of Momentum: total momentum before collision = total momentum after (in isolated system). Impulse = change in momentum = F×Δt.
Q62
What is a chemical bond?
Explanation: Ionic bond: metal gives electrons to non-metal (NaCl). Covalent bond: non-metals share electrons (H₂O, CO₂). Metallic bond: positive metal ions in 'sea' of delocalised electrons (conductivity, malleability). Intermolecular forces: between molecules (H-bonds, Van der Waals).
Q63
What is temperature vs heat?
Explanation: Temperature: intensive property (doesn't depend on amount). Heat: extensive property (depends on amount). Specific heat capacity: energy to raise 1kg by 1°C. Q = mcΔT. Thermal equilibrium: heat transfer stops when temperatures equal.
Q64
What is the difference between nuclear fission and fusion?
Explanation: Fission: U-235 + neutron → smaller nuclei + 2-3 neutrons + energy. Chain reaction. Used: nuclear reactors, atomic bombs. Fusion: H + H → He + energy. Powers stars. Requires extreme temperatures. Fusion produces far more energy per kg and less waste.
Q65
What are the states of matter?
Explanation: States of matter: Solid: particles vibrate in fixed positions. Liquid: particles flow but volume fixed. Gas: particles move freely, fill container. Plasma: extremely hot ionised gas (stars, lightning). Changes of state involve energy (latent heat).
Q66
What is the difference between speed and velocity?
Explanation: Speed: total distance / time (scalar). Velocity: displacement / time (vector). An object moving in a circle at constant speed has changing velocity (direction changes). Average vs instantaneous speed/velocity.
Q67
What is Charles's Law?
Explanation: Charles's Law: V₁/T₁ = V₂/T₂ (T in Kelvin). At constant pressure: double temperature → double volume. Combined with Boyle's Law and Gay-Lussac's Law → Ideal Gas Law: PV = nRT.
Q68
What is Boyle's Law?
Explanation: Boyle's Law: P₁V₁ = P₂V₂ (T constant). Double pressure → half volume. Named after Robert Boyle (1662). Applies to ideal gases. Real gases deviate at high pressure/low temperature.
Q69
What is the photoelectric effect?
Explanation: Photoelectric effect (Einstein, 1905): photons with energy E = hf strike metal. If E ≥ work function (φ), electrons emitted. Increasing intensity increases number of electrons but not their energy. Increasing frequency increases electron energy. Proved light is quantised.
Q70
What is the half-life of a radioactive substance?
Explanation: Half-life (t½): after 1 t½, N/2 remain. After 2 t½, N/4. After n half-lives: N × (1/2)ⁿ. Examples: Carbon-14 t½ = 5,730 years (radiocarbon dating). Uranium-235 t½ = 704 million years. Used in medicine, archaeology, geology.
Q71
What are electromagnetic waves?
Explanation: EM waves: transverse, travel at c = 3×10⁸ m/s in vacuum. All carry energy. No medium required. Visible light: 400-700nm wavelength. Radio: longest wavelength. Gamma: shortest wavelength, highest energy, most penetrating.
Q72
What is the ideal gas law?
Explanation: Ideal gas law: PV = nRT. Combines Boyle's, Charles's, and Avogadro's laws. Ideal gas: no intermolecular forces, negligible particle volume. Real gases approximate ideal at low pressure, high temperature.
Q73
What is oxidation and reduction (redox)?
Explanation: OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). Oxidation number increases: oxidised. Decreases: reduced. Oxidising agent: oxidises others, gets reduced itself. Reducing agent: reduces others, gets oxidised. Fe → Fe³⁺ + 3e⁻ (oxidation).
Q74
What is specific heat capacity?
Explanation: Specific heat capacity (c): water c = 4,200 J/kg·K (high — explains oceans moderate climate). Iron c = 450 J/kg·K. Q = mcΔT: Q = heat energy (J), m = mass (kg), c = specific heat, ΔT = temperature change. Higher c → more energy to heat up.
Q75
What is a catalyst?
Explanation: Catalyst: not consumed, not appear in balanced equation. Lowers activation energy. Examples: Pt in catalytic converters, enzymes (biological catalysts), Fe in Haber process (NH₃ synthesis). Inhibitor: slows reaction.
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Q76
What is the Doppler effect?
