The angle between two directions (along which the planet is viewed) is measured. Let us assume that these positions are separated by distance AB = b. We observe the planet from two different positions A and B on the earth.
Let us assume that we need to measure the distance D of a far away planet S by parallax method.
Luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 × 10 12 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian. The amount of substance of a system, which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon – 12. The fraction 1/273.16 of the thermodynamic temperature of the triple point of water. The constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 m apart in vacuum would produce between these conductors a force equal to 10 × 10 -7 newton per meter of length. Kilogram is equal to the mass of the international prototype of the kilogram (a platinum-iridium alloy cylinder) kept at international Bureau of Weights and Measures, at Sevres, near Paris, France.ĭuration 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. Metre is the length of path travelled by light in vacuum during a time interval of 1/299,792,458 of a second. Physics Units Measurement Linear Motion Motion in Plane Law of Motion Work Energy Power Rotational Motion A complete set of these units is called the system of units. Such units for the derived quantities are called derived units.
Units of all other physical quantities can be expressed as combinations of the base units. The result of a measurement of a physical quantity is expressed by a number accompanied by a unit.įundamental Unit: The units for the fundamental or base quantities are called fundamental or base units. Measurement: Comparison of a physical quantity with certain basic, arbitrarily chosen internationally accepted reference standard (called unit) is called measurement.
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