Physics Tells
Patterns for recognizing what a Physics question is really asking — the clue that identifies the answer, the trap it's built to catch, and the shortcut that answers it fast.
Physics questions are spread evenly — no subtopic is more than one question in seven. Waves, mechanics, electricity and magnetism, and nuclear physics together make up half; skip none of the ten.
| Subtopic | Share · highest-yield topics |
|---|---|
| Waves, Sound & Optics | 14% · standing waves and harmonics, decibels, lenses and mirrors, refraction |
| Mechanics, Forces & Motion | 14% · free fall and projectiles, friction, net force and equilibrium |
| Electricity & Magnetism | 13% · Coulomb's law, magnetic force on moving charges, induction |
| Nuclear & Particle Physics | 12% · decay types, quarks and force carriers, relativity |
| Electric Circuits & Current | 10% · series vs. parallel, capacitors, power, semiconductors |
| Circular Motion, Rotation & Gravitation | 9% · orbits, angular momentum, moment of inertia |
| Work, Energy, Power & Momentum | 8% · collisions, kinetic energy, power |
| Harmonic Motion & Fluids | 8% · pendulum and spring periods, buoyancy, Bernoulli |
| Thermodynamics | 7% · Carnot efficiency, gas processes, heat and phase change |
| Quantum Mechanics & Atomic Physics | 7% · photoelectric effect, hydrogen energy levels, spin and Pauli |
These tells come from how a question is built, before you even reach its content.
"By what factor is … multiplied?"
One of the most common Physics question types, and the answer never needs the actual numbers. Write the proportionality (F ∝ 1/r2), plug in only the changes, and multiply. Ignore every quantity the formula doesn't contain. "Unchanged" is a real answer — say 1, not "it is unchanged."
"Which is NOT true / EXCEPT / LEAST"
About one multiple-choice question in fourteen flips the logic: three choices are true and the false one is the answer. Rephrase it as "find the one that isn't true." The false choice is usually a true law with one word swapped — static for kinetic, W boson for gluon, the center of an ellipse for its focus.
"Identify all of the following…"
Usually a bonus, and common in Physics. Judge each item on its own. If you're forced to guess: two items is the most common answer, "all" comes up about one time in five, and "none" is rare.
"Rank / order the following"
Rare and almost always a bonus: friction coefficients, the speed of sound in different materials, radiation penetrating power, moments of inertia. Place the two extremes first, fill in the middle, then check the direction asked for.
Give exactly the form asked for
More than half of Physics short-answer questions are numbers, and they are graded on form:
- Velocity carries a sign — a ball tossed up at 20 m/s, its velocity at 2.5 s → "−5" or "5 down," not "5." So does a focal length "with the proper sign": −6 for a convex mirror.
- An amount doesn't — "how much heat is discarded" → 1200 J, not −1200.
- The full name — "Gauss's law for magnetism," "Kepler's second law," "Faraday cage" (not "shielding") — the shorter or vaguer version is marked wrong.
- Units — "in proper SI units" means the unit is part of the answer: "784 newtons."
- Rounding — "to two significant figures" means 1300, not 1334.
Physics questions hinge on one word that picks which quantity, which moment, or which object is meant. When you hear one, ask "what would the answer be without this word?" That answer is the trap.
Which quantity, which moment?
- "Velocity" vs. "speed" — velocity counts only where you end up. "The magnitude of your average velocity for one lap of a 70-meter-radius track" → 0; the distance-over-time speed is the trap.
- "At its highest point" — the velocity is zero, the acceleration is not. A ball thrown straight up, at the top → velocity zero, acceleration still g, downward; zero acceleration is the trap.
- "Terminal velocity" — drag equals weight, so the net force is zero. "The acceleration of a falling body after it reaches terminal velocity" → 0; 9.8 is the trap.
- "Apparent weight" or a scale reading — it reveals the acceleration, not the direction of motion. A scale reading drops from 200 to 190 N → accelerating downward: speeding up going down or slowing down going up; assuming it must be moving down is the trap.
- "Floating" — the buoyant force equals the full weight, however much is submerged. "One-third submerged: ratio of buoyant force to gravity" → 1; 1/3 is the trap.
Which change, which object?
- "Passes from one medium to another" — speed and wavelength change; the frequency, set by the source, never does. "Which of period, wavelength, and speed change" → 2 and 3; including the period is the trap.
