Physics and Chemistry
The Physics and Chemistry section tests school-level concepts with numerical emphasis: motion, force, work and energy, electricity, optics, heat, atomic structure, periodic trends, acids and bases, metals and fuels. Questions are usually direct, so formula recall and unit discipline matter.
Core rules and concepts
- Motion: v = u + at, s = ut + ½at², v² = u² + 2as. Work = force × displacement; power = work/time; 1 kWh = 3.6×10⁶ J.
- Electricity: Ohm's law V = IR. In series, current is common and resistances add; in parallel, voltage is common and 1/R = 1/R₁ + 1/R₂.
- Optics: mirror formula 1/f = 1/v + 1/u; lens formula 1/f = 1/v − 1/u; use sign conventions consistently.
- Chemistry: atomic number = protons; mass number = protons + neutrons. Across a period, atomic radius decreases and electronegativity increases. pH < 7 is acidic; each unit is a tenfold change in H⁺ concentration.
- Acids react with bases to form salt and water; metals above hydrogen in the reactivity series displace it from dilute acids.
Worked example
A 6 Ω and a 3 Ω resistor are in parallel, and this combination is in series with 4 Ω across 12 V. Parallel resistance = (6×3)/(6+3) = 2 Ω. Total = 2 + 4 = 6 Ω. Current = 12/6 = 2 A. The 4 Ω resistor drops 8 V, leaving 4 V across the parallel pair.
Traps
Using g for G, writing kWh as kW, adding parallel resistances directly, ignoring sign convention in optics, and confusing molarity with molality.