24 Questions
What is the unit for plane angle?
Radian
What is the unit for solid angle?
Steradian
Which of the following units are dimensionless quantities?
Radian and Steradian
What is the definition of the metre in terms of?
Speed of light in vacuum
What is the definition of the kilogram in terms of?
Planck constant
What is the definition of the second in terms of?
Caesium frequency
What is the unit of the speed of light in vacuum?
m/s
What is the term used to describe the units of physical quantities that are derived from the base units?
Derived units
What is the purpose of a unit in measurement?
To compare the physical quantity with a reference standard
What is the unit of the Planck constant?
J s
Which of the following systems of units was extensively used in the past?
All of the above
What is the term used to describe the process of expressing the units of physical quantities as combinations of base units?
Dimensional formulae
What is the term used to describe the set of base units and derived units?
System of units
What is the purpose of dimensional analysis?
To check the correctness of a physical equation
What is the term used to describe the minimum number of units required to express all physical quantities?
Base units
What is the relationship between the units of physical quantities?
They are related to each other through fundamental quantities
What is the base unit of length in the CGS system?
Centimetre
In which year was the SI system of units revised by the General Conference on Weights and Measures?
2018
What is the abbreviation for the International System of Units?
SI
What is the advantage of using SI units?
Conversions are quite simple and convenient
What is the base unit of mass in the FPS system?
Pound
How many base units are there in the SI system?
7
What is the name of the organization that developed the SI system?
Bureau International des Poids et measures
What is the base unit of time in the MKS system?
Second
Study Notes
Units and Measurement
- Two supplementary units are defined for plane angle dθ and solid angle dΩ.
- Plane angle dθ is the ratio of the length of arc ds to the radius r, and its unit is radian (symbol: rad).
- Solid angle dΩ is the ratio of the intercepted area dA of the spherical surface to the square of its radius r, and its unit is steradian (symbol: sr).
- Both radian and steradian are dimensionless quantities.
SI Base Quantities and Units
- There are seven base quantities in the International System of Units (SI).
- The base quantities and their corresponding units are:
- Length: metre (m)
- Mass: kilogram (kg)
- Time: second (s)
Introduction to Units and Measurement
- Measurement of a physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit.
- The result of a measurement is expressed by a number accompanied by a unit.
- Although there are many physical quantities, a limited number of units are needed to express them, since they are inter-related.
- Fundamental or base units are the units for the fundamental or base quantities.
- Derived units are the units of all other physical quantities, which can be expressed as combinations of the base units.
The International System of Units
- The International System of Units (SI) is the system of units currently internationally accepted for measurement.
- SI was developed by the Bureau International des Poids et Mesures (BIPM) in 1971 and revised in 2018.
- The SI system uses a decimal system, making conversions within the system simple and convenient.
- There are seven base units in the SI system, as listed in Table 1.1.
This quiz covers the units of measurement for plane angle and solid angle, including the definition of radian and its symbol.
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