Unit and Dimensions Class 11

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Physics and Measurement


Physics, Technology and Society, S.I. Units, Fundamentals and Derived Units. Least count, accuracy and precision of measuring instruments, Errors in measurement, Dimensions of Physical quantities, dimensional analysis and its applications.

Physics in Relation to Society
The future of society is intimately related to physics. Since, whatever is thought or discovered in physics, it immediately affects society. The advancements in the field of communication, such as Mobile Phone, Fax, teleprinter and telex etc enable us to quickly exchange messages between far off places. The Radio and Television have made it possible to have instant communication with the other parts of the world. The launching of satellites into space has totally revolutionised the concept of communication. One can instantly see anything happening in any part of the world. Microelectronics, lasers, computers, superconductivity and nuclear energy have brought about a profound change in the thinking and living style of human beings.
The degree of impact of Science and Technology on society can easily be gauged from the following words reported to have been said by the great scientist and philosophers
“Science is a method for describing, creating and understanding human experience.”
—R. Bruce Lindsay,
It will be no exaggeration if we say that science in general and physics, in particular, has the potential to eradicate poverty and hunger completely from the surface of the earth and to use it in an age of prosperity.
 Physics in relation to science: Physics is the most basic of all the sciences and it has played a very important role in the development of other sciences.
 Physics in relation to mathematics: Physics is a quantitative science. The theories in physics make use of various mathematical concepts and it has proved to be the most powerful tool in the development of theoretical physics
 Physics in relation to chemistry: The study of the structure of the atom, radioactivity X-ray diffraction etc. has brought about a revolution in the present day chemistry. These studies helped to rearrange elements in the periodic table, to detect even bonding, to understand complex chemical structures etc.
Physics in relation to technology: Technology is the application of science in general and physics in particular for practical purposes. A few advancements have been made in technology on the basis of physics.
The study of lever systems has helped to design a large number of very useful machines.  The study of satellites has made it possible to forecast weather very accurately.  The discovery of nuclear fission has proved to be a tremendous source of energy. In nuclear power stations and nuclear bonds, a large amount of energy becomes valuable due to the conversion of mass into energy.
However, if the laws and discoveries of physics are not used in a responsible way, it may prove a curse for society. Nuclear weapons can destroy all of humanity in no time.
Forces in nature: There are four types of fundamental forces operative in nature,
(i) Gravitational force
(ii) Electromagnetic force
(iii) Strong nuclear force
(iv) Weak nuclear force
Gravitational force: According to Newton’s law of gravitation, the force of attraction (F), between two objects (of masses M1 and M2) held at a distance (r) apart is given as 29

where G = Gravitational constant = 6.66 × 10–11 N-m2 Kg–2. Gravitational force obeys the inverse square law. It is a long range force (extending up to infinity), always attractive but the weakest force in nature. It is a conservative force.
Examples of gravitational force in daily life:
(a) The gravitational force of earth keeps the satellite revolving around it.
(b) Due to the gravitational force of earth all objects near its surface fall towards its centre.
(c) The gravitational force of moon causes tides in the seas.
(d) The gravitational force of the sun accounts for the motion of planets around it.

Electromagnetic forces: These include electric and magnetic forces. The electrostatic force (F) between two charges (q1 and q2) held at a distance or apart, governed by the Coulomb’s law, is given as


where k = a constant = 9 × 109 Nm2 C–2 (in space)
A moving charge produces a magnetic field around it. When the two charges are in motion, both produce a magnetic field around themselves. Then, the charge (q) moving with velocity (v), inside the magnetic field (B) produced by the other charge, experiences electromagnetic force (F) gives as

Electromagnetic force obeys the inverse square law. It is also a long range force which may be attractive or repulsive. It is 1036 times stronger than gravitational force between two protons. It is a conservative force.
Examples of electromagnetic force in daily life :
(a) In a substance, electrons revolve around the nucleus of each of its atoms. The revolving electrons of one atom interact with those of another atom. The electromagnetic force between them holds them together to form a molecule.
(b) Two parallel conductors carrying currents in the same direction attract each other due to the electromagnetic force.
(c) In a cyclotron, alpha-particles are placed in the magnetic field. It experiences an electromagnetic force due to which it is accelerated.
Strong Nuclear Force: The forces operating inside the nucleus of an atom between the nucleus are called nuclear forces. It is a short range attractive force. It varies inversely with some higher power of distance. The relative strength of various forces is (between two protons),


Examples of nuclear force in daily life:

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