- "Perfectly inelastic" — momentum is conserved in every collision; kinetic energy only in elastic ones. "Which quantity is NOT conserved" → kinetic energy.
- "First overtone" — the first harmonic above the fundamental. "The first overtone of a guitar string is what harmonic?" → second; "first" is the trap.
- "Uniform" vs. "non-uniform" field — a uniform electric field only twists a dipole; a net force needs a non-uniform one. Of uniform E, non-uniform E, and uniform B → non-uniform E only.
- "Stationary" vs. "moving" charge — a magnetic field pushes only moving charges. "Which feel a magnetic force: a stationary charge, a moving charge, a current-carrying wire" → the last two.
Many terms come in easily confused pairs. When the answer is one term in a pair, the other is often a wrong choice. Learn each pair with the one difference that tells them apart.
| Pair | What tells them apart |
|---|---|
| Mass vs. weight | Amount of matter, in kg, same everywhere vs. the force of gravity on it, in newtons (W = mg) |
| Static vs. kinetic friction | Holds a resting object vs. slows a sliding one; the static coefficient is larger, so starting a push is harder than keeping it going |
| Centripetal vs. centrifugal | The real inward force that keeps a circle going vs. the outward push felt only from inside the rotating frame |
| Series vs. parallel: resistors | Series resistances add (total is larger) vs. parallel total is smaller than the smallest one |
| Series vs. parallel: capacitors | The reverse of resistors: parallel capacitances add; series total is smaller than the smallest |
| Transverse vs. longitudinal wave | Vibrates across the direction of travel (light, string waves, S waves) vs. along it in compressions (sound, P waves); only transverse waves can be polarized |
| Node vs. antinode | Point that never moves vs. point of largest motion |
| Real vs. virtual image | Light actually meets there, inverted, can land on a screen vs. only appears to come from there, upright |
| Fission vs. fusion | A heavy nucleus splits (uranium, reactors) vs. light nuclei join (hydrogen to helium, the Sun) |
| Fermion vs. boson | Half-integer spin, obeys Pauli exclusion (quarks, electrons, protons) vs. integer spin (photons, gluons, W, Z, Higgs) |
| n-type vs. p-type semiconductor | Doped with a Group 15 element (P, As, Sb) for extra electrons vs. a Group 13 element (B, Al, Ga) for "holes" |
| Paramagnetic vs. diamagnetic | Unpaired electrons, weakly pulled into a field vs. all paired, weakly pushed out; ferromagnetic (iron) is strongly pulled |
| Special vs. general relativity | Constant speed of light, time dilation, E = mc2 vs. gravity as curved spacetime (Mercury's orbit, light bending) |
Many physics terms are built from Greek or Latin parts that say what they mean. Read the parts and an unfamiliar process or particle usually sorts itself.
| Word part | What it tells you |
|---|---|
| iso- (same) + -thermal / -baric / -choric; isentropic | Constant temperature / pressure / volume; constant entropy |
| adiabatic (“not passing through”) | No heat enters or leaves |
| hadron (bulky), baryon (heavy), meson (middle), lepton (light) | Hadrons are made of quarks: baryons have three (proton, neutron), mesons a quark and an antiquark; leptons (electron, muon, tau, neutrinos) aren't made of quarks |
| anti-, positron | Same mass, opposite charge; the positron is the anti-electron |
| dia- (against), para- (alongside), ferro- (iron) | Magnetism that opposes the field, follows it weakly, or follows it strongly |
| nano-, micro-, milli-, kilo-, mega-, giga- | 10−9, 10−6, 10−3, 103, 106, 109 — convert before you calculate |
Many questions describe a situation instead of naming the principle. 1) Name the principle the situation is built on — a conservation law, a force balance, a proportionality. 2) Decide what it says is constant and what changes. 3) Before answering, name the look-alike the question is built to catch and confirm your answer beats it.
