## International System of Units – Class 11 | Chapter – 2 | Physics Short Notes Series PDF for NEET & JEE

* International System of Units*: The International System of Units (SI) is the modern form of the metric system and is the world’s most widely used system of measurement. It is a comprehensive system of measurement that is based on seven base units, which are used to derive all other units of measurement. The seven base units are the meter, kilogram, second, ampere, kelvin, mole, and candela.

*International System of Units*

**The 7 base units of the International System of Units (SI) are:**

- meter (m) for length
- kilogram (kg) for mass
- second (s) for time
- mole (mol) for amount of substance
- ampere (A) for electric current
- kelvin (K) for temperature
- candela (cd) for luminous intensity

The International System of Units (SI) is the modern form of the metric system and is the world’s most widely used system of measurement. It is based on seven base units, which are used to derive all other units of measurement:

the base unit of length, defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.**Meter (m):**the base unit of mass, defined as the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder kept at the International Bureau of Weights and Measures in France.**Kilogram (kg):**the base unit of time, defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.**Second (s):**the base unit of electric current, defined as the constant current that, if maintained in two parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 x 10**Ampere (A):**^{-7}newton per meter of length.the base unit of temperature, defined as 1/273.16 of the thermodynamic temperature of the triple point of water.**Kelvin (K):**the base unit of amount of substance, defined as the amount of substance that contains as many elementary entities (atoms, molecules, ions, etc.) as there are atoms in 0.012 kilograms of carbon-12.**Mole (mol):**the base unit of luminous intensity, defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 10**Candela (cd):**^{12}hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

*SI Derived Units*

The derived units are unlimited as they are formed by different operations on the base units. For derived units, the dimensions are expressed in terms of the dimensions of the base units. The derived units might also be expressed with the combination of base and derived units.

There are several derived units in physics. Some of the most widely used SI derived units in physics are given below.

Unit(s) Name |
SI Unit |
SI Unit Symbol |
Expressed in SI Base Unit |
Expressed in other SI units |
---|---|---|---|---|

Force, Weight | Newton | N | kg⋅m⋅s^{-2} |
– |

Frequency | Hertz | Hz | s^{-1} |
– |

Electric charge | Coulomb | C | s⋅A | – |

Electric potential (Voltage) | Volt | V | kg.m^{2}.s^{-3}.A^{-1} |
W/A |

Inductance | Henry | H | kg.m^{2}.s^{-2}.A^{-2} |
Wb/A |

Capacitance | Farad | F | kg^{−1}.m^{−2}.s^{4}.A^{2} |
C/V |

Resistance, Impedance, Reactance | Ohm | Ω | kg.m^{2}.s^{−3}.A^{−2} |
V/A |

Electrical conductance | Siemens | S | kg^{−1}.m^{−2}.s^{3}.A^{2} |
Ω−1 |

Magnetic flux | Weber | Wb | kg.m^{2}.s^{−2}.A^{−1} |
V⋅s |

Magnetic flux density | Tesla | T | kg.s^{−2}.A^{−1} |
Wb/m^{2} |

Energy, Work, Heat | Joule | J | kg.m^{2}.s^{−2} |
N⋅m = Pa⋅m^{3} |

Power, Radiant flux | Watt | W | kg.m^{2}.s^{−3} |
J/s |

Angle | Radian | rad | m.m^{−1} |
– |

Radioactivity | Becquerel | Bq | s^{-1} |
– |

Luminous flux | Lumen | lm | cd | cd⋅sr |

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