Symmetry

Symmetry in Physical Laws

'Symmetry' has a special meaning in physics. A picture is said to be symmetrical if one side is somehow the same as the other side. Precisely, a thing is symmetrical if one can subject it to a certain operation and it appears exactly the same after the operation. For example, if we look at a base that is left and right symmetrical, then turn it 180° around the vertical axis it looks the same. Newton's laws of motion do not…

Statistical Physics: Macrostates and Microstates

Consider some (4, say) distinguishable particles. If we wish to distribute them into two exactly similar compartments in an open box, then the priori probability for a particle of going into any one of the compartments will exactly 1/2 as both compartments are identical. If the four particles are named as a , b, c and d and the compartments as compartment 1 and compartment (2), then following table can be made listing all the possible arrangements. $ Compartment (1)…

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Statistical Physics: Ensembles

Ensembles: As a system is defined by the collection of a large number of particles, so the "ensembles" can be defined as collection of a number macroscopically identical but essentially independent systems. Here the term macroscopically independent means, as, each of the system constituting an ensemble satisfies the same macroscopic conditions, like Volume, Energy, Pressure, Temperature and Total number of particles etc. Here again, the term essentially independent means the system (in the ensemble) being mutually non-interacting to others, i.e.,…

Rayleigh- Jean’s Law

Lord Rayleigh on classical limes made an attempt to explain the energy distribution in black body radiation, which was completed by Jeans in 1900. The result obtained by then is known as Rayleigh - Jean's Law. Black body emits radiation of continuously variable wavelength right from zero to infinity. This radiation can be imagined as broken up into monochromatic waves. These monochromatic waves originate as a result of a different modes of vibration of the medium, which at that time…

Wein’s Laws

Various workers tried to explain the problem of energy distribution in black body radiation and finally the problem was successfully solved by German Physicist Max Planck. Before him, German Physicist Wilhelm Wein and British Physicist Lord Rayleigh & James Jean have tackled this problem and have given important laws. In fact, the work of their scientists paved the way for Planck to give his famous theory of radiation. In this series of articles, I shall be discussing the various laws,…

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Entropy and Disorder

In science, we look for patterns to discover nature's laws. What is the pattern common to all spontaneous changes? To find a pattern, it is often best to start with very simple examples, because then the pattern is likely to be more obvious. So let's think about two simple spontaneous changes -- the cooling of a hot metal and the expansion of a gas -- at a molecular level and search for their common feature. https://www.youtube.com/watch?v=ZsY4WcQOrfk A hot block of…