Forces and motion
Before any calculation, ask whether the velocity is changing. If it isn't — at rest, constant velocity, terminal speed — the forces balance and the question is usually arithmetic.
| Clue in the question | Answer |
|---|---|
| Pulled at constant velocity; find the friction coefficient | Pull = friction, so μ = F / (mg): 60 N on 20 kg → 0.3 |
| Dropped vs. thrown horizontally from the same height | Land at the same time — horizontal speed doesn't affect the fall |
| Projectile in flight | Horizontal velocity constant; acceleration is g downward at every point |
| Constant speed in a circle; is it in equilibrium? | No — the direction changes, so there's a net inward force |
Energy, momentum, and rotation
Name the conserved quantity first. Momentum survives every collision and explosion; angular momentum survives any change with no outside twist; kinetic energy survives only elastic collisions.
| Clue in the question | Answer |
|---|---|
| Skater pulls arms in / Kepler's second law / planet faster near the star | Conservation of angular momentum |
| Cargo dropped into a rolling truck | Momentum conserved: same momentum, more mass, slower |
| Race down a ramp: sphere, cylinder, hoop | Smallest moment of inertia for its mass wins: solid sphere first, hoop last |
| Energy to go 0 → 10 vs. 10 → 20 m/s | KE ∝ v2: 100 vs. 300 units, so 3 times as much |
Orbits and gravity
Every orbit question runs on one balance: gravity supplies the centripetal force. Farther out means weaker pull, so everything slows down.
| Clue in the question | Answer |
|---|---|
| Farther orbit | Slower speed (v ∝ 1/√r: 4× as far, half the speed), longer period |
| Escape speed from orbit | √2 × orbital speed: 10 km/s orbit → 14 km/s |
| Planet in an elliptical orbit; what's conserved? | Angular momentum and total energy; speed and kinetic energy are lowest at the far point |
| The Sun shrinks but keeps its mass | Orbits don't change — only mass and distance matter |
Oscillations and fluids
Ask what the period depends on before computing it — the trap is usually a variable that doesn't appear in the formula at all.
| Clue in the question | Answer |
|---|---|
| Pendulum period | T ∝ √L; mass doesn't matter; 4× the length doubles the period |
| Spring period | T ∝ √(m/k); gravity doesn't matter; halve the mass → period ÷ √2 |
| Fraction submerged when floating | = object density ÷ fluid density: 800 in 1000 → 80% under, 20% above |
| Fluid speeds up in a narrow pipe | A1v1 = A2v2, and faster flow means lower pressure (Bernoulli) |
Thermodynamics
Translate the process name into which quantity is zero, then the first law (ΔU = Q − W, change in internal energy = heat in minus work done) gives the rest.
| Clue in the question | Answer |
|---|---|
| Isothermal / adiabatic / isochoric | ΔU = 0 (Q = W) / Q = 0 / W = 0 |
| Carnot efficiency | 1 − Tcold/Thot in kelvin: 527°C and 127°C → 800 K and 400 K → 50%; using Celsius is the trap |
| Heat added to ice water | Stays at 0°C until all the ice melts |
| Statement of the second law | Heat flows only hot to cold; no engine beats Carnot; entropy of the universe never decreases |
Electric and magnetic fields
Picture the directions before answering. A magnetic force is always perpendicular to both the velocity and the field, and that one fact settles most of these questions.
| Clue in the question | Answer |
|---|---|
| Charged particle in a magnetic field | Force ⊥ velocity: does no work, speed unchanged, moves in a circle; period independent of speed |
| Direction of field around a wire or force on a charge | Right-hand rule: thumb along current, fingers curl with B; flip the result for a negative charge |
| Flux through a closed surface around a charge | Depends only on the charge enclosed (Gauss): change the surface's size → factor 1 |
| Changing magnetic field through a loop | Induced current opposes the change (Lenz's law): eddy currents, magnetic braking, metal detectors |
Circuits
Identify what stays the same across each piece: current in series, voltage in parallel. Then every bulb and resistor question answers itself.
| Clue in the question | Answer |
|---|---|
| One of two parallel bulbs burns out | The other is unchanged (factor 1) — it keeps the full voltage |
| Two bulbs in series vs. one alone | Dimmer — double resistance, half the current |
| Wire radius doubled | R ∝ length/area → resistance × 1/4 |
| Most stored energy from batteries and capacitors | Batteries in series (voltages add), capacitors in parallel (capacitances add) |
Waves and sound
Classify the setup first — string, open pipe, closed pipe, moving source — and the pattern gives the answer without a formula.
