REAP tricks & mnemonics — save minutes on exam day
Subject-wise short tricks and memory hacks for Rajasthan Engineering Admission Process (REAP). Each one is meant to be used in the exam hall — read it, then lock it in with a quick practice question.
RLC Series Resonance: "VCL Zero" — At resonance, V_L = V_C exactly cancel, so impedance Z = R (minimum), current maximum. Resonant frequency: ω₀ = 1/√(LC). Remember "LC product under root inverted."
Photoelectric Effect: "FIKE" (Frequency, Intensity, KE) — Frequency controls max KE (E = hν - φ); Intensity controls current (number of electrons). Stopping potential: eV₀ = KE_max. More light = more electrons, NOT faster electrons.
Capacitor Series/Parallel: "Opposite of Resistors" — Series capacitors: 1/C_total = 1/C₁ + 1/C₂ (reciprocals add, like parallel resistors). Parallel: C_total = C₁ + C₂ (direct sum, like series resistors). Just flip the resistor rules.
Nuclear Decay: "Alpha drops 2/4, Beta no mass" — Alpha decay: Z-2, A-4 (loses 2He⁴). Beta⁻: Z+1, A same (neutron→proton). Beta⁺: Z-1, A same. Gamma: no Z/A change, only energy release.
Lenz Law Direction: "Nature Opposes" — Induced current's magnetic field always opposes the flux change causing it. Magnet approaching? Coil repels it. Magnet leaving? Coil attracts it. Fleming's right-hand rule for current direction.
EM Wave Frequency Order: "RMIVUXG" — Radio, Microwave, Infrared, Visible, Ultraviolet, X-ray, Gamma. Increasing frequency/energy, decreasing wavelength. Remember: c = νλ always, in vacuum c = 3×10⁸ m/s.
Chemistry
Alcohol Oxidation: "Primary-2, Secondary-1, Tertiary-0" — 1° alcohol → aldehyde → carboxylic acid (with strong oxidant). 2° alcohol → ketone (stops). 3° alcohol → no oxidation (no H on C-OH carbon). Lucas test: 3°>2°>1° reactivity.
Atomic Quantum Numbers: "SPDF" = 0,1,2,3 — Azimuthal quantum number l: s=0, p=1, d=2, f=3. Orbitals in subshell = 2l+1. Max electrons = 2(2l+1). Pauli: no two electrons with identical four quantum numbers.
d-Block Oxidation States: "Manganese Maximum +7" — Mn shows +2 to +7 (max in group). Scandium shows only +3. First-row d-block: variable oxidation due to close 3d/4s energies. Colored due to d-d transitions (partially filled d-orbitals).
AI-curated from widely-used exam techniques — always sanity-check a trick on a practice question before relying on it in the hall.
Tricks stick when you USE them
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Coordination Isomerism: "LIGPS" — Linkage (ambidentate like NO₂/ONO), Ionization (counter-ion exchange), Geometrical (cis/trans), Polymerization (different molecular formulas), Solvate (aqua vs solvent). Square planar/octahedral show geometrical isomerism.
Mathematics
Maxima/Minima: "First Zero, Second Decides" — Set f'(x)=0 for critical points. Then f''(x): positive→local minimum, negative→local maximum, zero→inconclusive (check higher derivatives). For intervals, check endpoints too.
Integration by Parts: "ILATE Priority" — Choose u by ILATE: Inverse trig, Logarithmic, Algebraic, Trigonometric, Exponential (decreasing priority). Formula: ∫u dv = uv - ∫v du. Lower priority becomes dv for easier integration.
Binomial Middle Term: "n Even=One, n Odd=Two" — If n even: middle term = (n/2 + 1)th term only. If n odd: two middle terms = (n+1)/2 th and (n+3)/2 th. Max coefficient always at middle term(s).
Conic Eccentricity: "CEPE" = 0,<1,1,>1 — Circle e=0, Ellipse e<1, Parabola e=1, Hyperbola e>1. Remember: b²=a²(1-e²) for ellipse; b²=a²(e²-1) for hyperbola. Focus-directrix ratio defines e.
Differential Equations Order/Degree: "Highest Derivative Power" — Order = highest derivative present (dy/dx is 1st, d²y/dx² is 2nd). Degree = power of highest-order derivative after removing radicals/fractions. Linear DE: degree=1 throughout.
Determinant Properties: "Row Ops Keep It Simple" — Swapping two rows: determinant changes sign. Row × k: determinant × k. Adding k×(another row) to a row: determinant unchanged. Two identical/proportional rows: det=0. Upper/lower triangular: det=product of diagonal.