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Questions and Answers
Which of the following is a base unit for mass in the MKS system?
The SI system was developed by the International Bureau of Weights and Measures in 1971.
True
What is the length base unit in the CGS system?
Centimetre
The system that is currently internationally accepted for measurement is called the ______.
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Match the following systems of units with their respective base units for length:
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What are fundamental or base units used for?
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The International System of Units eliminates the need for different systems of units among countries.
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What are the units for expressing quantities obtained from combinations of base units called?
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The complete set of units, including both base and derived units, is known as the _____ of units.
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Match the following systems of units with their descriptions:
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Study Notes
Introduction to Units and Measurement
- Measurement involves comparing a physical quantity to a basic reference standard known as a unit.
- The outcome of a measurement is represented by a number and a corresponding unit.
- A limited number of units can express a wide range of physical quantities due to their interrelation.
The International System of Units (SI)
- Historically, different countries utilized varied systems for measurement, including CGS, FPS, and MKS systems.
- SI is the current internationally accepted measurement system, developed by BIPM and revised in November 2018.
- SI simplifies conversions within the system as it is based on a decimal framework.
SI Base Quantities and Units
- The seven base SI units defined include:
- Length: metre (m), based on the speed of light.
- Mass: kilogram (kg), defined by the Planck constant.
- Time: second (s), defined by atomic frequency.
- Luminous Intensity: candela (cd), defined by the luminous efficacy of radiation.
- Additional units for plane angles (radian, rad) and solid angles (steradian, sr) are treated as dimensionless.
Derived Units
- Units derived from the base units are termed derived units, essential for expressing various physical quantities.
- Derived units may have special names (e.g., Newton for force, Joule for energy).
Significance of Significant Figures
- Significant figures indicate the precision of a measurement, with reliable digits being certain and the last digit being uncertain.
- Each measurement report should convey its precision accurately, avoiding misleading implications through superfluous digits.
- For example, in the measurement of 1.62 s, the first two digits are significant, while the last digit reflects uncertainty, totaling three significant figures.
- Conversions between units do not alter the significant figures of a measurement.
General Guidelines on Measurement
- The accuracy of measurements can improve with technological advancements, leading to revised definitions of base units.
- Common SI prefixes for multiples and sub-multiples facilitate understanding of quantity magnitudes.
- Understanding significant figures is crucial for communicating measurement precision clearly.
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Description
This quiz covers the fundamentals of units and measurement in physics, including the definition of physical quantities and the reference standards used in measurement. Understand the concepts introduced in Chapter One to excel in this essential aspect of physics.
