Fundamental Units - Units and Measurement, Class 11, Physics Video Lecture

fundamental units and definition in this
module we will discuss about definitions
of fundamental units in SI Mita M it is
a unit of length let us see the path of
light in a vacuum now we can define the
unit is the length of the path travelled
by light in vacuum during a time
interval of 1 by 299,792,458 or 4 second
second as it is a unit of time let us
see there is cesium 133 atom it is
defined as the duration of 9,192,631,770
periods of two radiations corresponding
to the transition between two hyperfine
levels of the cesium 133 atom kilogram
kg it is a unit of mass the kilogram is
equal to the mass of the International
prototype of the kilogram
platinum-iridium alloy cylinder kept at
International Bureau of weights and
measures
it serves near Paris of France ampere a
this is the unit of electric current the
ampere is that constant current which if
maintained in two straight 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 into 10 to the power minus 7
Newton per unit of length Kelvin this is
the unit of the thermodynamic
temperature the Kelvin is the fraction 1
by 273.16 of the thermodynamic
temperature of the triple point of
water mole this is the unit of quantity
of substance the mole is the amount of
substance of a system which contains as
many elementary entities as there are
atoms in 0.01 to kilograms of carbon 12
Candela
the Candela is the unit of luminous
intensity it is defined as in a given
direction of a source that emits
monochromatic radiation of frequency 540
into 10 to the power 12 Hertz and that
has a radiant intensity in that
direction of 1 by 683 wor thus the
radiant in that direction radiant
radiant rad this is the unit of plane
angle it is defined as the angle
subtended at the centre of a circle by
an arc whose length is equal to the
radius of the circle the Radian SR this
is the unit of solid angle stay Radian
is defined as a solid angle subtended at
the center of a sphere by its surface
whose area is equal to the square of the
radius of the sphere thank you