Chapter : Unit, Dimension & Error

Physical Quantities

The quantities by means of which we describe the laws of physics are called physical quantities. A physical quantity is completely specified if it has
(a) Magnitude only
Refractive index, dielectric constant
(b) Magnitude and unit
Mass, charge, current
(c) Magnitude, unit and direction
Displacement, torque.
Physical quantity = Magnitude × unit
1.1 Quantities : These are of two types –
(a) Fundamental quantities
(b) Derived quantities
(a) Fundamental quantities :
The quantities which do not depend upon other physical quantities are called fundamental quantities and all other quantities may be expressed in terms of the fundamental quantity.
There are of seven fundamental quantities in SI system-
(i) Mass
(ii) Length
(iii) Time
(iv) Temperature
(v) Electric current
(vi) Luminous intensity
(vii) Amount of substance
These quantities are also called base quantities.
(b) Derived quantities :
The quantities which are derived with the help of fundamental quantities is called derived quantities as Speed, i.e
Here we know that length and time are the fundamental quantities.

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