| Clue in the question | Answer |
|---|---|
| String, or pipe open at both ends / pipe closed at one end | All harmonics (f, 2f, 3f…) / odd harmonics only (f, 3f, 5f…) |
| Source moving toward you | Higher pitch (Doppler); away → lower |
| Tuning two strings by beats | Beat frequency = difference of the two; in tune at 0 |
| Supersonic plane overhead | The sonic boom arrives after the plane has passed |
Light and optics
Sort the optic into converging (convex lens, concave mirror) or diverging (concave lens, convex mirror) before anything else. A diverging one gives the same answer every time.
| Clue in the question | Answer |
|---|---|
| Convex mirror or diverging lens | Always virtual, upright, smaller; negative focal length |
| Concave mirror, object beyond the focal point | Real and inverted; focal length = R/2 (radius 54 cm → 27 cm) |
| Total internal reflection | Only going from higher to lower index (glass to air), beyond the critical angle: sin θc = n2/n1 |
| Why the sky is blue | Rayleigh scattering, ∝ 1/λ4, so blue scatters most |
Quantum and atomic
Most questions here ask which picture of light a result supports. Sort each experiment into "light as particles" or "light as waves" first.
| Clue in the question | Answer |
|---|---|
| Photoelectric effect: brighter light / higher frequency | More electrons, same energy / faster electrons; below the work function, none at all |
| Evidence for particles / for waves | Photoelectric effect, Compton scattering / diffraction, double slit; Davisson–Germer showed electrons act as waves |
| Hydrogen spectral series | Ending at n = 1 / 2 / 3: Lyman (UV) / Balmer (visible) / Paschen (infrared) |
| Two electrons in one orbital need opposite spins | Pauli exclusion principle |
Nuclear and particle
Name the force before naming the particle: the strong force holds quarks and nuclei, the weak force changes one quark into another (every beta decay), electromagnetism handles everything charged.
| Clue in the question | Answer |
|---|---|
| Carrier of the strong / electromagnetic / weak force | Gluon / photon (no charge, no mass) / W and Z bosons |
| Beta-minus / positron emission | Neutron → proton + electron + electron antineutrino / proton → neutron + positron + neutrino |
| Quark charges | Up, charm, top: +2/3; down, strange, bottom: −1/3; proton = uud, neutron = udd |
| Stopped by paper / aluminum / thick lead | Alpha (smoke detectors) / beta / gamma — most ionizing is least penetrating |
| Relativity: light from a moving source / moving clock / moving ship | Still travels at c / runs slow / shorter along its motion |
Units
Rebuild an unfamiliar unit from the simplest formula that contains the quantity: E = hf makes Planck's constant J·s; RC = (V/A)(C/V) = seconds.
| Clue in the question | Answer |
|---|---|
| Tesla / weber / henry / siemens | Magnetic field / magnetic flux / inductance / conductance |
| Volt per ampere / newton-meter | Ohm / joule (as work; torque stays N·m) |
| Entropy / momentum | J/K / kg·m/s, the same as N·s |
More than half of Physics short-answer questions are calculations, and the numbers are chosen to come out clean. These patterns skip most of the algebra.
| Question type | Shortcut |
|---|---|
| Scaling with distance | Gravity, Coulomb force, point-source intensity: 1/r2; potential energy, potential, field of a wire: 1/r; field of a flat sheet: no change |
| Other scalings | KE ∝ v2; blackbody power ∝ T4; wave speed on a string ∝ √tension; SHM energy ∝ amplitude2 |
| Decibels | +10 dB = ×10 intensity; +3 dB = ×2; 70 → 100 dB = ×1000 |
| Straight up and back down (g = 10) | Time up = v/g; max height = v2/(2g): 100 m/s → 500 m; 12 s round trip → 6 s up → 180 m |
| Projectile: time to the top | v sin θ / g: 60 m/s at 30° → 3 s |
| Two resistors in parallel / n identical ones | Product over sum (3 and 6 → 2) / R/n; capacitors in series follow the same rules |
| Hydrogen energy levels | En = −13.6/n2 eV; work in fractions: 1→2 is 3/4, 2→3 is 5/36 of 13.6 |
| Relativity at 0.6c / 0.8c | 3-4-5 triangle: time stretches by 5/4 / 5/3; length shrinks by 4/5 / 3/5 |
Out of time on a multiple-choice question? A wrong answer after the question is read costs nothing, so guess. Y is the most common answer in Physics (27%) and W the least (23%).