Slovakia Maturita Physics common mistakes
Slovakia Maturita Physics · Understand the traps and how to avoid them.
When combining velocities or forces, adding magnitudes arithmetically (e.g. writing v = v1 + v2 for perpendicular or arbitrary angles) instead of adding them as vectors.
Everyday experience treats speeds as simple numbers, and students memorize 'add the speeds' without tracking direction; the vector nature of velocity and force is under-practiced.
What to do instead
Before any addition, draw a sketch with arrows and choose axes; resolve each vector into components, add components separately, then recombine with Pythagoras and arctan. Always state direction alongside magnitude.
Applying conservation of mechanical energy to situations with friction or other non-conservative forces without including the work done against them, so the final speed comes out too high.
The energy-conservation formula is drilled on frictionless inclined planes, and students pattern-match 'height given, find speed' without checking whether energy leaves the system.
What to do instead
First list all forces and mark which are conservative; if any non-conservative force acts, write E1 + W_nc = E2 and compute W_nc = F·d·cosθ explicitly. Check plausibility: with friction the speed must be lower than the frictionless result.
Treating temperature and heat as the same quantity, e.g. saying a body 'contains heat' or adding temperatures when mixing, instead of using calorimetry Q = mcΔT and setting heat lost equal to heat gained.
Everyday language conflates 'hot' with 'heat', and the distinction between a state variable (T, internal energy) and a process quantity (Q, W) is abstract and easily glossed over.
What to do instead
For every mixing problem write a heat-balance equation: sum of Q for components = 0, with signs from ΔT. Define in one sentence the difference between temperature (average kinetic energy per particle) and heat (energy transferred due to ΔT).
Using the ideal-gas law with temperature in degrees Celsius, or mixing units (pressure in kPa with volume in cm³) without converting to SI.
The formula pV = nRT is memorized but the requirement that T be absolute and units be consistent is treated as a detail; students plug numbers straight from the assignment.
What to do instead
Adopt a fixed routine: convert every given quantity to SI first (T → kelvin by adding 273.15, cm³ → m³ by ×10⁻⁶, kPa → Pa by ×10³), write the unit next to each substituted number, then compute.
Confusing series and parallel rules for resistors (and by analogy capacitors), e.g. adding resistances directly in a parallel branch or assuming current is the same everywhere in a parallel circuit.
The two rule sets are mirror images and are learned close together; without a physical picture of how current splits at junctions, the formulas get swapped under exam pressure.
What to do instead
Anchor the rules in physics: in series the same current flows and voltages add (R_eq = ΣR); in parallel the same voltage is across each branch and currents add (1/R_eq = Σ1/R). Redraw the circuit and label current at each junction before calculating.
Applying Ohm's law to a whole circuit while ignoring internal resistance or the distinction between terminal voltage and EMF, giving a current that is too large.
Textbook drills use ideal sources, so the internal resistance term ε = I(R + r) feels like an optional extra and is dropped.
What to do instead
For any real source, write the full-loop equation ε = I(R + r) and separately U_terminal = ε − Ir. If the problem mentions a battery with internal resistance, always include r in the loop and check that U_terminal < ε.
Drawing ray diagrams for lenses or mirrors with rays that do not obey the rules (e.g. a ray through the centre bending, or a parallel ray not passing through the focal point), leading to a wrong image position or type.
Students sketch 'something that looks like optics' from memory rather than applying the three standard construction rays, and they do not cross-check the drawing against the thin-lens equation.
What to do instead
Always use the three canonical rays (parallel→focus, through centre→straight, through focus→parallel) and then verify with 1/f = 1/a + 1/a′; check the sign convention and confirm real/virtual and upright/inverted from both the diagram and the sign of a′.
Treating the period of a pendulum as depending on mass or amplitude, or confusing angular frequency ω with frequency f in SHM formulas.
The formula T = 2π√(l/g) is recalled approximately, and ω = 2πf is a conversion students forget to apply, so answers are off by a factor of 2π.
What to do instead
Memorize that a simple pendulum's period depends only on length and g (for small angles), and always write the bridge ω = 2π/T = 2πf before substituting. Sanity-check: doubling the mass must not change T.
Mixing up the photoelectric-effect relationships, e.g. claiming intensity changes the maximum kinetic energy of emitted electrons or that frequency changes the current, or using E = hf with f in the wrong units.
The dual roles of intensity (number of photons) and frequency (energy per photon) are counter-intuitive, and h is small so unit errors (nm vs m) are common.
What to do instead
State the two separate statements explicitly: intensity → number of photoelectrons (current); frequency → maximum kinetic energy via hf = W + E_k,max. Convert wavelength to metres and use E = hc/λ when λ is given.
Confusing mass and weight, or mixing up the astronomical unit, light-year and parsec, and using the wrong scale for distances in the Solar System versus interstellar space.
Everyday usage says 'weight in kilograms', and the three distance units are introduced together without a felt sense of their relative size.
What to do instead
Keep a one-line reference table: 1 AU ≈ 1.5×10¹¹ m (Solar System), 1 ly ≈ 9.46×10¹⁵ m, 1 pc ≈ 3.26 ly; weight = mg in newtons. Before answering, ask whether the object is inside the Solar System (AU) or beyond it (ly/pc).