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

Physics is not a subject of rote memorisation, yet walking into a CBSE board exam or a JEE/NEET testing hall without memorised results is a recipe for running out of time. With the updated 2026-27 competency-based NCERT and NCF-SE frameworks, examiners test your conceptual application rather than your ability to plug numbers into blind equations.

To build an efficient physics formula sheet, you must divide your syllabus into two distinct categories: core results you must commit to memory, and foundational relations you must know how to derive on the spot.

The Memorisation Tier: High-Speed Tools

Certain formulas appear repeatedly across numerical problems. Deriving these from scratch every single time wastes critical minutes during an exam. These belong on your quick-reference formula sheet.

Mechanics

• Equations of motion under constant acceleration: $v = u + at, \quad s = ut + \frac{1}{2}at^2, \quad v^2 = u^2 + 2as$
• Centripetal acceleration and force: $a_c = \frac{v^2}{r} = \omega^2 r, \quad F_c = \frac{m v^2}{r}$
• Work-energy relations and potential energy profiles (Spring potential energy $U = \frac{1}{2}kx^2$).

Electrodynamics & Magnetism

• Coulomb's Law and Electric Field due to a point charge: $F = \frac{1}{4\pi\varepsilon_0}\frac{q_1 q_2}{r^2}, \quad E = \frac{1}{4\pi\varepsilon_0}\frac{q}{r^2}$
• Capacitance formulas for parallel plates (with and without dielectrics): $C = \frac{\varepsilon_0 A}{d}, \quad C' = \frac{K \varepsilon_0 A}{d}$
• Magnetic force on a moving charge and current-carrying wire: $\vec{F} = q(\vec{v} \times \vec{B}), \quad \vec{F} = I(\vec{L} \times \vec{B})$
• Resonance frequency in an $LCR$ series circuit: $\omega_0 = \frac{1}{\sqrt{LC}}$

Optics & Modern Physics

• Lens Maker's Formula and Thin Lens Formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right), \quad \frac{1}{f} = \frac{1}{v} - \frac{1}{u}$
• De Broglie wavelength: $\lambda = \frac{h}{p} = \frac{h}{\sqrt{2mE}}$

The Derivation Tier: Conceptual Anchors

Never memorise complex intermediate expressions or specific geometry-dependent formulas. Instead, memorise the foundational law or theorem, and practise the standard calculus or geometric steps to reach the final answer.

• Gauss's Law Applications: Do not memorise the electric field formula for an infinite sheet, cylinder, or spherical shell separately. Memorise Gauss's law ($\oint \vec{E} \cdot d\vec{A} = \frac{q_{\text{enclosed}}}{\varepsilon_0}$) and the symmetry arguments used to pull $E$ out of the integral.
• Ampere's Circuital Law Applications: Memorise $\oint \vec{B} \cdot d\vec{l} = \mu_0 I_{\text{enc}}$ to derive the magnetic field inside a toroid or solenoid.
• Motional Electromotive Force: Remember $e = -\frac{d\Phi_B}{dt}$ and Lorentz force dynamics rather than shortcut formulas for obscure conductor shapes.
• Simple Harmonic Motion Time Periods: For complex physical pendulums or U-tube liquid oscillations, rely on setting up the torque or force equation: $\tau = -I\alpha \implies \alpha + \omega^2 \theta = 0$.

Comparison: Memorise vs. Derive

| Topic | What to Memorise | What to Derive | | :--- | :--- | :--- | | Electrostatics | Coulomb’s law, point charge field, dipole field on axial/equatorial lines. | Electric field due to continuous charge distributions via integration. | | Current Electricity | Ohm's Law, drift velocity relation ($I = nAve$), Kirchhoff’s rules. | Equivalent resistance of complex infinite ladders or bridge networks. | | Wave Optics | Fringe width expression ($\beta = \frac{\lambda D}{d}$), condition for maxima/minima. | Intensity distribution derivation using phasor addition. | | Ray Optics | Snell's law, lens formula, prism deviation formula ($\delta = i_1 + i_2 - A$). | Exact ray tracing geometry for non-standard multi-surface systems. |

Quick Checklist for Edumath Students

• [ ] Limit your sheet size: A valid physics formula sheet for Classes 11-12 should fit on both sides of a single A4 sheet. If it spans three pages, you are memorising derivations instead of concepts.
• [ ] Include condition boundaries: Always write the validity conditions next to a formula (e.g., valid only for small angles $\theta$, or non-relativistic velocities).
• [ ] Define every variable: A symbol like $\rho$ can mean resistivity in current electricity, density in mechanics, or volume charge density in electrostatics. Always note context.
• [ ] Practise active recall: Do not read your formula sheet like a novel. Cover the right-hand column of results and derive them on rough paper weekly.