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

Physics is notorious for its sheer volume of formulas. By the time you reach Class 12, you are juggling hundreds of equations across mechanics, electrodynamics, optics, and modern physics. Walk into a JEE or NEET hall, or even a CBSE/ICSE board exam, trying to memorise every single identity, and your brain will hit a bottleneck.

Smart preparation for the 2026-27 academic session requires a clear filter: what goes into your permanent memory, and what stays in your derivation toolkit.

The Core Problem with Rote Memorisation

Many students treat Physics like Chemistry—trying to memorise every sub-formula and special case. This approach fails for two reasons. First, competitive exams like JEE Main and Advanced test conceptual application, not plug-and-chug formula matching. Second, under exam stress, memorised formulas easily fade or get mixed up (e.g., confusing the time period of a spring-mass system with a simple pendulum).

When you understand the root derivation, you don't need to panic if you blank out. You can recreate the formula in 30 seconds.

Tier 1: Formulas You Must Memorise Instantly

These are your bedrock equations. You should know them so well that you can write them down without thinking. They are fundamental definitions or empirical laws that cannot be derived from first principles within the scope of your syllabus.

• Kinematics Core Equations: The standard motion equations under uniform acceleration, such as $v = u + at$ and $s = ut + \frac{1}{2}at^2$.
• Newton's Second Law & Friction: $\vec{F} = \frac{d\vec{p}}{dt}$ and $f_s \le \mu_N N$.
• Electrostatic Force & Field: Coulomb’s Law, $\vec{F} = \frac{1}{4\pi\varepsilon_0} \frac{q_1 q_2}{r^2}\hat{r}$, and the definition of electric field $\vec{E} = \frac{\vec{F}}{q_0}$.
• Magnetic Force: The Lorentz force equation, $\vec{F} = q(\vec{E} + \vec{v} \times \vec{B})$.
• Planck’s Energy Relation: $E = h\nu$ for modern physics.

These act as your axiomatic truths. Every complex problem starts by invoking one of these foundational pillars.

Tier 2: Results You Must Know by Heart (Standard Shortcuts)

These are derived formulas that appear so frequently in numerical problems that taking the time to derive them during an exam wastes precious minutes. Memorise the final result, but make sure you understand the boundary conditions under which they apply.

| Topic | Formula / Result | When to Use Directly | | :--- | :--- | :--- | | Rotational Motion | Moment of inertia of a solid cylinder about its central axis: $I = \frac{1}{2}MR^2$ | Direct substitution in rotational dynamics problems. | | Current Electricity | Drift velocity relation: $I = nAv_d$ | Connecting microscopic charge carriers to macroscopic current. | | Ray Optics | Lens Maker’s Formula: $\frac{1}{f} = (\mu - 1)\left(\frac{1}{R_1} - \frac{1}{R_2}\right)$ | Quick focal length calculations for custom lenses. | | SHM | Time period of a simple pendulum: $T = 2\pi\sqrt{\frac{L}{g}}$ | Rapid analysis of oscillation frequency changes. |

If you encounter these in a standard problem, plug in the values directly. However, if a problem introduces a non-standard geometry or variable mass, you must fall back on Tier 3.

Tier 3: Formulas to Derive (Never Memorise)

If you find yourself trying to memorise the formula for the electric field due to a finite charged rod at an arbitrary point, stop immediately. These are derived results that require calculus or symmetry arguments. Memorising them is a waste of cognitive space because examiners will often tweak the parameters anyway.

• Electric field of a continuous charge distribution: (Rings, infinite sheets, hollow/solid spheres). Memorise the method (using Gauss's Law or direct integration), not the final algebraic expression.
• Magnetic field due to a finite wire: Rely on the Biot-Savart Law application: $B = \frac{\mu_0 I}{4\pi r} (\sin\theta_1 + \sin\theta_2)$ Instead of memorising this with sign-convention confusion, draw the diagram and integrate or use geometry on the spot.
• Work done in isothermal and adiabatic processes: Know the starting point ($PV = \text{constant}$ or $PV^\gamma = \text{constant}$) and integrate $PdV$.

By focusing on how these formulas are built, you build the flexibility needed for high-level JEE and board analytical questions.

Quick Checklist for Your Formula Sheet

As you curate your personal formula sheets for Class 11 and 12 physics, run every entry through this filter:

• [ ] Is this a fundamental law (Tier 1)? $\rightarrow$ Memorise.
• [ ] Is this a standard result used in >50% of related problems (Tier 2)? $\rightarrow$ Memorise with conditions.
• [ ] Does this involve integration, specific geometries, or lengthy calculus (Tier 3)? $\rightarrow$ Practise the derivation weekly; do not memorise.
• [ ] Do I know the SI units and dimensional formula for every variable in this equation? $\rightarrow$ Mandatory for all tiers.

Keep your formula sheets concise. Edumath recommends updating your sheets after every chapter test so that by the time board exams and entrance tests arrive, your revision material is razor-sharp and tailored entirely to your weak spots.