NCEA Level 3 Physics - Achievement Standards
This section covers the Level 3 Physics achievement standards, which test your ability to explain and apply physics models in wave systems, mechanical systems, modern physics and electrical systems, and to carry out a practical investigation and apply physics in a selected context. External questions reward choosing the right model, showing the reasoning from evidence to equation, and reporting units and significant figures consistently.
Core models and rules
- Mechanical systems: for uniform circular motion the net force points to the centre; v = 2πr/T and a_c = v²/r. In simple harmonic motion a = −ω²y and ω = 2π/T; energy alternates between kinetic and potential while total energy stays constant for an ideal oscillator.
- Wave systems: interference depends on path difference measured in wavelengths; nodes occur where waves cancel. Diffraction is most noticeable when the wavelength is comparable to the gap or obstacle. For sound or light with v ≪ c, the Doppler shift is approximated by Δf/f ≈ v/c.
- Electrical systems: Q = CV and E = ½CV² for capacitors; inductors oppose changes in current. Faraday’s law links induced emf to the rate of change of magnetic flux, and Lenz’s law gives the direction opposing the change.
- Modern physics: photon energy E = hf; the photoelectric effect needs f above a threshold frequency, and atomic spectra come from discrete energy levels.
- Practical/context work: identify independent and dependent variables, controls and uncertainty, then justify the physics used in the unfamiliar context.
Worked example
A 0.50 kg mass on a spring has period 0.80 s and amplitude 0.12 m. Maximum speed is v_max = ωA, where ω = 2π/T = 2π/0.80 = 7.85 rad/s, so v_max = 7.85 × 0.12 = 0.94 m/s. This occurs at equilibrium, where displacement and acceleration are zero. Maximum acceleration is a_max = ω²A = 7.4 m/s², directed opposite the displacement.
Traps
Using diameter instead of radius in circular motion; mixing period and frequency; dropping the minus sign in SHM; forgetting the ½ in capacitor energy; reversing Lenz’s law; and giving answers without units or with too many significant figures.