VPhO Problems and Solutions
Vietnam's national olympiad for upper-secondary students (Kỳ thi chọn học sinh giỏi quốc gia THPT), set by the Ministry of Education and Training: two written papers on consecutive days, with a practical day in some years. Each edition is named for the school year it closes; the best scorers go on to the team selection test.
All Mechanics Electromagnetism Thermodynamics Waves & Optics Modern & Quantum Relativity Astrophysics
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Kinematics Dynamics Rigid body Fluids Gravitation Statics Electrostatics Circuits Magnetostatics Induction Em waves Heat transfer Gas laws Entropy Kinetic theory Phase transitions Statistical mechanics Oscillations Wave propagation Sound Interference Geometrical optics Atomic Nuclear Particle Solid state Quantum mechanics Special relativity General relativity Stellar Orbital mechanics
2026
Vietnam
1 Traditional bow versus compound pulley bow* not published 2 Bimetallic thermal relay in a kettle* not published 3 Supercapacitor electric double layer* not published 4 Two-plate interferometer measurements* not published 5 Controlled D-T fusion plasma* not published 6 Steel coil safety on a braking truck* not published 7 Phase changes of water and a steam cycle* not published 8 Silicon p-n junction depletion layer* not published 9 Coincidence rangefinder optics* not published 10 Fan capacitor and glass thermal expansion experiments* not published
2025
Vietnam
1 Particle-ejecting device on a line and in a ring* not published 2 Pressure melting of an ice-water mixture* not published 3 Spherical-shell homopolar motor* not published 4 Thin-film colours of feathers and multilayer mirrors* not published 5 Bohr model of hydrogen, deuterium and helium* not published 6 T-shaped pendulum with a released pivot pin* not published 7 Pirani gauge heat conduction* not published 8 Defibrillator capacitor discharge* not published 9 Thick lenses and a periscope telescope* not published 10 Heat capacity of air and of a metal* not published
2024
Vietnam
1 Ore grains on a vibrating inclined plate* not published 2 Capillary rise and merging water drops* not published 3 Polarizable sphere on a charged ring's axis* not published 4 Ray paths in a Luneburg lens* not published 5 Uranium-lead dating of meteorites* not published 6 Toppling half-cylinder on a smooth floor* not published 7 Solar radiation and Earth's surface temperature* not published 8 Charged rotating cylindrical shell fields* not published 9 Interference from two tilted glass plates and a lens* not published 10 Oscilloscope phase method for capacitance* not published
2023
Vietnam
1 Spacecraft transfer orbits around the Sun* not published 2 Joule-cycle air conditioner cooling a room* not published 3 Ring rotating in a uniform magnetic field* not published 4 Split-lens interference fringes* not published 5 Polonium alphas on beryllium and the neutron* not published 6 Band brake on a rotating cylinder* not published 7 LiF crystal lattice energy and expansion* not published 8 Charge moving between two parallel currents* not published 9 Telescope with a glass parallelogram prism* not published 10 Magnet in Helmholtz coils and tungsten filament heat capacity* not published
2022
Vietnam
1 Rod sliding on a circular arc support* not published 2 Gas cycle with three isotherms* not published 3 Charged disc bouncing between capacitor plates* not published 4 Mirror-box ray paths and the Michelson aether test* not published 5 Pion decay muons and a relativistic electron in a field* not published 6 Hollow cylinder rolling with an attached mass* not published 7 Gas centrifuge isotope enrichment* not published 8 Current loop swinging in a magnetic field* not published 9 Beam-narrowing optics and radiation pressure on a mirror* not published 10 NTC band gap and three-voltmeter fan power* not published
2021
Vietnam
1 Projectile and toy car on incline* not published 2 Adiabatic atmosphere height and cloud base* not published 3 Switched circuit with diodes and LC* not published 4 Interference from a biprism* not published 5 Compton scattering energy and angle limits* not published 6 Plate pendulum and disc in cylinder* not published 7 Spring-mounted disc damped by rarefied gas* not published 8 Charged particle in crossed fields* not published 9 Ray in a piecewise graded-index sphere* not published 10 RLC black box and core permeability* not published Experiment 1 problem LED threshold voltages and wavelengths* Problem 11 Experiment LED threshold voltages and wavelengths* Problem VPhO 2021 Experiment problem 11, LED threshold voltages and wavelengths
2020
Vietnam
1 Crank and connecting rod kinematics* not published 2 Ideal gas five-point cycle efficiency* not published 3 Rutherford scattering and liquid-drop nucleus* not published 4 Sighting telescope with a two-lens eyepiece* not published 5 Gravitational redshift from a classical argument* not published 6 Truck suspension when accelerating and cornering* not published 7 Evaporation of water from a cup* not published 8 Square loops entering a varying field* not published 9 White-light double slit, moving source* not published 10 Spring constant from a current-carrying spring* not published
2019
Vietnam
1 Two masses joined by a string* not published 2 Piston dropped on insulated gas* not published 3 Coulomb explosion of a charged cloud* not published 4 Electrowetting liquid lens in phones* not published 5 Laser radiation force on a prism* not published 6 Gas strut opening a boot lid* not published 7 Dewar flask and gas thermal conductivity* not published 8 Two-coil RL circuit transients* not published 9 Hydrogen spectrum and Bohr energy levels* not published 10 Fluxgate magnetometer operation* not published
2018
Vietnam
