20 Most Important Formulas for CBSE Class 10 Board Exam

Analysing 10 years of CBSE Class 10 Board papers reveals a small set of formulas that show up almost every year. Master these 20 and you cover ~60% of the numerical marks.

Physics (7 formulas)

1. Ohm's Law — V = IR. Almost every year. Direct 3-mark numerical.
2. Power in a circuit — P = VI = I^2 R = V^2/R. Both direct and combined-circuit problems.
3. Heating effect — H = I^2 R t (Joule's law). Common in 3-mark numerical.
4. Mirror formula — 1/f = 1/v + 1/u with sign convention. Concave/convex mirror problems.
5. Lens formula — 1/f = 1/v - 1/u. Convex lens image formation.
6. Magnification (mirrors) — m = -v/u. Always paired with mirror formula.
7. Magnification (lenses) — m = v/u (note: no negative sign, opposite convention). Trap!

Chemistry (6 formulas)

1. Combination — A + B \to AB. Identify by pattern.
2. Decomposition — AB \to A + B.
3. Displacement — A + BC \to AC + B (uses reactivity series).
4. Double displacement — AB + CD \to AD + CB.
5. pH definition — pH = -\log[H^+]. Buffer/salt questions.
6. Combustion — \text{Fuel} + O_2 \to CO_2 + H_2O. Balance carefully.

Maths (7 formulas)

1. Quadratic formula — x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}. Direct application.
2. Discriminant — D = b^2 - 4ac. Nature of roots question.
3. Sum & product of roots — \alpha + \beta = -b/a, \alpha\beta = c/a.
4. AP nth term — a_n = a + (n-1)d.
5. AP sum — S_n = \frac{n}{2}[2a + (n-1)d].
6. Section formula — \left(\frac{mx_2 + nx_1}{m+n}, \frac{my_2 + ny_1}{m+n}\right).
7. Trig ratios — \sin, \cos, \tan for standard angles 0°, 30°, 45°, 60°, 90°.

How to use this list

• Week 1: memorise all 20 formulas + one worked example each.
• Week 2: attempt one PYQ (previous year question) per formula.
• Week 3: solve mixed problems that use 2–3 formulas together.

Every one of the above has a detailed page on Board Formulas with derivation, worked example, common mistakes and practice questions. Bookmark the ones you struggle with.

Mark distribution snapshot

Rough average per CBSE Class 10 board paper:

• Direct formula application: 15–20 marks
• Multi-formula numerical: 10 marks
• Derivation/definition: 5–8 marks

Master the 20 above and 30+ marks are within reach.