Physics chapter 1 class11 notes
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Answer:
There are four fundamental forces which govern both macroscopic and microscopic
phenomena. There are
(i) Gravitational force
(ii) Nuclear force
(iii) Electromagnetic force
(iv) Weak force
The relative strengths of these forces are Fg
: Fw : Fe
: Fs = 1: : .
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
(c) 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 occurring on both sides
of the equation are the same.
If any equation is dimensionally correct it is not necessary that must be
mathematically correct too.
There are three main uses of the dimensional analysis-
(a) To convert a unit of given physical quantities from one system of units to another
system for which we use n2 = n1[M1/M2]a[L1/L2]b[T1/T2]c
(b) To check the correctness of a given physical relation.
(c) To derive a relationship between different physical quantities.
Significant figures: - The significant figures are normally those digits in a measured
quantity which are known reliably plus one additional digit that is uncertain.
For counting of the significant figure rule are as:
(i) All non- zero digits are significant figure.
(ii) All zero between two non-zero digits are significant figure.
(iii) All zeros to the right of a non-zero digit but to the left of an understood decimal point are
not significant. But such zeros are significant if they come from a measurement.
(iv) All zeros to the right of a non-zero digit but to the left of a decimal point are significant.
(v) All zeros to the right of a decimal point are significant.
(vi) All zeros to the right of a decimal point but to the left of a non-zero digit are not
significant. Single zero conventionally placed to the left of the decimal point is not
significant.
(vii) The number of significant figures does not depend on the system of units.
In addition or subtraction, the result should be reported to the same number of
decimal places as that of the number with minimum number of decimal places.
In multiplication or division, the result should be reported to the same number ofsignificant figures as that of the number with minimum of significant figures.
Accuracy refers to the closeness of a measurement to the true value of the physical
quantity and precision refers to the resolution or the limit to which the quantity is
measured.
Difference between measured value and true value of a quantity represents error of
measurement. It gives an indication of the limits within which the true value may lie.
Mean of n measurements
Absolute error Where = measured value it may be – positive,
negative or zero.
Mean absolute error
Relative error - it is the ratio of the mean absolute error to the true value.
SUMMARY
1. Physics deals with the study of the basic laws of nature and their manifestation indifferent
phenomena. The basic laws of physics are universal and apply in widely differentcontexts
and conditions.
2. The scope of physics is wide, covering a tremendous range of magnitude of
physicalquantities.
3. Physics and technology are related to each other. Sometimes technology gives rise tonew
physics; at other times physics generates new technology. Both have direct impact on society.There are four fundamental forces in nature that govern the diverse phenomena of
themacroscopic and the microscopic world. These are the ë gravitational force í, the ë
electromagnetic force í, the ë strong nuclear force í, and the ë weak nuclear force í .
Notification of different forces/domains in nature is a basic quest in physics.
5. The physical quantities that remain unchanged in a process are called
conservedquantities. Some of the general conservation laws in nature include the laws
ofconservation of mass, energy, linear momentum, angular momentum, charge, parity, etc.
Some conservation laws are true for one fundamental force but not for the other.
6. Conservation laws have a deep connection with symmetries of nature. Symmetries ofspace
and time, and other types of symmetries play a central role in modern theories of
fundamental forces in nature.