Schleswig-Holstein Abitur Physics common mistakes
Schleswig-Holstein Abitur Physics · Understand the traps and how to avoid them.
In kinematics tasks, students add or subtract velocities without fixing a positive direction first, so a braking car or a ball thrown upward ends up with a sign error and a physically impossible result (e.g. negative time or a distance that grows while the object decelerates).
The formula v = v₀ + a·t is memorized as a string of symbols, and students plug in magnitudes because the task text gives numbers without arrows. They treat acceleration as 'always positive' rather than as a vector component, and they do not sketch the motion.
What to do instead
Before calculating, draw a coordinate axis with the positive direction marked and write every given quantity with an explicit sign (v₀ = +20 m/s, a = −4 m/s²). Check the sign of the result against the sketch: a decelerating object must reach v = 0 at t = v₀/|a|. Practise one braking problem and one upward-throw problem per session until the sign convention is automatic.
In Newtonian dynamics, students set the driving force equal to the net force in problems with friction, an inclined plane, or a lift, and then compute an acceleration that ignores one of the forces. A typical error is writing F = m·a with F = F_pull while friction also acts.
Free-body diagrams are skipped because they feel like extra work, and the equation F = m·a is applied to whatever single force is mentioned in the text. Students also confuse the force exerted by a surface with the weight, or forget that the normal force on an incline is m·g·cos α, not m·g.
What to do instead
Always draw the free-body diagram first, one arrow per force with a label, then choose axes (along and perpendicular to the motion) and write ΣF = m·a only for the chosen direction. For inclines, resolve weight into m·g·sin α along the slope and m·g·cos α perpendicular to it. Verify with a limiting case: with zero friction the acceleration must equal g·sin α.
In circular motion and gravitation, students use the wrong radius (the height above the surface instead of the distance from the centre) or forget that the centripetal force is the resultant of the real forces rather than an additional force to be added to the diagram.
Texts give 'altitude 400 km' and students insert 400 km into F = G·m·M/r². The phrase 'centripetal force' suggests a new force, so it gets drawn alongside gravity, and the resulting equation double-counts. Satellite and orbital problems are also treated as statics.
What to do instead
Write r = R_Earth + h explicitly and state R_Earth ≈ 6.37·10⁶ m before substituting. For any circular motion, list the real forces, then set their resultant (toward the centre) equal to m·v²/r; never add a separate 'centripetal force' arrow. Sanity-check with the orbital speed at low altitude, about 7.9 km/s.
In conservation-law problems (momentum, energy), students apply conservation to a process where it does not hold - e.g. using energy conservation in a perfectly inelastic collision, or momentum conservation when an external force acts during the interval - and they mix up the system boundary between the two.
Both laws look like 'before equals after' equations, so students pick whichever is convenient. The conditions (no net external force for momentum; no non-conservative work for mechanical energy) are stated once in class and then dropped, and the choice of system is rarely written down.
What to do instead
Before writing any conservation equation, state in one sentence which system you choose and which quantity is conserved and why ('momentum conserved: collision time short, external forces negligible; mechanical energy not conserved: deformation'). For inelastic collisions compute the energy loss explicitly as ΔE = E_before − E_after and interpret it as deformation/heat.
In electric and magnetic field problems, students compute the Lorentz force magnitude but ignore the direction rule, or treat the magnetic force as doing work and changing the particle's speed. They also confuse field lines with particle trajectories.
The cross product F = q·v×B is reduced to F = q·v·B·sin α with α guessed, and the right-hand rule is applied without checking the sign of the charge. Because the force is always perpendicular to v, students assume it accelerates the particle along its path.
What to do instead
For every Lorentz-force problem, sketch v and B, apply the right-hand rule, then reverse the result for negative charges. State explicitly that the magnetic force is centripetal: it changes direction but not speed, so |v| is constant and the path is a circle with r = m·v/(|q|·B). Verify with a known case such as an electron in a 1 mT field.
In induction problems, students use Φ = B·A without the cosine of the angle between field and area normal, or they compute the induced voltage but not its direction, and they forget that only a changing flux produces an EMF.
