Physics And Measurement

Physics And Measurement

Physics:

 It is the study of the properties of matter, energy and there mutual relationship..........more Details.

Measurement: 

Measurement of any thing means comparing it with some standards to see how many times as big it is. The standard with which things are compared is called unit. Magnitude of a physical quantity means a number and a proper unit.

Physical Quantities:

All measurable quantities are physical quantities. e,g volume, speed, fore, time, density, temperature and electric current etc. Physical quantities are classified into two categories.

1. Base Quantities: The minimum number of these physical quantities in terms of which other physical quantities can be defined.
2. Derived Quantities: Those quantities whose definitions are based on other physical quantities( which are base quantities). 

System Of Units:

A complete set units, both base and derived, for all kinds of physical quantities is called a system of unites. A few system of units used in all over the world are... 

Meter, Kilometer, Second = M.K.S

Foot, Pound, Second = F.P.S

Centimeter, Gram, Second= C.G.S

System International= SI

• Base Units:

Standard Units Of Length:

• Definition 1: The standard unit of length is mete. One meter is the distance between two finely drawn  lines on Platinum - Iridium metal bar placed in the International Bureau of weight measures at serves France.
• Definition 2: One meter is the distance traveled by weight in vacuum during a time of 1/299792458 seconds.

Unit Of Mass: 

The SI unit of mass is Kilogram, which is the mass of a Platinum- Iridium cylinder kept at international Bureau of weight and measures at severs, France.

Unite Of Time:  

• Definition 1: Second is the basic unit of time. One second is one mean solar second.                                       1 second  = 1/60 x 1/60 x 1/60 Mean solar days.
• Definition 2: Characteristic frequency of Cesium- 133(Cs-133) atom.                                                                                  1 second = Duration of 9,192,631,770 Vibrations of Cs- 133.

Unit of Temperature:

The standard unit of temperature is Kelvin. It is fraction 1/273.16 of the temperature of triple point of water. the triple point of water means the temperature at which solid ice, liquid water and vapors of water co-exist in equilibrium in three phases.  

Standard Unit of Current:

The Unit of current is ampere. One ampere is defined as the constant current that, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section and placed one meter apart in a vacuum would produce between these conductor a force equal to 2x10^-7 newton per meter of length.

Unit of Luminous Intensity: The Unit of Luminous intensity is Candela. The Luminous intensity in the perpendicular direction of a surface of 1/600,000 m² of  a block body at the temperature of freezing platinum at standard atmospheric pressure.

Unit of Amount of Substance: The SI unit of a substance is one mole. One mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.12 kilograms of Carbon-12.

                          The elementary entities must be specified and may be atoms , molecules, ions, electrons, other particles or specified group of particles.

• Derived Units:

    Any unit formed by Multiplying or dividing a base unit by another base unit is a derived unit. some of the derived units are given in the table

Physical Quantities

Units

Symbol

In term of Base Units

Force	Newton	N	Kgms¯²
Work	Joule	J	Nm = Kgm²s¯²
Power	Watt	W	Js¯¹  = Kg
Electric Charge	Coulomb	C	As
Potential Difference	Volt	V	JA¯¹ s¯¹
Pressure	Pascal	Pa	Nm¯²=Kgm¯¹s¯²

Supplementary Units: Those units which has not yet classified in either base units or derived units, those SI units are called supplementary Units, which are the Plain angle and solid angle.

Unit of Plane Angle (Radian): The unit of plane angle is radian. A radian is defined as the plane angle substended at the center of a circle by an arc of length equal to the radius. The angle ∠OA in the figure is one radian, since the arc length "AC" is equal to the radius "OA". If "θ" IS measured in radius then

                                              

                                                 θ=s⁄r ---------->  (1)

Where "r" is radius and "s" is the length of the arc. Since the length of circumference of circle is S=2πr. According to the above definition and equation (1) 

We get angle as 

                                      θ= 2πr/r  radian
                         θ= 2π      radian----------->(2)

But the total angle substended by a circle on the center of circle, if measured in degree is given as,
                                       θ= 360°------------>(3)
So comparing equation (2) and equation (3)
                                       θ=2π radian =  360°
                                      OR
                           1 radian=360°/2π
                           1 radian=57.32°

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