Explanation: Doppler effect: source approaching → observed frequency higher (shorter wavelength). Source moving away → lower frequency (longer wavelength). Applications: radar speed guns, medical ultrasound, redshift in astronomy (universe expanding). Named after Christian Doppler (1842).
Q77
What is centripetal force?
Explanation: Centripetal force: directed toward centre, not a new type of force — can be gravity, tension, normal force, friction, or any combination. F = mv²/r. Centrifugal force: apparent outward force felt in rotating frame (not a real force in inertial frame).
Q78
What is Coulomb's law?
Explanation: Coulomb's law: F = kq₁q₂/r². k = 9×10⁹ N·m²/C². Same form as Newton's gravity but: can be repulsive (same sign charges), electromagnetic force far stronger than gravity. Charge measured in Coulombs (C).
Q79
What is power in physics?
Explanation: Power P = W/t. 1 Watt = 1 Joule/second. Electrical power: P = VI = I²R = V²/R. Mechanical power: P = Fv. Kilowatt-hour (kWh): energy unit on electricity bill (1 kW for 1 hour = 3.6 MJ).
Q80
What is the difference between conductor and insulator?
Explanation: Conductors: metals (Cu, Al, Ag best), graphite, ionic solutions. Semiconductors: Si, Ge — conductivity between. Insulators: rubber, plastic, glass, ceramic, dry air. Semiconductors form basis of all electronics (transistors, chips).
Q81
What is the relationship between force, mass, and acceleration?
Explanation: Newton's Second Law: F_net=ma. Net force = vector sum of all forces. If F_net=0 → acceleration=0 (Newton's 1st law). Example: 2kg object accelerating at 3m/s² requires net force of 6N. Weight = mg (gravitational force on mass m).
Q82
What is gravitational potential energy?
Explanation: Ep=mgh: m=mass (kg), g=9.8 m/s², h=height (m). Reference point is arbitrary. Energy increases as height increases. As object falls, Ep converts to Ek (kinetic). Conservation of mechanical energy: Ep+Ek = constant (if no friction).
Q83
What is the Doppler effect for light?
Explanation: Cosmological redshift: all distant galaxies show redshift → universe is expanding (Hubble 1929). Hubble constant: rate of expansion. Blue-shifted: Andromeda galaxy (approaching). Used in: astronomy, police radar (radio waves), Doppler ultrasound (sound waves, same principle).
Q84
What is the difference between scalar and vector quantities?
Explanation: Scalar: add normally (5kg + 3kg = 8kg). Vectors: must consider direction (3N east + 4N north = 5N at 53° — vector addition, not 7N). Key vectors: displacement (not distance), velocity (not speed), force, acceleration, momentum, weight.
Q85
What is the principle of moments?
Explanation: Moment = F × d (perpendicular distance from pivot). Equilibrium: Σ(clockwise moments) = Σ(anticlockwise moments). Used in: levers, see-saws, engineering structures. Example: 10N force 2m from pivot = 20 N·m moment. Balance: 5N at 4m from other side = 20 N·m.
Q86
What is Faraday's law of electromagnetic induction?
Explanation: Faraday's law: EMF = -ΔΦ/Δt (rate of change of magnetic flux). Lenz's law: induced current opposes the change that causes it (explains negative sign). Applications: generators (mechanical→electrical energy), transformers (change AC voltage), induction cooktops.
Q87
What is a step-up transformer?
Explanation: Transformer equation: Vs/Vp = Ns/Np = Ip/Is. Step-up: Ns > Np → Vs > Vp (current decreases). Step-down: Ns < Np → Vs < Vp (current increases). Power conserved (ideal): P=VI is same on both sides. Used in: power transmission (step-up for efficiency), device chargers (step-down).
Q88
What is nuclear energy?
Explanation: Fission: U-235 + neutron → Ba + Kr + 2-3 neutrons + ~200 MeV energy. Chain reaction. Nuclear power stations use controlled fission. Fusion: H+H→He — powers stars, releases more energy than fission. Controlled fusion (tokamak reactors): still not commercially viable.
Q89
What is projectile motion?
Explanation: Projectile: no air resistance assumed. Horizontal: uniform velocity (no force). Vertical: uniform acceleration (g=9.8 m/s² downward). At maximum height: vertical velocity=0. Range = v²sin(2θ)/g. Maximum range: θ=45°. Time of flight: t=2v_y/g. Independence of horizontal and vertical motion.
