Special Length units
|
Unit name |
Unit Symbol |
Value in meters |
|
fermi |
f |
10-15 m |
|
angstrom |
Å |
10-10m |
|
astronomical unit(average distance of sun from earth) |
AU |
1.496 X 1011 m |
|
light year(distance travelled by light in 1 year with velocity 3 X 108 m/s) |
ly |
9.46 X 1011 m |
|
parsec(distance at which average radius of earth’s orbits subtends an angle of 1 arc second) |
pc |
3.08 x 1016 m |
Measurement of Mass
Mass is usually measured in terms of kg but for atoms and molecules, unified atomic mass unit (u) is used.
1 u = 1/12 of the mass of an atom of carbon-12 isotope including mass of electrons (1.66 x 10-27 kg)
Apart from using balances for normal weights, mass of planets is measured using gravitational methods and mass of atomic particles are measured using mass spectrograph (radius of trajectory is proportional to mass of charged particle moving in uniform electric and magnetic field).
Range of Mass
|
Object |
Mass (kg) |
|
Electron |
10-30 |
|
Proton |
10-27 |
|
Red Blood Cell |
10-13 |
|
Dust particle |
10-9 |
|
Rain drop |
10-6 |
|
Mosquito |
10-5 |
|
Grapes |
10-3 |
|
Human |
102 |
|
Automobile |
103 |
|
Boeing 747 aircraft |
108 |
|
Moon |
1023 |
|
Earth |
1025 |
|
Sun |
1030 |
|
Milky way Galaxy |
1041 |
|
Observable Universe |
1055 |
Measurement of Time
Time is measured using a clock. As a standard,atomic standard of time is now used, which is measured by Cesium or Atomic clock.
- In Cesium clock, a second is equal to 9,192,631,770 vibrations of radiation from the transition between two hyperfine levels of cesium-133 atom.
- Cesium clock works on the vibration of cesium atom which is similar to vibrations of balance wheel in a regular wristwatch and quartz crystal in a quartz wristwatch.
- National standard time and frequency is maintained by 4 atomic clocks. Indian standard time is maintained by a Cesium clock at National Physical Laboratory (NPL), New Delhi.
- Cesium clocks are very accurate and the uncertainty is very low 1 part in 1013 which means not more than 3 μs are lost or gained in a year.
Range of Time
|
Event |
Time Interval (s) |
|
Life span of most unstable particle |
10-24 |
|
Period of x-rays |
10-19 |
|
Period of light wave |
10-15 |
|
Period of radio wave |
10-6 |
|
Period of sound wave |
10-3 |
|
Wink on an eye |
10-1 |
|
Travel time of light from moon to earth |
100 |
|
Travel time of light from sun to earth |
102 |
|
Rotation period of the earth |
105 |
|
Revolution period of the earth |
107 |
|
Average human life span |
109 |
|
Age of Egyptian pyramids |
1011 |
|
Time since dinosaur extinction |
1015 |
|
Age of Universe |
1017 |