Contents
Advanced Physics Topics like quantum mechanics and relativity have revolutionized our understanding of the universe.
What are the Three States of Matter?
Technology is known to be the bridge between the concepts of science and their application for human needs. The rattling of the lid of a kettle containing boiling water led to the concept of the power of steam. Consequently, steam engines were constructed by technologists to utilise steam power directly for human needs. There are many similar examples.
The theory of the action of magnets on currents led to electric fans and motors, electromagnetic induction has been utilised to construct electricity producing dynamos in large power plants, the study of radioactivity produced nuclear bombs and nuclear power plants, and so on. In the modern applications of electronics, telecommunications, computers and internet, physics and technology march almost simultaneously. In these fields, there are almost no partition lines—physicists and technologists almost always complement each other.
Physics And Society
Physics has always provided very valuable contributions towards the necessities, amenities and luxury of our society. Man in this present society would not certainly have been able to live without the outcomes of physics like electricity, telecommunication, computers and internet. On the other hand, it must be noted that physics and its practices are nothing but parts of our society. As such, it enjoys the social virtues, and at this same time, cannot escape the social evils.
It is benefitted by the inherent human nature of pursuing knowledge, of the quest for novel developments. On the other hand, it had to be instrumental in the production of nuclear bombs. Proper funding, skilled human resource and other facilities towards physics are often minimal in some countries. It is obvious that the development of physics has always been and will always be closely interlinked with the development of our society as a whole.
Matter And Energy
Air, water, clay, sand and all such natural substances are made of matter. There are three types of matter-
- element,
- compound and
- mixture. Hydrogen, oxygen, etc. are examples of elements. Whereas water, common salt, etc. are compounds and air, milk, etc. are mixtures.
Matter manifests itself in the form of material bodies. A mate-rial body, simply called a body, has mass and occupies space.
In nature, every material body is observed to change its state frequently in some form or other. For example, a stone kept under direct sunlight becomes hot, napthalene balls decrease in size with time, water level in a beaker too decreases with time. During all such changes matter exchanges energy with its surroundings. Energy is generally described as the ability to do work. Energy manifests itself in nature in one of the following forms:
- mechanical energy,
- heat energy,
- light energy,
- sound energy,
- magnetic energy,
- electrical energy,
- chemical energy and
- nuclear energy.
In classical physics, nature has two entities—matter and energy. Both are indestructible. Matter can neither be created nor destroyed, it can only change from one form to another. Similar is the case with energy. These properties led to the formulation of
1. the law of conservation of mass and
2. the law of conservation of energy. Later, following Einstein’s theory of relativity, it was discovered that mass could be converted into energy (nuclear fission process) or energy into mass (production of electron-positron pair from a moving photon). This led to a single conservation law—the law of conservation of mass-energy.
Measurement of Physical Quantity
Some characteristics like smell, taste, colour, etc. of matter are subject to qualitative observations only. We use our sense organs to perceive these. On the other hand, some properties like mass or volume of a body, density of a matter, change in energy, etc. are subject to qualitative as well as quantitative observations. Measurement is an integral part of quantitative observation.
Characteristics of matter or energy that can be expressed as measurable quantities, are called physical quantities. Hence, the mass of a body is a physical quantity while its smell is not. Generally, the colour of a body is not a physical quantity but when the colour of light is represented by wavelength, then it is a physical quantity.
Measurements of many physical quantities involve a mea-surement of time also. Thus, time is also treated as a physical quantity, though time is not a direct characteristic of matter or energy.
One of the most important targets of physics is to measure physical quantities with accuracy. Observation of a physical quantity is meaningful only when it is measured and is expressed as a numerical value with a proper unit.
Units of Measurement
The result of measurement of any physical quantity is expressed in terms of its unit which is unique to that physical quantity and sets a standard for its measurement. Any measurement is therefore written as a number of times this standard value. The standard of measurement of any physical quantity is represented by 1 and the name of the unit is written beside 1. Therefore, the value of a physical quantity = ‘number’ ‘unit’.
Example: Suppose the length of a rod is 3 metre or 3 × 1 m. Here length is the physical quantity, metre (m) is the unit of length and the digit 3 implies that the length is 3 times the value of 1 metre (which is the standard of measurement of length).
To measure a physical quantity, the unit chosen should be
- of convenient size,
- unambiguous,
- reproducible,
- invariant under change of space and time and
- acceptable to all.
Base or fundamental units and derived units: There are hundreds of physical quantities in nature. Accordingly, their measurements demand hundreds of different units. If we start to assign one different unit to each of them, the entire measurement procedure would soon go beyond our control. Fortunately, this is not actually necessary. It is observed that different physical quantities have very familiar relationships among them. As such, these units also have definite relations among them. So it is possible to
- mark a few physical quantities that are independent of one another,
- assign a convenient initial unit for each of them, and then
- prepare appropriate units for all other physical quantities in terms of those initial units, using the well-known relationships among different quantities.
The initial independent units are called the base units or fundamental units and all other units structured from them are called the derived units.
Length, mass and time—these are three quantities entirely independent of one another. So long as our study is concen-trated to mechanics, these three fundamental units of length, mass and time can serve our purpose of measurement. But these units are not sufficient for the study of whole of physics.
So it was decided to widen the scope of measurement by introducing some more fundamental quantities thereby increasing their number from three to seven. It is observed that all other physical quantities are somehow related to or can be structured from the seven base units. They are the derived units. This simplifies the measurement procedure since it is no more necessary to create a new unit for every measurable quantity.
Example: From the units of the three fundamental quantities
- metre (m) for length,
- kilogram (kg) for mass and
- second (s) for time, we can structure the units of other quantities. A few examples are given here :
i) Volume (V): For a rectangular parallelepiped, volume = length × breadth × height. Actually, length, breadth and height belong to the same physical quantity—the unit of each of them is metre.
So, the unit of volume = m × m × m – m3.
ii) Density (ρ): By definition, ρ =
So, the unit of density = \(\frac{\mathrm{kg}}{\mathrm{m}^3}\) = kg/m3 = kg ᐧ m-3.
iii) Velocity (v): By definition, v \(=\frac{\text { displacement }}{\text { time }}\)
Displacement is measured in units of length, i.e., metre.
So, the unit of velocity = \(\frac{\mathrm{m}}{\mathrm{s}}\) = m/s = m ᐧ s-1.