Physics (Mechanics, Electricity and Magnetism, Optics, Modern Physics)
What this domain tests
Physics tests conceptual understanding and numerical application in mechanics, electricity and magnetism, optics and modern physics. Expect formula-based questions on motion, force, energy, circuits, lenses, photoelectric effect and atomic models.
Core rules
- Mechanics: F = ma; work-energy theorem; momentum conservation; projectile range R = u² sin 2θ / g.
- Electricity: V = IR; series resistance adds; parallel resistance follows 1/R = 1/R₁ + 1/R₂; power P = VI = I²R.
- Magnetism: force on a current-carrying conductor F = BIL sin θ; Fleming’s left-hand rule gives direction.
- Optics: 1/f = 1/v − 1/u with the Cartesian sign convention; magnification m = v/u.
- Modern physics: photoelectric equation E = hf − φ; de Broglie wavelength λ = h/p.
Worked example
A 6 Ω and a 3 Ω resistor are in parallel, and this combination is in series with 4 Ω across a 12 V supply. Parallel resistance = (6 × 3)/(6 + 3) = 2 Ω. Total resistance = 2 + 4 = 6 Ω. Current = 12/6 = 2 A. Voltage across the parallel pair = 2 × 2 = 4 V; branch currents are 4/6 A and 4/3 A, summing to 2 A.
Traps
Do not add parallel resistances directly. In lens problems, a sign error changes the answer; keep object distance negative under the usual convention. Distinguish mass from weight and r from R. In photoelectric questions, intensity changes current, while frequency changes stopping potential.
Exam focus
Write units beside every substitution and check whether the question asks for magnitude or direction.