ELECTROMAGNETIC SPECTRUM (increasing frequency / decreasing wavelength):
  Radio waves: >1mm | Microwaves: 1mm-10⁻³mm | Infrared: 10⁻³mm-700nm
  Visible: 400-700nm (VIBGYOR) | Ultraviolet: 400nm-1nm
  X-rays: 1nm-10⁻³nm | Gamma rays: <10⁻³nm

USES:
  Radio: communication | Microwave: radar, microwave oven, satellite
  IR: TV remote, night vision, heat | UV: sterilization, vitamin D, security marking
  X-ray: medical imaging, luggage scanning | Gamma: cancer treatment, food irradiation

All EM waves travel at c = 3×10⁸ m/s in vacuum
Transverse waves | do not require medium | carry energy and momentum

RAY OPTICS — MIRRORS:
  Mirror formula: 1/v + 1/u = 1/f (note: different from lens formula sign)
  Focal length: f = R/2
  Magnification: m = -v/u (negative means inverted)
  
  Concave mirror (f negative): converging, real inverted image when u > f
  Convex mirror (f positive): diverging, always virtual erect diminished image

SIMPLE HARMONIC MOTION:
  x = A sin(ωt + φ) | velocity: v = Aω cos(ωt)
  Acceleration: a = -ω²x (proportional to displacement, opposite direction)
  
  Time period:
    Spring-mass: T = 2π√(m/k)
    Simple pendulum: T = 2π√(L/g) — independent of mass and amplitude
    Liquid in U-tube: T = 2π√(L/2g) where L = total length
  
  Energy in SHM:
    KE = ½mω²(A²-x²) | PE = ½mω²x² | Total = ½mω²A² (constant)
    KE maximum at x=0 (equilibrium) | PE maximum at x=±A (extremes)

WAVES:
  Wave equation: v = fλ | for string: v = √(T/μ)
  
  Standing waves — string both ends fixed:
    Harmonics: fn = nv/2L | fundamental = v/2L
    Nodes (no displacement) | Antinodes (maximum displacement)
  
  Sound:
    Intensity: I ∝ A² | Loudness (dB): β = 10 log(I/I₀) where I₀ = 10⁻¹² W/m²
    Beats: n_beats = |f₁ - f₂| (per second)
    Doppler: f' = f × (v ± v_observer)/(v ∓ v_source)

SECTION APPROACH:
  Attempt: Modern Physics (easiest for formula application) first
  Then: Optics, Current Electricity (systematic solving)
  Then: Mechanics (time-consuming, do last)
  Skip: Extremely calculation-heavy problems — check with 1-2 options first

ACCURACY OVER SPEED:
  NEET Physics: better to do 35/45 with 90% accuracy
  Than attempt all 45 with 70% accuracy (negative marking hurts)
  
  Wrong answer: -1 mark | Correct: +4 marks
  Break-even: 1 correct compensates for 4 wrong (4-4=0)
  Strategy: skip if less than 60% confident

FORMULA SHEET PREPARATION:
  Make a 2-page formula sheet by chapter
  Revise formula sheet daily last 30 days before exam
  Do 10-15 PYQ per chapter after each revision