Practice · concept traps
The 120 places marks are lost.
Not a list of formulas — a list of the specific wrong turns that cost marks in each chapter, pulled together from all thirty. Every line is the chapter's own pitfalls note, so each one links back to the section that fixes it and to the printable card it lives on.
Sorted by the kind of mistake rather than by chapter, because the kinds repeat: the sign convention you drop in optics is the one you dropped in thermodynamics.
Two quantities confused
38 trapsTwo neighbours swapped for each other — speed for velocity, flux for its rate of change, H for B.
I · 01The Calculus Toolkit
Reading area under a v–t graph as distance. It is displacement; distance needs |v|.Common Pitfalls: What the Examiner Traps Reveal
🔒 Reader ▸Card ▸I · 02Kinematics in One Dimension
“40 km/h out, 60 back, average 50.” No — total distance ÷ total time gives 48, and the average velocity is zero.The Average Speed Trap
🔒 Reader ▸Card ▸I · 04Newton's Laws of Motion
“Friction opposes motion.” It opposes relative sliding — walking and pedalling are driven by it.Friction
🔒 Reader ▸Card ▸I · 04Newton's Laws of Motion
Confusing apparent with true weight. The scale reads N; in a lift accelerating up that is m(g + a).Common JEE / NEET Pitfalls
🔒 Reader ▸Card ▸I · 05Work, Energy and Power
W = F d cos θ uses the displacement of the point of application — friction's work uses the path length.Work Done by a Force
Reader ▸Card ▸I · 09Gravitation
“Astronauts float because there is no gravity.” g ≈ 8.7 m s−2 at the ISS; they are in free fall.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 10Fluid Mechanics
Treating ρgh as the absolute pressure. It is gauge — absolute is p0 + ρgh.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 10Fluid Mechanics
Using the total volume in Archimedes for a floating body — only Vsub counts.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 11Properties of Matter
Comparing wires by breaking force. Compare the stress σ = F/A before deciding which fails first.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 11Properties of Matter
Comparing extensions instead of strain. A longer wire of the same material extends more.Stress and Strain: The Right Variables
Reader ▸Card ▸II · 01Simple Harmonic Motion
Taking the amplitude as the initial position. With both x0 and v0 non-zero, get A from energy.Energy in SHM
🔒 Reader ▸Card ▸II · 02Waves and Sound
Using the wave speed as the particle speed. The medium's element peaks at Aω; the pattern travels at ω/k.Speed of a Wave
🔒 Reader ▸Card ▸II · 02Waves and Sound
Swapping displacement and pressure. An open end is a displacement antinode and a pressure node.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 01Thermal Properties of Matter
Reading the rise in liquid level as the real expansion. It is apparent — add back 3α of the vessel.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 01Thermal Properties of Matter
Thinking a heated plate's hole shrinks. Every dimension scales by (1 + αΔT), the cavity included.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 02The Laws of Thermodynamics
Reading “isothermal” as “no heat flows”. ΔU = 0 gives Q = W; it is adiabatic that gives Q = 0.Specific Heats of Gases: C_P, C_V, and \gamma
🔒 Reader ▸Card ▸III · 03Kinetic Theory of Gases
Using v̄ in the pressure formula or vrms in Graham's law. Pressure and energy take vrms; effusion takes v̄.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 03Kinetic Theory of Gases
Believing viscosity rises with pressure. At fixed T, η is pressure-independent because n ∝ p and λ ∝ 1/p cancel — λ itself is not: λ = kT/(√2 σp).Mean Free Path and Collision Rate
🔒 Reader ▸Card ▸IV · 01Ray Optics
Inverting the apparent-depth ratio. It is (observer-side index) ÷ (object-side index), always.Refraction and Snell's Law
Reader ▸Card ▸IV · 02Wave Optics
Reading a sin θ = nλ as a maximum. For one slit it locates the minima; for two slits d sin θ = nλ is a maximum.Diffraction at a Single Slit
🔒 Reader ▸Card ▸IV · 02Wave Optics
Quoting the vacuum wavelength inside a liquid. In a medium λ → λ/n, and β shrinks with it.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 01Electrostatics
Reading V = 0 as E = 0. On a dipole's equator the potentials cancel while the field vectors add.The Dipole: Potential, Field, and Energy
🔒 Reader ▸Card ▸V · 01Electrostatics
Reading E = 0 as V = 0. Inside a conductor the field vanishes and the potential is a non-zero constant.Relation Between the Field and the Potential
🔒 Reader ▸Card ▸V · 02Current Electricity
