ch 1 estimation and units

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Estimation and Units1. Estimation by orders of magnitude of size (length, area and volume), mass and time.

2. International System of Units and other commonly used metric units of the relevant

physical quantities.

A ConciseEstimation is a quick judgement about the magnitude of the

quantity.Physical Quantity : Any quantity that we study in Physics is known

as a Physical Quantity.Unit : The standard quantity is known as unit.Magnitude : The number of times, a standard quantity is present in

the physical quantity is known as the magnitude of Physical

Quantity.Physical quantity = (Magnitude) (Unit)

Fundamental Units : These are the units of the physical quantity

which are independent of any other units. The units of length, mass,time, temperature, luminous intensity and current are the

fundamental units.

Derived Units : These are the units of the physical quantity which

are dependent on the fundamental units. The units of area, volume,

force, pressure, momentum etc. are the derived units.Complementary Fundamental Units : Units of angle and solid angle

(Steradian).Methods of Obtaining Derived Units

Derived

Quantity Derivation Unit Symbol

(1) Area length length metre metre m2

(2) Speed

=distancetime

lengthtime

metresecond

m/s

or ms1

(3) Density

=MassVolume

mass

lengthlengthlength

kilogram

metremetremetre

kg/m3

or

kgm3


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(4) Velocity lengthtime

metresecond

m/s orms1

(5) Accelera

tion

velocitytime

metre

sec. sec.m/s2 orms2

(6) Momentum mass velocity kilogram metresecond

kg m/sor

kg ms1

(7) Force mass acceleration kilogram metre

sec. sec.

kg m/s2or

kg ms2

Magnitude of quantities, measured in physics, is generally

expressed in powers of ten.

100 = 1 101 =110 = 1

101 = 10 102 =1

10 10= 01

102 = 10 10 103 =1

10 10 10

103 = 10 10 10 and so on = 001 and so on.

There are certain prefixes used for very large and very small

measurements. These prefixes are very commonly used before gm (mass)

and m (length) :

(i) deca (da) = 101 (i) deci (d) = 101

(ii) hecto (h) = 102

(ii) centi (c) = 102

(iii) kilo (K) = 103 (iii) milli (m) = 103

(iv) Mega (M) = 106 (iv) micro () = 106

(v) Giga (G) = 109 (v) nano (n) = 109

(vi) Tera (T) = 1012 (vi) Pico (p) = 1012

(vii) Peta (P) = 1015 (vii) Femto (f) = 1015

(viii) Exa (E) = 1018 (viii) Atto (a) = 1018

Systems of Units(i) CGS : (Centimetre Gram Second)

(ii) MKS : (Metre Kilogram Second)(iii) SI : (Standard International)

SI System of Units

Quantity Unit Symbol

(i) Length Metre m

(ii) Mass Kilogramme kg

(iii) Time Second s

(iv) Temperature Kelvin K(v) Luminous Intensity Candela Cd


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(vi) Electric charge Coulomb C

(vii) Electric current Ampere A

(viii) Amount of Substance Mole mole

(ix) Angle Radian rd

(x) Solid angle Steradian st. rd

ch 1 estimation and units

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