# I learned it today – understanding length in metres

Speed of light =299792458m/s 0r approx 300000km/sec

Second= 9192631770 cycles of the standard caesium 133 atom(55) transition (electron vibration pulse)- in future optical clocks because of less uncertainty

Metre= the length of the path travelled by light in a vacuum during a time interval of 1/299792458 of a second

Pm=Picometer unit of length equivalent to one trillionth of a meter.

NM=nanometre unit of length equal to one billionth of a meter.

Micrometer unit of length equals one millionth of a metre.

Millimetre unit of length equals to 1000th of a metre

Centimetre unit of length is equals to 100th of a metre

Metric prefixes

Zetta meter 10^21m

Tera     10^12

Giga     10^9

Mega    10^6

Kilo       10^3

Hecto    10^2

Deca     10^1

None     10^0

Deci      10^-1

Centi     10^-2

Milli       10^-3

Micro     10^-6 – chromosome level

Nano     10^-9 – polymer of DNA level

Pico      10^-12- gamma ray wavelength level

Femtometre 10^-15-quarks

Yoctometer   10^-30

Smallest length theorised= PLANCK LENGTH = 1.6×10^-35 metres

If atom is size of earth than an proton of object in that earth would be a planck length

Last size where gravity would have an effect -size of string in string theory

Space time fabric =9.5 x 10^-36

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