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Cheat sheet · Class 11 · CBSE · Science Physics

Units and Measurements cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 11 · Physics

Cheat sheet

Chapter 1Units and Measurements

Seven base units: m, kg, s, A, K, mol, cd — “My Kid Sings And Keeps Many Candles”.

1. SI Base Units

QuantityUnit
Lengthmetre (m)
Masskilogram (kg)
Timesecond (s)
Electric currentampere (A)
Temperaturekelvin (K)
Amount of substancemole (mol)
Luminous intensitycandela (cd)

Supplementary: plane angle — radian (rad); solid angle — steradian (sr).

2. Significant Figures

  • All non-zero digits are significant.
  • Zeros between non-zero digits are significant (2.005 → 4).
  • Leading zeros are not significant (0.0042 → 2).
  • Trailing zeros after a decimal point are significant (4.600 → 4).

Rounding in calculations

× and ÷: result keeps the least number of significant figures. + and −: result keeps the least number of decimal places.

3. Dimensional Analysis

[F]=[MLT−2][F] = [MLT^{-2}][E]=[ML2T−2][E] = [ML^2T^{-2}][P]=[ML2T−3][P] = [ML^2T^{-3}]
[p]=[MLT−1][p] = [MLT^{-1}][Pressure]=[ML−1T−2][\text{Pressure}] = [ML^{-1}T^{-2}][G]=[M−1L3T−2][G] = [M^{-1}L^3T^{-2}]

Check equations

Each term of a correct equation has the same dimensions (principle of homogeneity).

Derive relations

e.g. period of a pendulum T∝l/gT \propto \sqrt{l/g}.

Limits

Cannot find dimensionless constants or handle sums of terms / trig, log, exp functions.

4. Key Points to Remember

  • Dimensionless: angle, strain, refractive index, relative density.
  • Same dimensions: work, energy, torque.
  • 1 light year ≈ 9.46 × 10¹⁵ m; 1 AU ≈ 1.5 × 10¹¹ m.
  • Parsec ≈ 3.08 × 10¹⁶ m.
  • A dimensionally correct equation need not be physically correct.
  • Exact numbers (like 2 in 2πr) have infinite significant figures.

Remember: Base units | Significant figures rules | [MLT] dimensions

Units and Measurements: questions and notes

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