Physics Formula Sheet: What to Memorise vs What to Derive for Classes 11-12

Physics in Classes 11 and 12 is often perceived as a massive exercise in rote memorisation. With hundreds of formulas spanning Mechanics, Electrodynamics, Optics, and Modern Physics, trying to commit every single equation to memory leads to severe cognitive overload during board exams, JEE, and NEET.

The secret to scoring high isn't remembering everything. It is about maintaining a strict boundary between core results you must memorise instantly and subsidiary formulas you must be able to derive in seconds.

Here is how to curate your physics formula sheet for the 2026-27 academic session.

The Core Memorisation List: Direct Application

Certain formulas appear repeatedly in numerical problems. Deriving these during an exam wastes precious minutes. You must commit these fundamental results to memory, along with their valid boundary conditions.

Mechanics

• Equation of motion under constant acceleration: $s = ut + \frac{1}{2}at^2$ and $v^2 = u^2 + 2as$
• Centripetal acceleration: $a_c = \frac{v^2}{r} = \omega^2 r$
• Time period of a simple pendulum: $T = 2\pi\sqrt{\frac{L}{g}}$
• Escape velocity: $v_e = \sqrt{\frac{2GM}{R}}$

Electrodynamics

• Coulomb’s Law: $F = \frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r^2}$
• Electric field due to a point charge: $E = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}$
• Ohm’s Law: $V = IR$
• Magnetic force on a moving charge: $\vec{F} = q(\vec{v} \times \vec{B})$
• RMS value of alternating current: $I_{rms} = \frac{I_0}{\sqrt{2}}$

Optics and Modern Physics

• Lensmaker's Formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$
• De Broglie wavelength: $\lambda = \frac{h}{p} = \frac{h}{mv}$
• Radioactive decay law: $N(t) = N_0 e^{-\lambda t}$

Memorising these allows you to jump straight into substitution and algebraic manipulation, which is critical for time management in both NEET and JEE Main.

The Derivation List: Never Memorise These

If you try to memorise specialized variations of standard formulas, your memory will fail under exam pressure. Instead, master the underlying principles so you can derive them in under 60 seconds.

| Concept to Derive | Starting Principle | Why You Shouldn't Memorise | | :--- | :--- | :--- | | Electric field of a dipole at axial/equatorial points | Coulomb's Law + Vector Superposition | Too many sign variations and distance powers ($r^3$ vs $r^2$) to keep straight. | | Torque on a current-carrying loop | $\vec{\tau} = \vec{m} \times \vec{B}$ or $\vec{r} \times \vec{F}$ | Easily reconstructed by drawing a rectangular loop in a uniform magnetic field. | | Impedance ($Z$) of an LCR series circuit | Phasor algebra or differential equations | Memorising final formulas for phase angle $\tan\phi$ leads to confusion with inductive/capacitive dominance. | | Velocity of efflux (Torricelli’s Law) | Bernoulli’s Principle | Deriving it from energy conservation takes three lines and ensures zero conceptual errors. |

When you practice numericals for board exams (CBSE, ICSE, or state boards), force yourself to write out the full derivation at least twice before using the shortcut result. This guarantees that if a 3-mark or 5-mark subjective question asks for the proof, you won't blank out.

Managing Approximations and Special Cases

Competitors in JEE Advanced and NEET often stumble by using general formulas where approximations apply. Your formula sheet should explicitly list the condition alongside the shortcut.

• Binomial Approximation: When $x \ll 1$, remember that $(1 + x)^n \approx 1 + nx$. This is heavily used in electrostatics (finding fields at large distances) and optics (interference fringe widths).
• Doppler Effect: Instead of memorising four separate formulas for approaching and receding sources/listeners, memorise the general master formula and use standard sign conventions: $f' = f \left( \frac{v \pm v_o}{v \mp v_s} \right)$

Quick Checklist for Your Final Formula Sheet

Before you finalise your study sheets for the upcoming tests, run them through this Edumath checklist:

• [ ] No Derivations on the Sheet: Only write final results, constants, and variable definitions. Proofs belong in your notebook, not your cheat sheet.
• [ ] Units and Dimensions Included: Next to complex formulas (like self-inductance or magnetic flux), note down the SI unit and dimensional formula.
• [ ] Conditionals Highlighted: Clearly mark when a formula is valid only for specific cases (e.g., constant acceleration, isothermal processes, or small angles).
• [ ] Vector vs Scalar: Use bold letters or arrow notations ($\vec{E}$, $V$) so you never miss a dot or cross product in vector-heavy chapters like Electrostatics and Magnetism.

Keep your formula sheet concise, update it weekly as you solve mock tests on Edumath, and rely on derivation for anything complex.