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Questions and Answers
What is a unit in the context of measurement?
What is a unit in the context of measurement?
A unit is a certain basic, arbitrarily chosen, internationally accepted reference standard.
Which of the following systems was previously used for measurement? (Select all that apply)
Which of the following systems was previously used for measurement? (Select all that apply)
What units are used for length, mass, and time in the SI system?
What units are used for length, mass, and time in the SI system?
The SI system includes only seven base units.
The SI system includes only seven base units.
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What is the unit for plane angle in the SI system?
What is the unit for plane angle in the SI system?
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What is the unit for solid angle in the SI system?
What is the unit for solid angle in the SI system?
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In the CGS system, the base unit for mass is the ______.
In the CGS system, the base unit for mass is the ______.
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What does SI stand for?
What does SI stand for?
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Study Notes
Introduction to Measurement
- Measurement involves comparing a physical quantity to a reference standard called a unit.
- Measurement results are expressed as a number and a unit.
- All physical quantities can be related to a limited set of fundamental or base units.
- Units derived from base units are called derived units.
- A complete set of base and derived units forms a system of units.
The International System of Units (SI)
- The SI is the internationally accepted system of units.
- Developed and recommended by the General Conference on Weights and Measures in 1971.
- Utilizes decimal system for simple and convenient conversions.
- SI uses seven base units for fundamental quantities.
SI Base Units
- Length: meter (m) defined as the distance travelled by light in vacuum in 1/299,792,458 of a second (1983).
- Mass: kilogram (kg) defined as the mass of the international prototype of the kilogram (a platinum-iridium alloy cylinder).
- Time: second (s) defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-133 atom.
- Electric Current: ampere (A) defined as the constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10−7 newton per metre of length.
- Thermodynamic Temperature: kelvin (K) defined as 1/273.16 of the thermodynamic temperature of the triple point of water.
- Amount of Substance: mole (mol) defined as the amount of substance that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.
- Luminous Intensity: candela (cd) defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.
Additional SI Units
- Plane Angle: radian (rad) defined as the ratio of the length of an arc to the radius of the circle.
- Solid Angle: steradian (sr) defined as the ratio of the intercepted area of a spherical surface to the square of its radius.
Previous Systems of Units
- CGS (centimeter-gram-second)
- FPS (foot-pound-second)
- MKS (meter-kilogram-second)
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Description
This quiz covers the fundamentals of measurement, including the definition of base and derived units. Explore the International System of Units (SI) and learn about its seven base units and their definitions. Test your knowledge on measurement concepts and SI standards.
