Physics: Mechanics, Heat, Waves and Electricity
Physics questions test conceptual understanding plus simple numerical application. The recurring topics are Newton's laws, motion equations, work-power-energy, pressure and density, heat and temperature, reflection and refraction, sound, and basic current electricity (Ohm's law, series and parallel circuits).
Concepts to hold firmly
- v = u + at, s = ut + ½at², v² = u² + 2as - valid only for uniform acceleration.
- F = ma; weight = mg; action and reaction act on different bodies.
- Work = force × displacement in the direction of force; power = work / time.
- Ohm's law V = IR; in series resistance adds and current is common; in parallel voltage is common and 1/R = 1/R₁ + 1/R₂.
- Light bends toward the normal entering a denser medium; the angle of incidence equals the angle of reflection.
Traps to expect
- Mass vs weight confusion (mass in kg is constant; weight in newtons varies with g).
- Zero work despite effort - if displacement is perpendicular to force, work is zero.
- Series vs parallel rules swapped.
- Heat vs temperature treated as synonyms.
Rule of thumb
Before calculating, write down the knowns with units and the unknown. If a quantity is not mentioned and not needed, do not invent it.
Worked example: Two 6 Ω resistors in parallel: 1/R = 1/6 + 1/6 = 1/3, so R = 3 Ω - less than either resistor, as parallel resistance always is.