Units and Measurements 11 Physics — Revision Notes
Physics is based on precise measurements of physical quantities. Understanding units and measurement systems is fundamental to studying physics and conduct
TL;DR: Physics is based on precise measurements of physical quantities. Understanding units and measurement systems is fundamental to studying physics and co…
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Physics is based on precise measurements of physical quantities. Understanding units and measurement systems is fundamental to studying physics and conduct
Physical Quantities and Units
- Physical quantity is anything that can be measured
- Fundamental quantities: length, mass, time, temperature, electric current
- Derived quantities obtained from fundamental quantities through mathematical relations
- Unit is a standard amount chosen to measure a physical quantity
- SI system is internationally used standard system of units
SI System of Units
- SI unit of length is meter (m)
- SI unit of mass is kilogram (kg)
- SI unit of time is second (s)
- SI unit of temperature is Kelvin (K)
- SI unit of electric current is ampere (A)
- SI unit of luminous intensity is candela (cd)
- SI unit of amount of substance is mole (mol)
Dimensions of Physical Quantities
- Dimension shows how a physical quantity depends on fundamental quantities
- Dimensions are represented using symbols: L for length, M for mass, T for time
- Dimensional analysis checks if an equation is dimensionally correct
- Dimension does not include numerical constant or angles
- Velocity has dimension LT to power negative 1
Measurement and Errors
- All measurements have some error due to instrument limitations
- Systematic error arises from faulty instrument or technique
- Random error arises from unpredictable fluctuations
- Absolute error is difference between measured and true value
- Relative error is absolute error divided by true value
Significant Figures
- Significant figures are reliable digits in a measurement
- All non-zero digits are significant
- Zeros between non-zero digits are significant
- Leading zeros are not significant
- Trailing zeros after decimal point are significant
Key Terms
- Physical Quantity: Measurable property that can be expressed as number and unit
- SI Unit: Internationally agreed standard unit for measuring physical quantities
- Dimension: Expression of physical quantity in terms of fundamental quantities
- Significant Figures: Reliable and meaningful digits in a measured or calculated value
Frequently Asked Questions
What is the difference between precision and accuracy?
Accuracy is how close a measurement is to the true value. Precision is how close repeated measurements are to each other. A measurement can be precise but not accurate.
How many significant figures are in 0.00450?
The number 0.00450 has three significant figures: 4, 5, and 0. Leading zeros are not significant, but the trailing zero after 5 is significant because it comes after the decimal point.
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