Q90
What is the photoelectric equation?
Explanation: Einstein's photoelectric equation: E_k(max) = hf - φ. φ (work function): minimum energy to remove electron. Threshold frequency: f₀ = φ/h. Below f₀: no electrons ejected regardless of intensity. Above f₀: electrons ejected; kinetic energy increases with frequency.
Q91
What is Archimedes' principle?
Explanation: Archimedes' principle: F_buoy = ρ_fluid × V_displaced × g. Object floats if F_buoy ≥ weight. Object floats if density < fluid density (e.g., wood < water). Submarines: adjust buoyancy by flooding/emptying ballast tanks. Ships: displace water equal to their weight.
What is the difference between static and kinetic friction?
Explanation: Static friction: adjusts up to f_s(max)=μ_s × N. Once object moves: kinetic friction = μ_k × N (constant). Always: μ_k < μ_s (easier to keep moving than to start moving). Normal force (N): perpendicular to surface. On inclined plane: N = mg cos θ.
Q94
What is the de Broglie wavelength?
Explanation: de Broglie (1924): wave-particle duality applies to matter. λ=h/mv. For macroscopic objects: wavelength is negligibly small (not observable). For electrons: wavelength is significant → used in electron microscopy. Confirmed by: electron diffraction experiment (Davisson-Germer 1927).
Q95
What is simple harmonic motion (SHM)?
Explanation: SHM: F=-kx (Hooke's law for spring). Period T=2π√(m/k) for spring, T=2π√(L/g) for pendulum. Amplitude: maximum displacement. At equilibrium: max speed, zero PE. At maximum displacement: zero speed, max PE. Energy exchanges between kinetic and potential.
Q96
What is the photoelectric effect's significance?
Explanation: Photoelectric effect: classical wave theory predicted: any frequency with enough intensity would eject electrons. Experiment showed: frequency (not intensity) determines if ejection occurs. Tour only made sense if light is quantised into photons. Established quantum mechanics as a field.
Q97
What is the relationship between electric field and voltage?
Explanation: Electric field E=V/d for uniform field (parallel plates). Direction: from high to low potential. Electric potential energy: Ep=qV. Work done moving charge: W=qV. Field lines: perpendicular to equipotential surfaces, point in direction of decreasing potential.
Q98
What is Snell's law?
Explanation: Snell's law: n = c/v (refractive index). Higher n = slower light. Light bends toward normal when entering denser medium (n increases). Critical angle: angle of incidence in denser medium that gives 90° refraction. Above critical angle: total internal reflection (optical fibres, diamonds). Application: lenses, prisms.
Q99
What is the principle of conservation of charge?
Explanation: Conservation of charge: like conservation of momentum and energy. In circuit: current (charge flow) is conserved. At junction: ΣI_in = ΣI_out (Kirchhoff's current law). Charging by induction: no charge transferred — charge redistribution. Charge quantised: multiples of e=1.6×10⁻¹⁹ C.
Q100
What are isotopes?
Explanation: Isotopes: same Z (atomic number/protons), different A (mass number). Examples: C-12, C-13, C-14 (radioactive). H-1 (protium), H-2 (deuterium), H-3 (tritium). Radioactive isotopes: used in medicine (iodine-131 for thyroid), carbon dating (C-14), power generation (U-235).
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Q101
What is the first law of thermodynamics?
Explanation: First law (conservation of energy): ΔU = Q - W. Q: heat added to system (+), released (-). W: work done BY system (+). Applications: heat engines, refrigerators. Efficiency of engine: W_out/Q_in. Never > 100% (second law: some energy always becomes unusable heat).
Q102
What is diffraction?
Explanation: Diffraction: all waves (light, sound, water). Single slit: wide central bright fringe, narrower side fringes. Double slit (Young's experiment): alternating bright and dark fringes (interference). Applications: X-ray crystallography (determines crystal structure), radio wave diffraction around buildings.
Q103
What is an exothermic vs endothermic reaction?
Explanation: Exothermic: combustion (burning fuel), respiration, neutralisation of acid+base, rusting. Reactants have more energy than products → energy released as heat. Endothermic: photosynthesis, dissolving ammonium nitrate in water. Products have more energy → absorbs heat from surroundings.