1 Fastest running route across a lawn* not published 2 Hot-air balloon lift and heating* not published 3 Electron motion in a cylindrical magnetron* not published 4 Door peephole made of two lenses* not published 5 Two-step radioactive decay chain* not published 6 Four-disc spinner rotating about a pivot* not published 7 Gas flow through a leaky calorimeter* not published 8 Aircraft landing guidance by antenna interference* not published 9 Light rays in a graded-index sphere* not published 10 Bridge resistance and ballistic galvanometer field* not published 11 Experiment Resistor-diode black box from I-V curve* Problem Solution VPhO 2018 Experiment problem 11, Resistor-diode black box from I-V curve
2017
Vietnam
1 Sphere rolling in a V-groove* not published 2 Clausius-Clapeyron and humidity in the atmosphere* not published 3 Debye screening in an ion mixture* not published 4 Graded-index flat lens in motion* not published 5 Compton scattering in two frames* not published 6 Bead on a rotating vertical hoop* not published 7 Adiabatic and free gas expansion* not published 8 Two sliding rods on magnetic rails* not published 9 Two-lens system with rotatable lens* not published 10 Sealed tube bore by torsional oscillation* not published 11 Experiment Mechanical black box with hidden ball* Problem Solution VPhO 2017 Experiment problem 11, Mechanical black box with hidden ball
2016
Vietnam
1 Mass on two springs over pulley* not published 2 Monatomic gas parallelogram cycle* not published 3 Double slit with a filament source* not published 4 Magnetism as relativistic effect of charges* not published 5 Lamp filament length and lens index* not published 6 Foucault pendulum and the Coriolis force* not published 7 Soap film oscillation and bubble blowing* not published 8 Inductor boost converter for vehicles* not published 9 Imaging by a spherical refracting surface* not published 10 Compton electron striking a hydrogen atom* not published Experiment 1 problem Photodiode I-V curve and electron charge* Problem Solution 11 Experiment Photodiode I-V curve and electron charge* Problem Solution VPhO 2016 Experiment problem 11, Photodiode I-V curve and electron charge
2015
Vietnam
1 Homopolar motor and eddy-current brake* not published 2 Reversible air conditioner and heat pump* not published 3 Capacitor with a position-dependent dielectric* not published 4 Glass reflection losses and anti-reflection coating* not published 5 Tube shear modulus by torsional oscillation* not published 6 Sphere rolling on sphere, stacked drop* not published 7 Isothermal compression of humid air* not published 8 Thomson plum-pudding model of hydrogen* not published 9 Surveying telescope with a two-lens eyepiece* not published 10 Relativistic charge in a magnetic field* not published
2014
Vietnam
1 Double cone rolling on sliding supports* not published 2 Real gas expansion and cycle efficiency* not published 3 Particle drifting between two magnetic fields* not published 4 Bohr model of hydrogen-like ions* not published 5 X-ray cutoff and inverse Compton scattering* not published 6 Tethered block on a rough incline* not published 7 Isothermal expansion of vapour and air* not published 8 Rotating magnetic field of three-phase coils* not published 9 Ray in a graded-index hollow cylinder* not published 10 Bar magnet's magnetic moment from oscillations* not published 11 Experiment Prism refractive index by ray tracing* Problem Solution VPhO 2014 Experiment problem 11, Prism refractive index by ray tracing
2013
Vietnam
1 Sphere impact on a wedge* not published 2 Gas cycle with quadratic pressure law* not published 3 Solenoid current rise and oscillating inductance* not published 4 Interference from a thin optical wedge* not published 5 Dielectric permittivity and breakdown field measurement* not published 6 Bead on a rotating power-law wire* not published 7 Heat capacity difference for real gases* not published 8 Zero-resistance loop in nonuniform field* not published 9 Folded refracting telescope with two mirrors* not published 10 Liquid viscosity with a rotating-cylinder viscometer* not published 11 Experiment Black-box component from I-V curve* Problem Solution VPhO 2013 Experiment problem 11, Black-box component from I-V curve
2012
Vietnam
1 Sphere rolling on a sliding wedge* not published 2 Diatomic gas cycle with two isotherms* not published 3 Charged particle in axisymmetric magnetic field* not published 4 Apparent depth in a graded liquid* not published 5 Sound speed from accelerating-car Doppler shift* not published 6 Rocking hoop with an attached bead* not published 7 Buoyancy in stratified and humid air* not published 8 RL circuit transient after switch opening* not published 9 Fixed-focus camera depth of field* not published 10 Field mill for Earth's electric field* not published
2011
Vietnam
1 Cylinder rolling inside a quarter-cylinder trough* not published 2 Gas in a decelerating cylinder* not published 3 Dielectric withdrawn from a cylindrical capacitor* not published 4 Point source at meniscus lens centre* not published 5 Classical radiative collapse of hydrogen* not published 6 Physical pendulum reaction and percussion centre* not published 7 RLC circuit with cos-squared voltage* not published 8 Two-lens system with a graded-index plate* not published 9 Argon-hydrogen adiabat and solar cell* not published
2010
Vietnam
1 Rod on two strings, one cut* not published 2 Ice sphere melting in a lake* not published 3 Superconducting ring entering a magnetic field* not published 4 White light dispersion in a prism* not published 5 Raindrop growing while falling through cloud* not published 6 Fresnel drag coefficient from relativity* not published 7 Nitrogen molecule size from capillary flow* not published
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The papers and solutions were shared by Lê Xuân Bảo, physics teacher at Phan Boi Chau High School for the Gifted, Vinh. Papers are in Vietnamese.
Titles marked * are ours, for problems the exam left unnamed.
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