1377953416-PHYSICSNOTES.docx (Size: 109.75 KB / Downloads: 9) Physical World And Measurement
Physical World And Measurement
There are four fundamental forces which govern both macroscopic and
microscopic phenomena. There are
(i) Gravitational force (iii) Electromagnetic force
(ii) Nuclear force (iv) Weak force
The relative strengths of these forces are
All those quantities which can be measured directly or indirectly and in terms of
which the laws of physics can be expressed are called physical quantities.
(a) Fundamental quantities (b) Derived quantities.
The units of the fundamental quantities called fundamental units , and the units of
derived quantities called derived units.
System of units:-
(a) MKS (b) CGS © FPS (d) SI
• The dimensions of a physical quantity are the powers to which the
fundamental quantities are raised to represent that physical quantity.
• The equation which expresses a physical quantity in terms of the fundamental
units of mass, length and time, is called dimensional equation.
• According to this principle of homogeneity a physical equation will be
dimensionally correct if the dimensions of all the terms in the all the terms
Absolute error ( Δa ) = amean - ai Where ai = measured value
It may be - positive, negative or zero.
(i) Mean absolute error
(ii) Relative error - it is the ratio of the mean absolute error to the true
δa = I Δa I/ amean
(iii) The relative error expressed in percent is called percentage error.
The error is communicated in different mathematical operations as detailed below:
(i) For x = (a ± b), Δx = ± ( Δa + Δb)
(ii) For x = a x b , Δx/x = ± ( Δa/a + Δb/b)
(iii) For x = a/b , Δx/x = ± ( Δa/a + Δb/b)
(iv) For x= an