Q104
What is a molar mass?
Explanation: Molar mass calculation: add up atomic masses. H₂O: 2(1)+16=18 g/mol. NaCl: 23+35.5=58.5 g/mol. CaCO₃: 40+12+3(16)=100 g/mol. n = m/M. 36g H₂O: 36/18=2 mol. Use in: stoichiometry (mole ratios in balanced equations), concentration calculations.
Q105
What is terminal velocity?
Explanation: Terminal velocity: skydiver: weight (down) = air resistance (up). Initially: weight > resistance → accelerates. As speed increases: resistance increases. At terminal velocity: balanced. Parachute: increases surface area → increases resistance → lower terminal velocity.
Q106
What is electrochemistry and electrolysis?
Explanation: Electrolysis: cathode (-): reduction (cations gain electrons). Anode (+): oxidation (anions lose electrons). Applications: electroplating (chrome on car parts), Hall-Héroult process (aluminium from Al₂O₃), chlor-alkali process (Cl₂ and NaOH from brine). Faraday's law: mass deposited ∝ charge passed.
Q107
What is the photoelectric current?
Explanation: Photoelectric current (I): proportional to light intensity (more photons → more electrons ejected → larger current). Stopping potential (Vs): negative voltage needed to stop all photoelectrons. eVs = E_k(max) = hf - φ. Frequency determines energy per electron; intensity determines number of electrons.
Q108
What is the Heisenberg Uncertainty Principle?
Explanation: Heisenberg (1927): ΔxΔp ≥ ℏ/2. The more precisely position known, the less precisely momentum known, and vice versa. Not a limitation of instruments — fundamental property of quantum systems. Consequence: electrons don't have defined orbits (orbitals: probability distributions instead).
Q109
What is chemical equilibrium constant (K)?
Explanation: For aA + bB ⇌ cC + dD: K=[C]^c[D]^d/[A]^a[B]^b. K>>1: equilibrium favours products. K<<1: equilibrium favours reactants. K only changes with temperature. Concentration, pressure changes shift equilibrium (Le Chatelier) but don't change K.
Q110
What is the electromagnetic force law (F on charge in magnetic field)?
Explanation: Magnetic force on charge: F=qvBsinθ. Maximum when v⊥B (θ=90°). Zero when v∥B. Direction: right-hand rule (or left-hand for negative charge). On current-carrying conductor: F=BILsinθ. Electric motor principle: current in magnetic field → force → rotation.
Q111
What is Le Chatelier's principle?
Explanation: Stresses: concentration (add reactant → shift right), temperature (increase T → shift toward endothermic direction), pressure (increase P → shift toward fewer moles of gas). Catalyst: increases rate of both forward and reverse equally — reaches equilibrium faster but doesn't shift it.
Question 112 of 150
What is Newton's third law?
Explanation: Newton's 3rd Law: If A exerts force on B, B exerts equal and opposite force on A. Pairs always act on different objects. Walking: foot pushes back on ground, ground pushes foot forward.
Question 113 of 150
What is the relationship between wavelength and frequency?
Explanation: Wave equation: v = fλ. v = wave speed (m/s), f = frequency (Hz), λ = wavelength (m). Speed is constant for a medium. Higher frequency → shorter wavelength. Light: f = c/λ.
Question 114 of 150
What is work in physics?
Explanation: Work: W = Fd cosθ. θ is angle between force and displacement. Zero work: force perpendicular to displacement (holding a bag while walking). Negative work: force opposes motion (friction, braking).
Question 115 of 150
What is the conservation of energy?
Explanation: Law of Conservation of Energy: total energy is constant. Potential energy converts to kinetic and vice versa. Friction: kinetic energy → heat. In closed system: ΣE = constant. Real systems: some energy always lost to heat (thermodynamics).
Question 116 of 150
What is electric current?
Explanation: Electric current (I): charge (Q, Coulombs) per time (t, seconds). I = Q/t. In metals: electrons flow (opposite to conventional current direction). Direct current (DC): one direction. Alternating current (AC): direction alternates periodically.
Question 117 of 150
What is the difference between series and parallel circuits?
