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

Physics in Classes 11 and 12 often feels like an endless list of equations. When preparing for CBSE, ICSE, state boards, JEE Main, JEE Advanced, or NEET, trying to rote-learn every single expression is a recipe for disaster. Memory is a finite resource under exam pressure.

To score high, you need a strategy. You must categorise formulas into two distinct buckets: those you must instantly recall, and those you should be able to derive within seconds.

The Core Memorisation List: Direct Tools for Speed

Some formulas appear so frequently that stopping to derive them will cost you critical minutes in a timed exam like the JEE or NEET. These are your foundational tools. You must know them by heart, including their sign conventions and valid conditions.

Mechanics

• Equations of motion (constant acceleration): $v = u + at$, $s = ut + \frac{1}{2}at^2$, $v^2 = u^2 + 2as$.
• Centripetal acceleration: $a_c = \frac{v^2}{r} = \omega^2 r$.
• Time period of a simple pendulum: $T = 2\pi\sqrt{\frac{L}{g}}$.

Electrodynamics

• Coulomb’s Law: $F = \frac{1}{4\pi\varepsilon_0} \frac{q_1 q_2}{r^2}$.
• Ohm’s Law and Resistivity: $V = IR$ and $R = \rho \frac{l}{A}$.
• Magnetic force on a moving charge: $\vec{F} = q(\vec{v} \times \vec{B})$, or magnitude $F = qvB\sin\theta$.

Optics and Modern Physics

• Lens Maker’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 saves precious seconds during numerical problem-solving in board exams and competitive tests.

The Derivation List: Concepts to Build on the Spot

If you forget a complex formula, you can often reconstruct it if you know the fundamental law or calculus relation behind it. Deriving these during practice strengthens your conceptual clarity for NCF-SE competency-based questions.

| Concept / Topic | What to Remember Instead | How to Reconstruct Quickly | | :--- | :--- | :--- | | Work done by variable force | Definition of work | Integrate $dW = F \, dx$ between limits. | | Moment of Inertia (Standard bodies) | Parallel/Perpendicular Axis Theorems | Integrate $dI = r^2 dm$ for basic ring/rod, then shift axes. | | Electric field due to an infinite sheet | Gauss's Law ($\oint \vec{E} \cdot d\vec{A} = \frac{q_{\text{enclosed}}}{\varepsilon_0}$) | Apply Gaussian cylinder surface symmetry. | | Inductor energy storage | Faraday's Law and self-induction ($e = -L\frac{di}{dt}$) | Integrate power $P = eI$ over time. |

Never waste memory space on niche variations of these derivations. Understand the starting theorem, and the rest will follow.

Applying the Strategy to Exam Types

Different exams demand different balances between memory and derivation:

• CBSE, ICSE, and State Boards: Board examiners award step marks. Knowing how to start from first principles and derive expressions like the electric field on the axial line of a dipole is vital for 3-mark and 5-mark subjective questions.
• JEE Main and NEET: These tests require rapid calculation. While you rely heavily on the memorisation list, conceptual clarity helps you manipulate standard formulas for modified boundary conditions without panicking.
• JEE Advanced: Rote learning fails here entirely. Advanced questions often combine two distinct chapters (e.g., thermodynamics and electrostatics). Here, the ability to derive relationships from fundamental laws is your primary weapon.

Quick Checklist

Before you finalise your personal formula notebook for the 2026-27 academic session, run through this checklist:

• [ ] Do I know the vector form of the formula, not just the scalar magnitude?
• [ ] Am I clear about the SI units and dimensional formula of every term?
• [ ] Do I know the exact limitations (e.g., Is this valid only for small angles? Is it restricted to adiabatic processes?)?
• [ ] Can I derive this expression from a fundamental law in under 60 seconds?

Stop treating your formula sheet as a passive list to read before sleep. Treat it as an active construction site where memory meets logic.