Confusing resistivity with resistance. Stretching a wire changes R, never ρ.Putting It Together — Circuit Strategy
🔒 Reader ▸Card ▸V · 04Magnetism and Matter
Reading zero net force as nothing happening. In a uniform field a dipole feels no force but a real torque.Force and Torque on a Magnetic Dipole in a Magnetic Field
Reader ▸Card ▸V · 04Magnetism and Matter
Asking where a magnetic field line begins. It does not — inside the magnet it runs S → N and closes.Force and Torque on a Magnetic Dipole in a Magnetic Field
Reader ▸Card ▸V · 04Magnetism and Matter
Substituting H for B in a force or torque. Those take B; inserting a core changes B, never H.Force and Torque on a Magnetic Dipole in a Magnetic Field
Reader ▸Card ▸V · 05Electromagnetic Induction
Reading a large flux as a large emf. Only the rate of change induces; steady flux induces nothing.Electromagnetic Induction: Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 06Alternating Current
Thinking L and C vanish at resonance. Their reactances cancel; VL and VC are each Q times the supply.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 07Electromagnetic Waves
Treating displacement current as charge crossing the gap. It is a rate of change of electric flux.The Need for Displacement Current
Reader ▸Card ▸V · 07Electromagnetic Waves
Changing the frequency in a medium. Speed and wavelength drop by n; the frequency is set by the source.Speed of Electromagnetic Waves
🔒 Reader ▸Card ▸V · 07Electromagnetic Waves
Imagining E and B take turns. They oscillate in phase and carry half the energy each.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 01Dual Nature of Radiation and Matter
Expecting a brighter source to give faster electrons. Intensity sets the current; frequency sets Kmax.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 03Semiconductor Electronics
Expecting a semiconductor to behave like a weak metal. Its resistance falls as the temperature rises.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 03Semiconductor Electronics
Calling n-type silicon negatively charged. Each donor leaves a fixed positive ion — the material is neutral.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 04Nuclei
Ranking stability by total binding energy. Uranium's is larger than iron's; iron is the more stable per nucleon.Binding Energy and the Curve of Stability
Reader ▸Card ▸VI · 04Nuclei
Believing the β− electron was already inside. It is created in the decay n → p + e− + ν.Radioactivity: Alpha, Beta, and Gamma Decay
🔒 Reader ▸Card ▸VI · 04Nuclei
Reading a long half-life as a strong source. A = λN, so a longer t½ means less activity.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸Formula outside its range
24 trapsA correct formula used where its conditions fail. The algebra is clean and the answer is wrong.
I · 03Vectors & Motion in a Plane
Using R = u² sin 2θ / g when the launch and landing points are at different heights. It does not apply.Projectile Motion
🔒 Reader ▸Card ▸I · 04Newton's Laws of Motion
Writing fs = μsN always. That is the limit: push a stuck block with 10 N and friction is 10 N.Friction
🔒 Reader ▸Card ▸I · 04Newton's Laws of Motion
Taking N = mg. True only on the level with no other vertical force — on an incline N = mg cos θ.Common JEE / NEET Pitfalls
🔒 Reader ▸Card ▸I · 05Work, Energy and Power
“The normal force never does work.” Only while the surface is still: a moving wedge or a lift floor does.Work Done by a Force
Reader ▸Card ▸I · 06Circular Motion
Writing T = mg for a conical pendulum. It is T = mg/cos θ — twice the weight at 60°.The Conical Pendulum
🔒 Reader ▸Card ▸I · 06Circular Motion
Using vtop = √(gL) for a rod. A rod can push, so the condition is only v ≥ 0.Common Pitfalls in Circular Motion
🔒 Reader ▸Card ▸I · 08Rotational Mechanics
Using the perpendicular-axis theorem on a solid body. It holds for plane laminae only.The Parallel Axis Theorem
🔒 Reader ▸Card ▸I · 09Gravitation
Carrying g = 9.8 onto another planet. G is universal; g = GM/R² is local — recompute it.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 09Gravitation
Using mgh at orbital altitude. Past about 100 km the error already exceeds 3 % — use −GMm/r.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 09Gravitation
Applying T² ∝ a³ across different central bodies. The constant carries the mass M you orbit.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸I · 10Fluid Mechanics
Applying Bernoulli between points not on one streamline. Trace the streamline before you equate.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸II · 01Simple Harmonic Motion
