SSC CGL 2017 Exams Centers in Vijayawada, Physics Short Notes on PHYSICAL QUANTITIES (PART-1)

SSC CGL 2017 Exams Centers in Vijayawada, Physics Short Notes on PHYSICAL QUANTITIES (PART-1) 

PHYSICAL QUANTITIES 

           The quantities like length, mass, time, temperature, area, volume and density, etc. which can be measured, are known as physical quantities are speed and velocity, acceleration, pressure, energy, work power, electric current, luminous intensity, amount of substance, force, momentum, etc.
A physical quantity is represented by a number, followed by a unit. The ‘number plus unit’ is known as the ‘magnitude’ of the physical quantity.

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PHYSICAL QUANTITES ARE OF TWO TYPES:

    (I)   Basic physical quantities, and

    (ii)   Derived physical quantities,

BASIC PHYSICAL QUANTITIES

There are a total of 7 basic physical quantities. Length, mass, time, electric current, temperature, luminous intensity and amount of substance. All other quantities of physics can be expressed in terms of these physical quantities.

DERIVED PHYSICAL QUANTITIES

A physical quantity obtained by multiplying or dividing one basic physical quantity with another basic physical quantity, is known as a derived quantity.

The basic quantity are also known as base quantities. Basic quantities are fundamental quantities.

A unit is a quantity  of dimension used as a standard of measurement.

(i)          There should be a standard unit of measurement,

(ii)      A comparison should be made between the standard unit of measurement and the quantity to be measured.

INTERNATIONAL SYSTEM OF UNITS (SI UNITS)

The international system of units is called SI units in short. Actually, SI units is the short form of the French name  ‘Systeme International d’ ‘Units’ which means ‘International System of Units’ .

THE SEVEN BASE UNITS OF THE INTERNATIONAL SYSTEM OF MEASUREMENT:

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METRE

        Metre is the SI unit of length. A metre is the length of path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.

    

1 kilometre = 1000 metres

1 centimetre = 1/100 metre

1 millimetre = 1/1000 metre

KILOGRAM

Kilogram is the SI unit of mass.

1 quintal    =    100 kg

1 tonne      =    1000 kg

1 gram       =     1/1000 kg 

1 milligram  =  1/1000 gram

Kilogram is denoted by the symbol kg, gram by g and milligram by mg.

SECOND

Second is the SI unit of time.

60 seconds        =     1 minute

60 minutes        =     1 hour

24 hours             =    1 day

 AMIPERE

Ampere is the SI unit of electric current. The ampere is the constant current which, if maintained in two straight parallel conductors of infinite length and of negligible circular cross-section placed 1 metre apart in vacuum, would produce between them a force of 2 x 10-7 newtons per metre of length.

KELVIN

Kelvin is the SI unit of temperature. The triple point of water is temperature at which all the three phases of water (ice, liquid and water vapour) co-exist in dynamic equilibrium. The triple point of water has been assigned a temperature of 273.16 kelvin. The Kelvin is s1/273.16 of the thermodynamic temperature of the triple point of water.

MOLE

Mole is the SI unit of the amount of substance. A mole is the amount of substance which contains as many elementary particles (atoms, molecules or ions) as there are in 12 grams of carbon-12.

CANDELA

Candela is the unit of luminous intensity (luminous intensiy means brightness of light).

PREFIXES FOR USE WITH SI UNITS:

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