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, or NEET, students make a critical error: they try to memorise every single formula in NCERT. This leads to cognitive overload, confusion in exam halls, and poor problem-solving skills.

A smart student maintains a lean formula sheet. To build one for the 2026-27 academic session, you must categorize every equation into two buckets: foundational results to memorise, and intermediate steps to derive.

The Core Problem with Rote Memorisation

Indian competitive and board exams test application, not recall. If you memorise $v = u + at$, $s = ut + \frac{1}{2}at^2$, and $v^2 = u^2 + 2as$ as three isolated facts, your brain stores three separate blocks of data.

If you instead memorise the definition of acceleration $a = \frac{dv}{dt}$ and velocity $v = \frac{ds}{dt}$, the kinematic equations take seconds to derive via calculus. More importantly, when an examiner twists a standard problem—such as acceleration varying with time—rote memorisation fails completely, whereas derivation skills succeed.

What You Must Memorise (The Anchor Formulas)

Anchor formulas are fundamental laws, definitions, or experimental results that cannot be derived within the scope of your syllabus. These must be locked into your long-term memory.

• Mechanics: Newton's Second Law ($\vec{F} = \frac{d\vec{p}}{dt}$), Universal Law of Gravitation ($F = \frac{GM_1M_2}{r^2}$), and Hooke's Law ($F = -kx$).
• Electrodynamics: Coulomb's Law ($F = \frac{1}{4\pi\varepsilon_0}\frac{q_1q_2}{r^2}$), Lorentz Force ($\vec{F} = q(\vec{E} + \vec{v}\times\vec{B})$), and Faraday's Law ($\mathcal{E} = -\frac{d\Phi_B}{dt}$).
• Optics: Snell's Law ($n_1\sin i = n_2\sin r$ and the Lens Maker's Formula structure).
• Modern Physics: Einstein's Photoelectric Equation ($K_{\max} = h\nu - \phi$).

These anchors act as starting points for derivations during an exam.

What You Should Derive (The Derived Results)

Derived formulas are logical extensions of anchor formulas. You should practice these derivations until you can reproduce them in under 60 seconds. This ensures you never panic if you forget the final expression.

| Topic | Derived Result | Starting Anchor Formula | | :--- | :--- | :--- | | Rotational Motion | Moment of Inertia of a uniform rod about its center ($I = \frac{1}{12}ML^2$) | Definition of Moment of Inertia ($I = \sum m_ir_i^2$ or $\int r^2 dm$) | | Electrostatics | Electric field due to an infinite line charge ($E = \frac{\lambda}{2\pi\varepsilon_0 r}$) | Gauss's Law ($\oint \vec{E} \cdot d\vec{A} = \frac{q_{\text{enclosed}}}{\varepsilon_0}$) | | Current Electricity | Drift velocity relation ($I = nAv_d$) | Current definition ($I = \frac{dq}{dt}$) and microscopic motion | | Wave Optics | Fringe width in Young's Double Slit Experiment ($\beta = \frac{\lambda D}{d}$) | Path difference geometry for constructive interference |

When you know that $\beta = \frac{\lambda D}{d}$ comes from subtracting path lengths of light rays from two slits, you don't need to commit the formula to memory. You recreate it mentally.

Exam-Specific Strategy: Board Exams vs JEE/NEET

Your approach to formulas must adapt slightly depending on your target exam for the 2026-27 cycle.

For CBSE, ICSE, and State Boards

Board examiners award step marks. If you forget a complex formula like the velocity of efflux (Torricelli's Law), writing Bernoulli's equation ($\frac{P}{\rho} + gh + \frac{1}{2}v^2 = \text{constant}$) and substituting values will secure most of your marks. Always show the primary formula before plugging in numbers.

For JEE Main, Advanced, and NEET

Time is your primary constraint. You cannot afford to derive standard results like the time period of a physical pendulum or the magnetic field at the center of a circular arc during a computer-based test. For competitive exams, derive the result once during your study phase, then add the final expression directly to your high-yield formula sheet for rapid recall.

Quick Checklist

Use this quick checklist to audit your physics notebook today:

• [ ] Have I separated fundamental laws from derived formulas?
• [ ] Can I derive every standard result in Class 11 Mechanics using calculus?
• [ ] Is every formula on my sheet accompanied by the conditions/limitations of its use (e.g., valid only for small angles, or uniform electric fields)?
• [ ] Am I practicing numerical problems using the anchor formulas rather than jumping straight to shortcuts?