Physics
Physics combines theory with laboratory work. The written paper tests mechanics, gravitation, thermodynamics, oscillations, waves, electrostatics, current electricity, magnetism, optics and modern physics. Numerical answers need units, direction and a sensible number of significant figures.
Core rules and concepts
- Mechanics: draw a free-body diagram; resolve forces; apply Newton's second law or conservation of energy.
- Circuits: use Ohm's law, Kirchhoff's rules and power relations; check series/parallel combinations before substituting.
- Optics: follow the sign convention consistently; use the lens or mirror formula and magnification together.
- Modern physics: apply Einstein's photoelectric equation and conservation of charge and nucleon number.
- Units: convert cm to m, g to kg and minutes to seconds before calculation.
Worked example: work-energy
A 2 kg object starts from rest under a constant 6 N force for 4 s. Acceleration a = F/m = 3 m/s². Velocity v = u + at = 12 m/s. Displacement s = ½at² = 24 m. Work done W = Fs = 6 × 24 = 144 J. Check by kinetic energy: ½mv² = ½ × 2 × 144 = 144 J. The two methods agree, which confirms the result.
Traps that cost marks
- Mixing sign conventions in mirror and lens problems.
- Using g = 10 in one step and 9.8 in another without stating it.
- Treating vectors as scalars and dropping direction.
- Forgetting to convert units before substitution.
- Writing a numerical answer without the unit or with excessive significant figures.