Physics: Mechanics, Electricity, Optics and Modern Physics
Physics on KUUMAT samples the NEB 10+2 syllabus: mechanics, heat, waves and optics, electricity and magnetism, and modern physics. Items are usually short numericals or conceptual checks, so the mark comes from choosing the right principle and handling units, signs, and vector directions cleanly.
Core rules
- Convert to SI first: cm→m, g→kg, eV→J (1 eV = 1.60×10⁻¹⁹ J). Use g = 9.8 m/s² unless the paper states otherwise.
- Newton’s second law is ΣF = ma per axis. On a frictionless incline, weight resolves into mg sinθ along the plane and mg cosθ perpendicular to it.
- Resistors: series R = R₁+R₂+…; parallel 1/R = 1/R₁+1/R₂+…. Kirchhoff’s rules handle multi-loop circuits.
- Mirror/lens: 1/f = 1/v − 1/u with Cartesian signs; power P = 1/f (dioptre).
- Photoelectric effect: K_max = hf − φ, and stopping potential gives K_max = eV_s.
Worked example
A 2 kg block slides down a 30° frictionless incline. Along the plane, F = mg sin30° = 2×9.8×0.5 = 9.8 N, so a = F/m = 4.9 m/s². The normal force is mg cos30° ≈ 17.0 N, not mg.
Traps
- Mixing degrees and radians, or using g = 10 when options assume 9.8.
- Assuming tension is unchanged across a massive pulley.
- Sign errors in lens/mirror problems and in work done by or on a gas.
- Treating static friction as always μN; it only reaches μN at impending motion.