Explanation: Series: V_total = V₁+V₂+V₃. I = same throughout. R_total = R₁+R₂+R₃. Parallel: I_total = I₁+I₂+I₃. V = same across each branch. 1/R_total = 1/R₁+1/R₂+1/R₃.
Question 118 of 150
What is the electromagnetic force?
Explanation: Four fundamental forces: Gravity (weakest, infinite range), Electromagnetic (light, chemistry, electricity — infinite range), Weak nuclear (radioactive decay), Strong nuclear (holds nucleus together — strongest, very short range).
Question 119 of 150
What is radioactive decay?
Explanation: Radioactive decay types: Alpha (α): helium nucleus emitted, loses 2 protons+2 neutrons. Beta (β): neutron converts to proton, electron emitted. Gamma (γ): high-energy photon emitted, no mass change. Half-life: time for half of nuclei to decay.
Question 120 of 150
What is the mole concept in chemistry?
Explanation: Mole: n = m/M. n = moles, m = mass (g), M = molar mass (g/mol). 1 mol O₂ = 32g = 6.022×10²³ molecules. Avogadro's number: 6.022×10²³. Used to count atoms and molecules.
Question 121 of 150
What is acid-base neutralisation?
Explanation: Neutralisation: acid + base → salt + water. Example: HCl + NaOH → NaCl + H₂O. Strong acid + strong base: pH 7 product. Indicators: change colour at different pH values. Titration: precise neutralisation to determine concentration.
Question 122 of 150
What is momentum?
Explanation: Momentum p = mv. Vector quantity (has direction). Law of Conservation of Momentum: total momentum before collision = total momentum after (in isolated system). Impulse = change in momentum = F×Δt.
Question 123 of 150
What is a chemical bond?
Explanation: Ionic bond: metal gives electrons to non-metal (NaCl). Covalent bond: non-metals share electrons (H₂O, CO₂). Metallic bond: positive metal ions in 'sea' of delocalised electrons (conductivity, malleability). Intermolecular forces: between molecules (H-bonds, Van der Waals).
Question 124 of 150
What is temperature vs heat?
Explanation: Temperature: intensive property (doesn't depend on amount). Heat: extensive property (depends on amount). Specific heat capacity: energy to raise 1kg by 1°C. Q = mcΔT. Thermal equilibrium: heat transfer stops when temperatures equal.
Question 125 of 150
What is the difference between nuclear fission and fusion?
Explanation: Fission: U-235 + neutron → smaller nuclei + 2-3 neutrons + energy. Chain reaction. Used: nuclear reactors, atomic bombs. Fusion: H + H → He + energy. Powers stars. Requires extreme temperatures. Fusion produces far more energy per kg and less waste.
Question 126 of 150
What are the states of matter?
Explanation: States of matter: Solid: particles vibrate in fixed positions. Liquid: particles flow but volume fixed. Gas: particles move freely, fill container. Plasma: extremely hot ionised gas (stars, lightning). Changes of state involve energy (latent heat).
Question 127 of 150
What is the difference between speed and velocity?
Explanation: Speed: total distance / time (scalar). Velocity: displacement / time (vector). An object moving in a circle at constant speed has changing velocity (direction changes). Average vs instantaneous speed/velocity.
Question 128 of 150
What is Charles's Law?
Explanation: Charles's Law: V₁/T₁ = V₂/T₂ (T in Kelvin). At constant pressure: double temperature → double volume. Combined with Boyle's Law and Gay-Lussac's Law → Ideal Gas Law: PV = nRT.
Question 129 of 150
What is Boyle's Law?
Explanation: Boyle's Law: P₁V₁ = P₂V₂ (T constant). Double pressure → half volume. Named after Robert Boyle (1662). Applies to ideal gases. Real gases deviate at high pressure/low temperature.
Question 130 of 150
What is the photoelectric effect?
Explanation: Photoelectric effect (Einstein, 1905): photons with energy E = hf strike metal. If E ≥ work function (φ), electrons emitted. Increasing intensity increases number of electrons but not their energy. Increasing frequency increases electron energy. Proved light is quantised.
Question 131 of 150
What is the half-life of a radioactive substance?
Explanation: Half-life (t½): after 1 t½, N/2 remain. After 2 t½, N/4. After n half-lives: N × (1/2)ⁿ. Examples: Carbon-14 t½ = 5,730 years (radiocarbon dating). Uranium-235 t½ = 704 million years. Used in medicine, archaeology, geology.