Assuming T is amplitude-independent for a pendulum at 30° or 60°. The θ₀²/16 correction adds 0.4 % at 15°, 1.7 % at 30° and about 7 % at 60°.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 01Thermal Properties of Matter
Omitting latent heat in a mixing problem. Check whether the heat available finishes the phase change.Latent Heat and Phase Transitions
🔒 Reader ▸Card ▸III · 02The Laws of Thermodynamics
Writing Q = n CV ΔT for an adiabatic compression. Q = 0 there, whatever ΔT is.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸IV · 01Ray Optics
Applying a critical angle going rarer → denser. Total internal reflection needs n1 > n2 and θ > θc.Total Internal Reflection
🔒 Reader ▸Card ▸V · 02Current Electricity
Forgetting the internal resistance. A cell's terminal voltage equals its emf only at zero current.Cells, EMF, and Internal Resistance
🔒 Reader ▸Card ▸V · 02Current Electricity
Using V = IR across a capacitor branch in the steady state. No current flows there — it is an open circuit.Charging and Discharging a Capacitor: the RC Circuit
🔒 Reader ▸Card ▸V · 03Moving Charges and Magnetism
Expecting a force on a stationary charge. F = q(v × B) vanishes at v = 0 — ask for the velocity first.Magnetic Force on a Moving Charge
Reader ▸Card ▸V · 04Magnetism and Matter
Using χ = C/T just above the Curie point. A ferromagnet obeys C′/(T − TC) there.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 05Electromagnetic Induction
Letting the current in an inductor jump. It is continuous: at switch-on I = 0, at switch-off it decays.Growth and Decay of Current in an RL Circuit
🔒 Reader ▸Card ▸VI · 01Dual Nature of Radiation and Matter
Using λ = h/mv with a relativistic speed, or with the total energy in place of the kinetic energy.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 01Dual Nature of Radiation and Matter
Forgetting that below the threshold frequency nothing is emitted at all — no intensity can rescue it.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 02Atoms
Dropping the Z² when the ion is not hydrogen — He+ ionises at 54.4 eV, not 13.6.Radii, Speeds, and Energies of Hydrogen-Like Atoms
🔒 Reader ▸Card ▸VI · 05Special Relativity
Calling a 1.6c closing speed a velocity. Use the addition law for the relative speed; it stays under c.Relativistic Velocity Addition
🔒 Reader ▸Card ▸Frame, axis or route wrong
18 trapsThe physics is fine; the choice made before the first line of algebra was not.
I · 01The Calculus Toolkit
Using a = v dv/dx when acceleration is given as a function of time — that route needs a = dv/dt.Common Pitfalls: What the Examiner Traps Reveal
🔒 Reader ▸Card ▸I · 02Kinematics in One Dimension
Writing all three equations and hoping. Name the variable you neither know nor need, and use the one that omits it.The Average Speed Trap
🔒 Reader ▸Card ▸I · 03Vectors & Motion in a Plane
“Launched at 30° to the incline” means θ = 30° + α from the horizontal — not 30°. A favourite JEE trap.Projectile on an Inclined Plane
🔒 Reader ▸Card ▸I · 03Vectors & Motion in a Plane
In river problems the boat's speed is given relative to the water, never to the bank.Relative Motion in Two Dimensions
🔒 Reader ▸Card ▸I · 05Work, Energy and Power
Using energy to find a time. Energy relates speeds to positions; time enters only through kinematics.Common Pitfalls: A Field Guide to WEP Errors
Reader ▸Card ▸I · 06Circular Motion
Drawing a separate Fc arrow in the FBD. It is the resultant of the real forces, not an extra one.Common Pitfalls in Circular Motion
🔒 Reader ▸Card ▸I · 07Centre of Mass, Momentum & Collisions
Forgetting that e is defined along the line of impact, not along the original velocity.Common Pitfalls and Exam Traps
🔒 Reader ▸Card ▸I · 08Rotational Mechanics
Writing two correct equations about two different axes. Choose the axis first, then keep it.Pitfalls
🔒 Reader ▸Card ▸I · 08Rotational Mechanics
Quoting I without naming the axis. MR²/2 is a disc about its centre and nowhere else.Pitfalls
🔒 Reader ▸Card ▸I · 11Properties of Matter
Series and parallel backwards. End-to-end: same force. Side by side: same extension.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸II · 01Simple Harmonic Motion
Measuring x from the spring's natural length on a vertical spring. It oscillates about the stretched equilibrium.Spring–Mass Systems
🔒 Reader ▸Card ▸II · 01Simple Harmonic Motion
Using k1 + k2 for springs in series — that is the parallel result.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 01Electrostatics
Using U = ½CV² after the battery is disconnected. Ask first which quantity is fixed — V or Q.Common Pitfalls · Charges & Fields
🔒 Reader ▸Card ▸V · 02Current Electricity
