What are the 7 basic SI units?
2 Answers
The International System of Units (SI) is a globally accepted system for measuring various physical quantities. It is based on seven fundamental units, each representing a different dimension of measurement. These seven basic SI units are:
1. **Meter (m)** - This is the unit of length. It is defined as the distance traveled by light in a vacuum in \( \frac{1}{299,792,458} \) seconds. The meter provides a standard way to measure distance or length.
2. **Kilogram (kg)** - This is the unit of mass. It is defined as the mass of the international prototype of the kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM). The kilogram is used to measure the amount of matter in an object.
3. **Second (s)** - This is the unit of time. It is 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 cesium-133 atom. The second is the standard unit for measuring time.
4. **Ampere (A)** - This is the unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to \( 2 \times 10^{-7} \) newtons per meter of length. The ampere measures the flow of electric charge.
5. **Kelvin (K)** - This is the unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water. The Kelvin scale starts from absolute zero, the point at which all molecular motion ceases.
6. **Mole (mol)** - This is the unit of amount of substance. It is defined as the amount of substance that contains exactly \( 6.02214076 \times 10^{23} \) elementary entities (e.g., atoms, molecules). This number is known as Avogadro's number. The mole is used to measure quantities of chemical substances.
7. **Candela (cd)** - This is the unit of luminous intensity. It is defined as the luminous intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) Hz and has a radiant intensity in that direction of \( \frac{1}{683} \) watt per steradian. The candela measures the perceived power of light.
These units form the foundation of the SI system and are used to express measurements in science, engineering, and everyday life. Each unit is defined with precision to ensure consistency and accuracy in measurements globally.
1. **Meter (m)** - This is the unit of length. It is defined as the distance traveled by light in a vacuum in \( \frac{1}{299,792,458} \) seconds. The meter provides a standard way to measure distance or length.
2. **Kilogram (kg)** - This is the unit of mass. It is defined as the mass of the international prototype of the kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM). The kilogram is used to measure the amount of matter in an object.
3. **Second (s)** - This is the unit of time. It is 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 cesium-133 atom. The second is the standard unit for measuring time.
4. **Ampere (A)** - This is the unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to \( 2 \times 10^{-7} \) newtons per meter of length. The ampere measures the flow of electric charge.
5. **Kelvin (K)** - This is the unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water. The Kelvin scale starts from absolute zero, the point at which all molecular motion ceases.
6. **Mole (mol)** - This is the unit of amount of substance. It is defined as the amount of substance that contains exactly \( 6.02214076 \times 10^{23} \) elementary entities (e.g., atoms, molecules). This number is known as Avogadro's number. The mole is used to measure quantities of chemical substances.
7. **Candela (cd)** - This is the unit of luminous intensity. It is defined as the luminous intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) Hz and has a radiant intensity in that direction of \( \frac{1}{683} \) watt per steradian. The candela measures the perceived power of light.
These units form the foundation of the SI system and are used to express measurements in science, engineering, and everyday life. Each unit is defined with precision to ensure consistency and accuracy in measurements globally.
The International System of Units (SI) is a standardized system of measurement used worldwide in science, industry, and everyday life. It consists of seven basic units, each representing a fundamental physical quantity. These units are:
1. **Meter (m)** - This is the unit of length. It is defined as the distance that light travels in a vacuum in \( \frac{1}{299,792,458} \) seconds. The meter provides a measure of distance or spatial extent.
2. **Kilogram (kg)** - This is the unit of mass. It is defined by taking the fixed numerical value of the Planck constant \( h \) to be \( 6.62607015 \times 10^{-34} \) when expressed in the unit \( \text{kg} \cdot \text{m}^2 \cdot \text{s}^{-1} \). The kilogram measures the amount of matter in an object.
3. **Second (s)** - This is the unit of time. It is 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 cesium-133 atom. The second measures the progression of time.
4. **Ampere (A)** - This is the unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in a vacuum, would produce between these conductors a force equal to \( 2 \times 10^{-7} \) newton per meter of length. The ampere measures the flow of electric charge.
5. **Kelvin (K)** - This is the unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water. The Kelvin scale starts from absolute zero, where all molecular motion ceases.
6. **Mole (mol)** - This is the unit of the amount of substance. It is defined as the amount of substance that contains as many elementary entities (such as atoms, molecules, ions) as there are atoms in \( 0.012 \) kilograms of carbon-12. The mole measures the quantity of particles in a sample.
7. **Candela (cd)** - This is the unit of luminous intensity. It is defined as the intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) Hz and has a radiant intensity of \( \frac{1}{683} \) watt per steradian. The candela measures the amount of light emitted by a source.
Each of these units serves as the foundation for other derived units and provides a consistent framework for scientific measurement and communication globally.
1. **Meter (m)** - This is the unit of length. It is defined as the distance that light travels in a vacuum in \( \frac{1}{299,792,458} \) seconds. The meter provides a measure of distance or spatial extent.
2. **Kilogram (kg)** - This is the unit of mass. It is defined by taking the fixed numerical value of the Planck constant \( h \) to be \( 6.62607015 \times 10^{-34} \) when expressed in the unit \( \text{kg} \cdot \text{m}^2 \cdot \text{s}^{-1} \). The kilogram measures the amount of matter in an object.
3. **Second (s)** - This is the unit of time. It is 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 cesium-133 atom. The second measures the progression of time.
4. **Ampere (A)** - This is the unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one meter apart in a vacuum, would produce between these conductors a force equal to \( 2 \times 10^{-7} \) newton per meter of length. The ampere measures the flow of electric charge.
5. **Kelvin (K)** - This is the unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water. The Kelvin scale starts from absolute zero, where all molecular motion ceases.
6. **Mole (mol)** - This is the unit of the amount of substance. It is defined as the amount of substance that contains as many elementary entities (such as atoms, molecules, ions) as there are atoms in \( 0.012 \) kilograms of carbon-12. The mole measures the quantity of particles in a sample.
7. **Candela (cd)** - This is the unit of luminous intensity. It is defined as the intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) Hz and has a radiant intensity of \( \frac{1}{683} \) watt per steradian. The candela measures the amount of light emitted by a source.
Each of these units serves as the foundation for other derived units and provides a consistent framework for scientific measurement and communication globally.