Question 132 of 150
What are electromagnetic waves?
Explanation: EM waves: transverse, travel at c = 3×10⁸ m/s in vacuum. All carry energy. No medium required. Visible light: 400-700nm wavelength. Radio: longest wavelength. Gamma: shortest wavelength, highest energy, most penetrating.
Question 133 of 150
What is the ideal gas law?
Explanation: Ideal gas law: PV = nRT. Combines Boyle's, Charles's, and Avogadro's laws. Ideal gas: no intermolecular forces, negligible particle volume. Real gases approximate ideal at low pressure, high temperature.
Question 134 of 150
What is oxidation and reduction (redox)?
Explanation: OIL RIG: Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons). Oxidation number increases: oxidised. Decreases: reduced. Oxidising agent: oxidises others, gets reduced itself. Reducing agent: reduces others, gets oxidised. Fe → Fe³⁺ + 3e⁻ (oxidation).
Question 135 of 150
What is specific heat capacity?
Explanation: Specific heat capacity (c): water c = 4,200 J/kg·K (high — explains oceans moderate climate). Iron c = 450 J/kg·K. Q = mcΔT: Q = heat energy (J), m = mass (kg), c = specific heat, ΔT = temperature change. Higher c → more energy to heat up.
Question 136 of 150
What is a catalyst?
Explanation: Catalyst: not consumed, not appear in balanced equation. Lowers activation energy. Examples: Pt in catalytic converters, enzymes (biological catalysts), Fe in Haber process (NH₃ synthesis). Inhibitor: slows reaction.
Question 137 of 150
What is the Doppler effect?
Explanation: Doppler effect: source approaching → observed frequency higher (shorter wavelength). Source moving away → lower frequency (longer wavelength). Applications: radar speed guns, medical ultrasound, redshift in astronomy (universe expanding). Named after Christian Doppler (1842).
Question 138 of 150
What is centripetal force?
Explanation: Centripetal force: directed toward centre, not a new type of force — can be gravity, tension, normal force, friction, or any combination. F = mv²/r. Centrifugal force: apparent outward force felt in rotating frame (not a real force in inertial frame).
Question 139 of 150
What is Coulomb's law?
Explanation: Coulomb's law: F = kq₁q₂/r². k = 9×10⁹ N·m²/C². Same form as Newton's gravity but: can be repulsive (same sign charges), electromagnetic force far stronger than gravity. Charge measured in Coulombs (C).
Question 140 of 150
What is power in physics?
Explanation: Power P = W/t. 1 Watt = 1 Joule/second. Electrical power: P = VI = I²R = V²/R. Mechanical power: P = Fv. Kilowatt-hour (kWh): energy unit on electricity bill (1 kW for 1 hour = 3.6 MJ).
Question 141 of 150
What is the difference between conductor and insulator?
Explanation: Conductors: metals (Cu, Al, Ag best), graphite, ionic solutions. Semiconductors: Si, Ge — conductivity between. Insulators: rubber, plastic, glass, ceramic, dry air. Semiconductors form basis of all electronics (transistors, chips).
Question 142 of 150
What is the relationship between force, mass, and acceleration?
Explanation: Newton's Second Law: F_net=ma. Net force = vector sum of all forces. If F_net=0 → acceleration=0 (Newton's 1st law). Example: 2kg object accelerating at 3m/s² requires net force of 6N. Weight = mg (gravitational force on mass m).
Question 143 of 150
What is gravitational potential energy?
Explanation: Ep=mgh: m=mass (kg), g=9.8 m/s², h=height (m). Reference point is arbitrary. Energy increases as height increases. As object falls, Ep converts to Ek (kinetic). Conservation of mechanical energy: Ep+Ek = constant (if no friction).
Question 144 of 150
What is the Doppler effect for light?
Explanation: Cosmological redshift: all distant galaxies show redshift → universe is expanding (Hubble 1929). Hubble constant: rate of expansion. Blue-shifted: Andromeda galaxy (approaching). Used in: astronomy, police radar (radio waves), Doppler ultrasound (sound waves, same principle).
Question 145 of 150
What is the difference between scalar and vector quantities?
