Units, Dimensions and Vectors
NIOS · Class 12 · Physics
Complete topic list for Units, Dimensions and Vectors in NIOS Class 12 Physics. Key concepts, sub-topics, and what to focus on for board exams.
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Physical World and Measurements
- Physics is the most fundamental science — it covers mechanics, heat, optics, electricity, magnetism, nuclear physics, and electronics.
- Physics ranges from the study of sub-atomic particles (size ~10⁻¹⁵ m) to the entire universe (size ~10²⁶ m).
- Every natural phenomenon requires measurement of physical quantities for complete study.
SI Units and Standards of Measurement
- The SI system (Système International d'Unités) was adopted at the 14th General Conference on Weights and Measures in 1971.
- There are 7 base SI units: metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), candela (cd), mole (mol).
- The SI system is a metric (decimal) system — larger and smaller units are multiples or submultiples of 10.
Significant Figures
- Significant figures are the digits in a measurement that are known with certainty plus the first uncertain digit.
- More significant figures = more accurate measurement = less percentage error.
- Rule 1: All non-zero digits are significant. (Example: 315.58 → 5 sig figs)
Dimensions of Physical Quantities
- Dimensions express a physical quantity in terms of fundamental quantities: Mass (M), Length (L), Time (T), Electric Current (I), Temperature (θ).
- In mechanics, all quantities can be expressed using just M, L, T.
- Volume: [L³], Density: [ML⁻³], Speed/Velocity: [LT⁻¹], Acceleration: [LT⁻²], Force: [MLT⁻²]
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