Physics and Chemistry - CBT 2
What the domain tests
CBT 2 physics and chemistry go deeper than CBT 1: units and measurement, kinematics and laws of motion, work-power-energy, gravitation, mechanical properties of matter, heat and thermodynamics, waves and optics, electrostatics, current electricity, magnetism, and modern physics basics. Chemistry covers atomic structure, periodicity, chemical bonding, mole concept, acids-bases-salts, electrochemistry, metals and non-metals, hydrocarbons and polymers.
Core rules
- Equations of motion: v = u + at, s = ut + ½at², v² = u² + 2as - valid only for uniform acceleration.
- Ohm's law V = IR; series resistances add, parallel ones give 1/R = 1/R₁ + 1/R₂ + …
- Mirror/lens formula 1/v − 1/u = 1/f (Cartesian signs); power of a lens in dioptres = 1/f in metres.
- Mole concept: 1 mole = 6.022 × 10²³ particles; molar volume of a gas at STP = 22.4 L.
- Periodic trend: atomic radius decreases across a period, increases down a group; electronegativity does the opposite.
Worked example
Three resistors of 2 Ω, 3 Ω and 6 Ω are joined in parallel. Then 1/R = 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1, so R = 1 Ω. Note the result is smaller than the smallest resistor - a useful sanity check for every parallel calculation.
Traps that cost marks
Applying kinematic equations when acceleration is not uniform. Using the wrong sign convention in mirror and lens problems: distances measured against the incident light are negative. Forgetting that parallel resistance is always less than the least branch, and that 1 mole of a gas occupies 22.4 L only at STP, not at room conditions.