Physics
Physics in the NPCIL Scientific Assistant exam tests mechanics, electricity and magnetism, waves, optics, heat, and modern physics, usually through short numericals and unit-based concepts. Questions often combine two ideas, such as a resistor network with power dissipation or a photoelectric cell with stopping potential.
Core rules
- SI units: force in newton, energy in joule, power in watt, pressure in pascal.
- Newton's second law F = ma; work-energy theorem W_net = ΔKE.
- Ohm's law V = IR; series resistances add, parallel conductances add.
- Wave relation v = fλ; for light in vacuum c ≈ 3×10^8 m/s.
- Mirror/lens formula 1/f = 1/v − 1/u with the Cartesian sign convention.
- Photoelectric equation hf = φ + KE_max; radioactive decay N = N0 e^(−λt).
Worked example. A 2 kg block starts from rest and slides 5 m down a frictionless 30° incline. Height fallen h = 5 sin 30° = 2.5 m. By energy conservation, ½mv² = mgh, so v = √(2gh) = √(2×9.8×2.5) = √49 = 7 m/s. The mass cancels, so the answer does not depend on 2 kg.
Traps. Use g = 9.8 m/s² unless told 10; convert cm and g to SI; in lens problems, object distance is negative under the Cartesian convention; RMS values are not peak values; radioactive half-life is not linear.