Class 11 Physics Chapter 2 Notes : Unit and Measurement

The seven fundamental SI quantities are: length (metre), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela). All other physical quantities are derived from combinations of these seven base units.

Accuracy refers to how close a measured value is to the true value. Precision refers to how close repeated measurements are to each other, regardless of the true value. A measurement can be precise but inaccurate (consistently wrong in the same direction — systematic error) or accurate but imprecise (correct on average but scattered).

Percentage error = (Mean Absolute Error / Mean Value) × 100. First, calculate the mean of all readings. Then find the absolute error for each reading. Average those absolute errors to get the mean absolute error. Divide by the mean value and multiply by 100. This tells you the reliability of your measurement as a percentage.

Dimensional analysis is a method used to check the correctness of equations, derive relationships between physical quantities, and convert units from one system to another.

Significant figures help express the precision of measurements and prevent overestimating the accuracy of calculated results