Physics: Principles, Units and Fast Recognition
Physics in MHT-CET rewards fast, clean application of Class 11–12 Maharashtra State Board concepts: rotational dynamics, gravitation, SHM, thermodynamics, wave optics, electrostatics, current electricity, magnetism, modern physics and semiconductors. Questions are single-correct MCQs, so the winning skill is recognising the principle in a few seconds and avoiding unit slips.
Core rules that decide marks
- Rotational motion: τ = Iα about a fixed axis; rolling without slipping links v = ωR and a = αR. Use the parallel-axis theorem I = I_cm + Md².
- SHM: a = −ω²x; v_max = ωA; T = 2π√(m/k) for a spring and 2π√(l/g) for a simple pendulum.
- Optics: path difference Δ = nλ for constructive and (2n−1)λ/2 for destructive interference; fringe width β = λD/d.
- Electricity: series resistors add, parallel conductances add; drift velocity is small even though the signal is fast.
Worked example
A particle executes SHM with amplitude 5.0 cm and period 0.20 s. Find its maximum speed. ω = 2π/T = 2π/0.20 = 31.4 rad/s. Convert A = 5.0 cm = 0.050 m. v_max = ωA = 31.4 × 0.050 = 1.57 m/s.
Traps that cost marks
- Mixing cm and m; this is the commonest error in SHM and optics.
- Using g = 10 m/s² when the paper expects 9.8, or vice versa.
- Confusing rms and peak values in AC.
- Forgetting that a rolling body's total KE = ½mv² + ½Iω².