Explanation: Scalar: add normally (5kg + 3kg = 8kg). Vectors: must consider direction (3N east + 4N north = 5N at 53° — vector addition, not 7N). Key vectors: displacement (not distance), velocity (not speed), force, acceleration, momentum, weight.
Question 146 of 150
What is the principle of moments?
Explanation: Moment = F × d (perpendicular distance from pivot). Equilibrium: Σ(clockwise moments) = Σ(anticlockwise moments). Used in: levers, see-saws, engineering structures. Example: 10N force 2m from pivot = 20 N·m moment. Balance: 5N at 4m from other side = 20 N·m.
Question 147 of 150
What is Faraday's law of electromagnetic induction?
Explanation: Faraday's law: EMF = -ΔΦ/Δt (rate of change of magnetic flux). Lenz's law: induced current opposes the change that causes it (explains negative sign). Applications: generators (mechanical→electrical energy), transformers (change AC voltage), induction cooktops.
Question 148 of 150
What is a step-up transformer?
Explanation: Transformer equation: Vs/Vp = Ns/Np = Ip/Is. Step-up: Ns > Np → Vs > Vp (current decreases). Step-down: Ns < Np → Vs < Vp (current increases). Power conserved (ideal): P=VI is same on both sides. Used in: power transmission (step-up for efficiency), device chargers (step-down).
Question 149 of 150
What is nuclear energy?
Explanation: Fission: U-235 + neutron → Ba + Kr + 2-3 neutrons + ~200 MeV energy. Chain reaction. Nuclear power stations use controlled fission. Fusion: H+H→He — powers stars, releases more energy than fission. Controlled fusion (tokamak reactors): still not commercially viable.
Question 150 of 150
What is projectile motion?
Explanation: Projectile: no air resistance assumed. Horizontal: uniform velocity (no force). Vertical: uniform acceleration (g=9.8 m/s² downward). At maximum height: vertical velocity=0. Range = v²sin(2θ)/g. Maximum range: θ=45°. Time of flight: t=2v_y/g. Independence of horizontal and vertical motion.
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Newton's second law states that the net force acting on an object equals its mass multiplied by acceleration: Fnet = ma. Force is measured in Newtons (N), mass in kilograms (kg), and acceleration in m/s². A larger net force produces greater acceleration; a larger mass requires more force for the same acceleration.
Work = Force × displacement × cos θ (measured in Joules). Energy is the capacity to do work (also Joules). Power = Work ÷ Time = Energy ÷ Time (measured in Watts). The work-energy theorem states that the net work done on an object equals its change in kinetic energy: Wnet = ΔEk.
In an isolated system (no external net force), the total momentum before a collision equals the total momentum after: Σp_before = Σp_after. Elastic collisions conserve both momentum and kinetic energy. Inelastic collisions conserve momentum but not kinetic energy (some is converted to heat, sound, or deformation).
Ohm's Law states that the potential difference (voltage) across a conductor is directly proportional to the current flowing through it, provided temperature remains constant: V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). Power: P = VI = I²R = V²/R.
In a series circuit, components are connected end-to-end. Total resistance = R₁ + R₂ + R₃ (increases). Current is the same throughout; voltage divides. In a parallel circuit, components are connected across the same two points. 1/Rtotal = 1/R₁ + 1/R₂ (total resistance decreases). Voltage is the same across each branch; current divides.
The photoelectric effect is the emission of electrons from a metal surface when light of sufficient frequency (above the threshold frequency) shines on it. Einstein explained tour by proposing that light consists of photons, each with energy E = hf (h = Planck's constant, f = frequency). Tour proved the quantum nature of light and earned Einstein the Nobel Prize.
Le Chatelier's principle states that if a stress is applied to a system at equilibrium, the system will shift in the direction that partially relieves that stress. Stresses include: concentration change (system shifts to reduce concentration of added substance), temperature change (increase temperature shifts equilibrium towards endothermic direction), and pressure change (increase pressure shifts towards fewer moles of gas).
An acid is a proton donor (Brønsted-Lowry definition) or an electron pair acceptor (Lewis). A base is a proton acceptor or electron pair donor. Strong acids fully dissociate in water (HCl, H₂SO₄, HNO₃). Weak acids partially dissociate (CH₃COOH). pH = −log[H₃O⁺]. Neutral: pH=7. Acid: pH<7. Base: pH>7.