What are the 7 SI units?
2 Answers
The International System of Units (SI) is a standardized system of measurement used worldwide. It is based on seven base units, which are defined by fundamental physical constants and phenomena. Each base unit corresponds to a different type of physical quantity. Here are the seven SI base units:
1. **Meter (m)** - The SI unit of length. It is defined as the distance that light travels in a vacuum in \( \frac{1}{299,792,458} \) seconds.
2. **Kilogram (kg)** - The SI unit of mass. It is defined by the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
3. **Second (s)** - The SI unit of time. It is defined based on the vibrations of cesium atoms, specifically 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.
4. **Ampere (A)** - The SI unit of electric current. It is defined by the flow of electric charge through a conductor; specifically, one ampere is the current that, when flowing through two parallel conductors one meter apart in a vacuum, produces a force of \( 2 \times 10^{-7} \) newtons per meter of length between them.
5. **Kelvin (K)** - The SI unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water, which is the point where water coexists in three phases (solid, liquid, and gas) in equilibrium.
6. **Mole (mol)** - The SI unit of amount of substance. It is defined as the amount of substance that contains as many entities (such as atoms, molecules, or ions) as there are in 12 grams of carbon-12. This number is approximately \( 6.022 \times 10^{23} \), known as Avogadro's number.
7. **Candela (cd)** - The SI unit of luminous intensity. It is defined as the intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) hertz and that has a radiant intensity of \( \frac{1}{683} \) watt per steradian in that direction.
These base units are the foundation of the SI system and can be combined to form derived units for more complex measurements.
1. **Meter (m)** - The SI unit of length. It is defined as the distance that light travels in a vacuum in \( \frac{1}{299,792,458} \) seconds.
2. **Kilogram (kg)** - The SI unit of mass. It is defined by the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
3. **Second (s)** - The SI unit of time. It is defined based on the vibrations of cesium atoms, specifically 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.
4. **Ampere (A)** - The SI unit of electric current. It is defined by the flow of electric charge through a conductor; specifically, one ampere is the current that, when flowing through two parallel conductors one meter apart in a vacuum, produces a force of \( 2 \times 10^{-7} \) newtons per meter of length between them.
5. **Kelvin (K)** - The SI unit of thermodynamic temperature. It is defined as the fraction \( \frac{1}{273.16} \) of the thermodynamic temperature of the triple point of water, which is the point where water coexists in three phases (solid, liquid, and gas) in equilibrium.
6. **Mole (mol)** - The SI unit of amount of substance. It is defined as the amount of substance that contains as many entities (such as atoms, molecules, or ions) as there are in 12 grams of carbon-12. This number is approximately \( 6.022 \times 10^{23} \), known as Avogadro's number.
7. **Candela (cd)** - The SI unit of luminous intensity. It is defined as the intensity of a source that emits monochromatic radiation of frequency \( 540 \times 10^{12} \) hertz and that has a radiant intensity of \( \frac{1}{683} \) watt per steradian in that direction.
These base units are the foundation of the SI system and can be combined to form derived units for more complex measurements.
The International System of Units (SI) is based on seven fundamental units, each of which represents a specific physical quantity. These units are the building blocks for all other measurements in the SI system. Here are the seven SI base units:
1. **Meter (m)** - The unit of length. It is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
2. **Kilogram (kg)** - The unit of mass. It is defined as the mass of the international prototype of the kilogram, which is a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
3. **Second (s)** - 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.
4. **Ampere (A)** - The unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length and negligible cross-section, and placed 1 meter apart in a vacuum, would produce a force between these conductors equal to 2 × 10⁻⁷ newtons per meter of length.
5. **Kelvin (K)** - The unit of thermodynamic temperature. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
6. **Mole (mol)** - The unit of amount of substance. It is defined as the amount of substance that contains exactly 6.02214076 × 10²³ elementary entities (such as atoms, molecules, ions, etc.), which is Avogadro's number.
7. **Candela (cd)** - The unit of luminous intensity. It is 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.
These units provide a standardized way to measure physical quantities, making scientific communication and calculations more consistent and accurate worldwide.
1. **Meter (m)** - The unit of length. It is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
2. **Kilogram (kg)** - The unit of mass. It is defined as the mass of the international prototype of the kilogram, which is a platinum-iridium cylinder kept at the International Bureau of Weights and Measures (BIPM) in France.
3. **Second (s)** - 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.
4. **Ampere (A)** - The unit of electric current. It is defined as the constant current which, if maintained in two straight parallel conductors of infinite length and negligible cross-section, and placed 1 meter apart in a vacuum, would produce a force between these conductors equal to 2 × 10⁻⁷ newtons per meter of length.
5. **Kelvin (K)** - The unit of thermodynamic temperature. It is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.
6. **Mole (mol)** - The unit of amount of substance. It is defined as the amount of substance that contains exactly 6.02214076 × 10²³ elementary entities (such as atoms, molecules, ions, etc.), which is Avogadro's number.
7. **Candela (cd)** - The unit of luminous intensity. It is 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.
These units provide a standardized way to measure physical quantities, making scientific communication and calculations more consistent and accurate worldwide.