9702/21/O/N/25 Q1–Q6 Full Paper 21 Solved | A Level Physics | Cambridge 9702

9702 paper 21 | October November 2025 | Cambridge A Level Physics | full paper solution | Q1 rocket motion | Q2 pressure upthrust viscosity | Q3 Young modulus wire spring | Q4 diffraction grating polarisation | Q6 tritium quarks | Kirchhoff thermistor | past paper walkthrough | Manim animation | pionspisqrt Full animated solutions for Cambridge International A Level Physics 9702 — Paper 21, October/November 2025. All six questions (Q1–Q6), no intro hook — straight into the worked solutions. 📘 PAST PAPER (shown on screen) Tag: 9702/21 O/N/25 Cambridge International A Level Physics (9702) Paper 21 | October/November 2025 | Questions 1–6 🎬 ABOUT THIS VIDEO • Manim blackboard animations with step-by-step working • Azure Neural TTS (Sonia, British English), −5% rate, synced narration • Licensed Azure Speech API production • 4K render (2160p60) 📚 QUESTIONS COVERED Q1 — Rocket motion & energy (acceleration, v–t graph, PE, KE, power) Q2 — Pressure, upthrust & viscosity (terminal speed, Stokes drag) Q3 — Young modulus & the wire-spring (ρ, R, k, copper wire) Q4 — Diffraction grating & polarisation (d sin θ = nλ, Malus's law) Q5 — Kirchhoff & the thermistor circuit (KCL, NTC, parallel combination) Q6 — Tritium: structure, decay & quarks (β⁻ decay, quark counting) ⏱ CHAPTERS — MAIN (Q starts) 0:00 Q1 — Rocket motion & energy 1:41 Q2 — Pressure, upthrust & viscosity 3:15 Q3 — Young modulus & the wire-spring 4:44 Q4 — Diffraction grating & polarisation 6:50 Q5 — Kirchhoff & the thermistor circuit 8:58 Q6 — Tritium: structure, decay & quarks ⏱ CHAPTERS — FULL (all parts) 0:00 Q1 — Rocket motion & energy 0:10 Q1 Part (a) — Define acceleration 0:17 Q1 Part (b) — v–t graph setup 0:26 Q1 Part (b)(i) — Gradient → a = 16 m s⁻² 0:38 Q1 Part (b)(ii) — Area → s = 3.2 km 0:50 Q1 Tip — v–t graph 0:56 Q1 Part (c) — Energy setup 1:07 Q1 Part (c)(i) — Gain in GPE 1:16 Q1 Part (c)(ii) — Gain in KE 1:25 Q1 Part (c)(iii) — Average power 1:35 Q1 Tip — Total energy for power 1:41 Q2 — Pressure, upthrust & viscosity 1:53 Q2 Part (a) — Pressure & upthrust 2:06 Q2 Part (b)(i) — Forces on falling ball 2:11 Q2 Weight W 2:15 Q2 Upthrust U 2:18 Q2 Drag D = 6πηrv 2:24 Q2 Tip — Drag opposes motion 2:27 Q2 Part (b)(ii) — Base units of η 2:36 Q2 Part (c) — Terminal speed setup 2:47 Q2 Part (c)(i) — Upthrust U = ρgV 2:59 Q2 Part (c)(ii) — Terminal speed 3:10 Q2 Tip — Forces balance at terminal speed 3:15 Q3 — Young modulus & the wire-spring 3:27 Q3 Parts (a)(b) — E, stress, strain, R = ρL/A 3:38 Q3 Part (b)(ii) — k₀ = EA/L 3:51 Q3 Part (c) — R vs F and k vs F graphs 4:03 Q3 Part (d) — Copper wire data 4:17 Q3 Part (d)(i) — Length L 4:27 Q3 Part (d)(ii) — Spring constant k 4:37 Q3 Tip — Same area A in R and k 4:44 Q4 — Diffraction grating & polarisation 4:56 Q4 Part (a) — Define diffraction 5:08 Q4 Part (b) — Grating setup (λ, d) 5:20 Q4 Central order n = 0 5:23 Q4 1st order θ₁ = 6.2° 5:31 Q4 2nd order θ₂ = 12.5° 5:38 Q4 Tip — Higher orders dimmer 5:42 Q4 Grating equation d sin θ = nλ 5:51 Q4 Part (b)(i) — First order angle 6:03 Q4 Part (b)(ii) — Second order angle 6:14 Q4 Unit conversion nm → m 6:25 Q4 Part (b)(iii) — Intensity pattern 6:36 Q4 Part (c) — Malus's law / polariser at 45° 6:50 Q5 — Kirchhoff & the thermistor circuit 7:01 Q5 Part (a) — Kirchhoff's first law 7:14 Q5 Circuit build 7:23 Q5 Current path 7:32 Q5 Junction — I_cell = I_R + I_T 7:43 Q5 Part (b)(i) — NTC thermistor 7:50 Q5 Part (b)(ii) — Why I_R falls when T rises 8:13 Q5 Part (c) — Full calculation (I_T, R_T) 8:58 Q6 — Tritium: structure, decay & quarks 9:11 Q6 Part (a)(i) — Protons, neutrons, electrons 9:23 Q6 Part (a)(ii) — Atom model 9:31 Q6 Part (b)(i) — β⁻ decay equation 9:41 Q6 Decay balance — nucleon & proton numbers 9:52 Q6 Part (b)(ii) — X = electron antineutrino 9:57 Q6 Tip — Balance top and bottom numbers 10:01 Q6 Part (c) — Quark count (4u, 5d) 10:16 Q6 Tip — Count quarks across nucleons 🔊 CREDITS Manim Community | Azure en-GB-SoniaNeural | pionspisqrt.com 📌 Education only. Not affiliated with Cambridge Assessment International Education. #9702 #Cambridge9702 #ALevelPhysics #PastPaper #Paper21 #ON2025 #9702Paper21 #RocketMotion #YoungModulus #DiffractionGrating #Thermistor #Kirchhoff #Tritium #Quarks #Manim #AzureTTS #ExamSolutions #LearnPhysics #PhysicsAnimation #FullPaper #Q1Q6