Putting an ammeter in parallel or a voltmeter in series. Ammeter: series, low R. Voltmeter: parallel, high R.From Galvanometer to Ammeter and Voltmeter
🔒 Reader ▸Card ▸V · 03Moving Charges and Magnetism
Using the angle the coil's plane makes with B in τ = NIAB sin θ. θ is measured from the normal.Moving Coil Galvanometer
🔒 Reader ▸Card ▸VI · 03Semiconductor Electronics
Reading the 0.7 V drop as a source. The external circuit sets the current: I = (Vsupply − 0.7)/R.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 05Special Relativity
Not naming the proper time. Δt0 is read by the single clock present at both events.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 05Special Relativity
Reading mutual time dilation as a contradiction. The frames disagree about simultaneity by v x/c².Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸A factor or a power wrong
13 trapsThe structure is right and a 2, a ½, a √2 or an exponent is not — the classic single-mark loss.
I · 01The Calculus Toolkit
Forgetting + C on an indefinite integral, then losing the initial condition that fixes it.Common Pitfalls: What the Examiner Traps Reveal
🔒 Reader ▸Card ▸I · 10Fluid Mechanics
Halving a pipe's radius and halving the flow. Q ∝ R4: it falls by a factor of 16.Viscosity and Poiseuille Flow
🔒 Reader ▸Card ▸I · 11Properties of Matter
Dropping the ½ in U = ½ F ΔL. The force builds from zero, so the average is F/2.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸II · 02Waves and Sound
Writing fbeat = (f1 − f2)/2. That is the modulation rate; the beats heard are |f1 − f2|.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 03Kinetic Theory of Gases
Dropping the √2 from the collision frequency. It comes from the mean relative speed and is worth 41 %.Mean Free Path and Collision Rate
🔒 Reader ▸Card ▸III · 03Kinetic Theory of Gases
Reading γ = 7/5 as f = 7. A diatomic gas has f = 5; the 7 is f + 2. Use γ = 1 + 2/f.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 05Electromagnetic Induction
Taking L ∝ N for a solenoid. It goes as N² — double the turns and the inductance quadruples.Electromagnetic Induction: Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 06Alternating Current
Reading “zero mean” as “zero power”. Power follows v², whose average is V0²/2.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 07Electromagnetic Waves
Using I/c for a mirror. A perfect reflector feels 2I/c; reflectivity R gives (1 + R)I/c.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 02Atoms
Writing tan(θ/2) for the impact parameter. It is cot.The Nuclear Atom: Closest Approach and Impact Parameter
Reader ▸Card ▸VI · 03Semiconductor Electronics
Using the mains frequency as the ripple frequency. A full-wave rectifier ripples at 2f.The Diode as a Rectifier
🔒 Reader ▸Card ▸VI · 04Nuclei
Saying two half-lives empty the sample. A quarter remains, and it never reaches zero.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 05Special Relativity
Getting γ the wrong way up. Time multiplies by γ, length divides — moving clocks slow, moving rods short.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸Vector treated as a number
8 trapsMagnitudes added where components, directions or phasors were required.
I · 02Kinematics in One Dimension
Adding components arithmetically. Speed is √(vx² + vy²), never vx + vy.The Average Speed Trap
🔒 Reader ▸Card ▸I · 02Kinematics in One Dimension
Calling the velocity zero at the top of a throw. Only vy is zero; vx survives untouched.The Average Speed Trap
🔒 Reader ▸Card ▸I · 03Vectors & Motion in a Plane
Adding magnitudes instead of vectors. |A + B| = A + B only when they are parallel.The Position Vector in 2D
🔒 Reader ▸Card ▸I · 06Circular Motion
Reading constant ω as zero acceleration. at is zero; ac = ω²r is not.Common Pitfalls in Circular Motion
🔒 Reader ▸Card ▸I · 07Centre of Mass, Momentum & Collisions
Using scalar momentum in two dimensions. Conserve x and y separately.Collisions in Two Dimensions
🔒 Reader ▸Card ▸IV · 02Wave Optics
Adding intensities for coherent beams. Add amplitudes and square, or the dark fringe never reaches zero.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 01Electrostatics
Adding fields as magnitudes. Only collinear contributions add that way — otherwise resolve first.Common Pitfalls · Charges & Fields
🔒 Reader ▸Card ▸V · 06Alternating Current
Adding R, XL and XC arithmetically. Z = √(R² + (XL − XC)²).Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸Units, kelvin and radians
7 trapsCelsius in a formula that wants kelvin, degrees where radians are assumed, eV mixed with joules.