The formula is memorized as a product of two magnitudes, and the angle dependence is invisible when the diagram shows a coil 'in' a field. Lenz's law is treated as a vocabulary item rather than a sign rule, and static situations are mistakenly treated as inducing a voltage.
What to do instead
Write Φ = B·A·cos α with α defined as the angle between B and the area normal, and note which quantity actually varies with time. Apply Lenz's law by asking 'which direction of induced current would oppose the change?' and check with the right-hand rule. Include one problem where the coil is stationary in a constant field, so the answer is U_ind = 0.
In oscillation and wave problems, students use the angular frequency ω and the frequency f interchangeably, and they add amplitudes of two superposed waves arithmetically even when the phase difference is neither 0 nor π.
ω = 2π·f is learned as a formula but not as a distinction, so T = 2π/ω and T = 1/f get mixed. Superposition is taught mainly through the two extreme cases (constructive and destructive), so students assume amplitudes always add or always cancel and ignore the phase.
What to do instead
Always write the oscillation as x(t) = A·sin(ω·t + φ) and label ω in rad/s and f in Hz, converting explicitly. For superposition, compute the phase difference Δφ = 2π·Δs/λ first and then use the general result (phasor or the cosine rule for amplitudes); reserve simple addition for Δφ = 0 and subtraction for Δφ = π. Check the limiting cases.
In interference and diffraction problems, students use the single-slit minimum condition and the double-slit maximum condition interchangeably, or they forget that the path difference must be expressed in wavelengths, not in centimetres.
Both situations produce 'dark and bright fringes' and the formulas d·sin θ = k·λ and b·sin θ = k·λ look nearly identical. Students also plug distances in different units into the same equation, and they use the small-angle approximation sin θ ≈ tan θ without checking that the angle is small.
What to do instead
Label each problem as 'double slit (two sources, maxima at d·sin θ = k·λ)' or 'single slit (one aperture, minima at b·sin θ = k·λ)' before substituting. Convert every length to metres and compute λ in metres. Verify the small-angle approximation by estimating θ; if θ > about 10°, use the exact sine and the geometry of the screen distance.
In quantum and atomic physics, students apply the photoelectric equation with the wrong quantity as threshold - using the work function W as if it were the stopping voltage, or confusing the photon energy h·f with the maximum kinetic energy of the electron - and they treat the Bohr model as literally correct rather than as a model with limits.
The equation E_kin,max = h·f − W contains three energies that all appear in the same problem, and the units (eV vs J) invite errors. The Bohr model is often presented as the explanation of spectra, so students do not distinguish its successful predictions (hydrogen energy levels) from its failures (multi-electron atoms, fine structure).
What to do instead
Write the energy balance as a labelled line: photon energy h·f → work function W (escape) → remaining maximum kinetic energy e·U_stop. Convert eV and J explicitly (1 eV = 1.602·10⁻¹⁹ J). When asked to evaluate the Bohr model, name one prediction it gets right (hydrogen line series) and one phenomenon it cannot explain (helium spectrum, Zeeman splitting), and state that the modern description is the quantum-mechanical orbital model.
In nuclear and relativity problems, students balance charge but not nucleon number (or vice versa) in decay equations, and they apply time dilation or length contraction with the proper time assigned to the wrong frame or with the Lorentz factor inverted.
Decay equations are written quickly as symbol substitutions without a conservation check. In relativity, the terms 'proper time' and 'proper length' are memorized as definitions but not tied to the physical criterion (measured in the rest frame of the clock or the object), so the factor γ is applied in the wrong direction. Unit handling of u, MeV and c = 1 conventions adds errors.
What to do instead
For every decay or reaction, write the equation with mass numbers and atomic numbers above and below each symbol and check both sums before moving on. For relativity, identify the rest frame first and label it; then Δt = γ·Δt₀ and L = L₀/γ, with γ ≥ 1 always. Check the direction of the effect: a moving clock must run slow, and a moving object must appear shortened. Do the mass-energy conversion with 1 u = 931.5 MeV/c² explicitly.