Fundamental Physics Quick Revision 11th Standard 101-1b

101-1b

This part of the portion covers a summary of the fundamentals of units and measurements.

Units and measurements form the backbone of all things Physics as they provide both the qualitative and quantitative aspects of Physics meaning and understanding.

Facts considered, there are 7 fundamental quantities, i.e

Mass

Length

Time

Temperature

Current
Amount of substance

Luminous intensity 

Each of these have their own SI unit, namely

Mass - Kilogram (kg)

Length - Meter (m)

Time - Second (s)

Temperature - Degree Kelvin (K)

Current - Ampere (A)

Amount of substance - Avogadro Mole (mol)

Luminous intensity - Candela (c)

In this section, we discuss the fundamental quantities necessary for basic statics and kinematics, i.e

Length, Time and Mass.

Length 

The meter came to be defined as the distance between two fine lines engraved near the ends of a platinum – iridium bar, the standard meter bar, which was kept at the International Bureau of Weights and Measures near Paris. Accurate copies of the bar were sent to standardizing laboratories throughout the world. These secondary standards were used to produce other, still more accessible standards, so that ultimately every measuring device derived its authority from the standard meter bar through a complicated chain of comparisons. 
 
The meter was redefined as the distance traveled by light in a specified time interval.
In the words of the 17th General Conference on

Weights and Measures: 

This time interval was chosen so that the speed of light c is exactly c 299 792 458 m/s.
Measurements of the speed of light had become extremely precise, so it made sense to adopt the speed of light as a defined quantity and to use it to redefine the meter. Table 1-3 shows a wide range of lengths, from that of the universe (top line)

The meter is the length of the path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second. 

Time 

Time has two aspects. For civil and some scientific purposes, we want to know the time of day so that we can order events in sequence. In much scientific work, we want to know how long an event lasts. Thus, any time standard must be able to answer two questions: “When did it happen?” and “What is its duration?” 

To meet the need for a better time standard, atomic clocks have been developed.

The 13th General Conference on Weights and Measures in 1967 adopted a standard second based on the cesium clock:  

One second is the time taken by 9 192 631 770 oscillations of the light (of a specified wavelength) emitted by a cesium-133 atom.

Atomic clocks are so consistent that, in principle, two cesium clocks would have to run for 6000 years before their readings would differ by more than 1 s. Even such accuracy pales in comparison with that of clocks currently being developed; their precision may be 1part in 1018—that's, 1 in 1x1018 s(which is about 3x1010 y).

Mass

The SI standard of mass is a platinum–iridium cylinder (Fig. 1-3) kept at the International Bureau of Weights and Measures near Paris and assigned, by international agreement, a mass of 1 kilogram. Accurate copies have been sent to standardizing laboratories in other countries, and the masses of other bodies can be determined by balancing them against a copy. Table 1-5 shows some masses expressed in kilograms, ranging over about 83 orders of magnitude.