I · 01The Calculus Toolkit
Differentiating sin x with x in degrees. The rule (sin x)′ = cos x holds only in radians.Common Pitfalls: What the Examiner Traps Reveal
🔒 Reader ▸Card ▸II · 02Waves and Sound
Adding decibels. 60 dB and 60 dB give 63 dB — convert to intensity, add, convert back.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 01Thermal Properties of Matter
Celsius in a formula with a standalone T. p V = n R T, σT4 and λmT = b all need kelvin.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸III · 02The Laws of Thermodynamics
Celsius in η = 1 − TC/TH. The round-number answer is the lure — convert to kelvin first.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 06Alternating Current
Writing XL = f L. It is ω L — at 50 Hz that is 314, not 50, and the answer is out by 2π.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 01Dual Nature of Radiation and Matter
Mixing electron-volts with joules mid-calculation. Work in eV and nm, with hc = 1240 eV nm.Electron Emission and the Work Function
Reader ▸Card ▸VI · 02Atoms
Mixing eV with metres. Use λ(nm) = 1240/E(eV) and stop converting.The Nuclear Atom: Closest Approach and Impact Parameter
Reader ▸Card ▸Sign and convention
7 trapsWhich way is positive, decided once and kept — or decided at the end and guessed.
III · 02The Laws of Thermodynamics
Importing the chemistry convention ΔU = Q + W. Here W is work done by the gas: ΔU = Q − W.Work Done by a Gas
🔒 Reader ▸Card ▸IV · 01Ray Optics
Plugging in magnitudes and fixing the sign at the end. Assign every sign from the data and let the algebra answer.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸IV · 01Ray Optics
Carrying the mirror's m = −v/u into a lens problem. For a lens m = + v/u — memorise the pair together.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸IV · 02Wave Optics
Dropping the λ/2 at a denser-medium reflection. Every bright and dark condition inverts with it.Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸V · 03Moving Charges and Magnetism
Expecting parallel currents to repel by analogy with like charges. They attract — use the right-hand rule.Force Between Two Parallel Current-Carrying Conductors
🔒 Reader ▸Card ▸V · 05Electromagnetic Induction
Dropping Lenz's minus sign and getting the induced current's direction backwards.Electromagnetic Induction: Common Pitfalls and Exam Strategy
🔒 Reader ▸Card ▸VI · 02Atoms
Confusing “energy of the level” (negative) with “energy needed to remove” (positive).Radii, Speeds, and Energies of Hydrogen-Like Atoms
🔒 Reader ▸Card ▸Conservation misapplied
5 trapsA conservation law or theorem invoked over an interval where it does not hold.
I · 05Work, Energy and Power
Setting the work of one force equal to ΔK. The theorem sums the work of every force.The Work–Energy Theorem
Reader ▸Card ▸I · 07Centre of Mass, Momentum & Collisions
Conserving momentum through the sliding after a collision. Friction is negligible only during the impact.Linear Momentum and Its Conservation
🔒 Reader ▸Card ▸I · 07Centre of Mass, Momentum & Collisions
Writing both Pi = Pf and Ki = Kf for an inelastic collision. They contradict.Common Pitfalls and Exam Traps
🔒 Reader ▸Card ▸I · 08Rotational Mechanics
Letting rolling friction dissipate energy. The contact point does not move, so its work is zero.Pitfalls
🔒 Reader ▸Card ▸V · 03Moving Charges and Magnetism
Letting a magnetic field speed a particle up. It is always ⊥ to v, so it does no work at all.Motion of a Charged Particle in a Uniform Magnetic Field
Reader ▸Card ▸Where these come from
Each chapter closes on a pitfalls section, and each chapter's printable formula card carries a “where marks are lost” box drawn from it. This page is those boxes, unpacked and cross-cut. The cards are free — all thirty of them.