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In a private school a physics teacher was asked by her student how to understand first law of thermodynamics in an easier way by using hints or any examples. The teacher was also thinking for a long time and when she was taking classes for 12^(th) standard students about Einstein's photoelectric equation, she was striked with an idea for clearing doubt of her 11^(th) std students. Can you guess her idea? (i) Define degrees of freedom? |
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Answer» Solution :The lady teacher explained first law of thermodynamics comparing Einstein's photo electric EQUATION. When an photo of energy (of some joule) INCIDENT on a metal surface, a part of the energy of the photon will be used to eject electrons from each atm in the metal surface (i.e. system) and remaining part of energy of the photon will be used to IMPART kinetic energy to the ejected electrons. Here the energy of photon is compared with heat energy `(DeltaQ)`. supplied to the gas (system). A part of the energy of `DeltaQ` will be used in increasing the internal energy of the gas by increasing its temperature. This is compared with the kinetic energy in the case of photoelectric equation and after gaining temperature. The molecules that are excited expands and does some work on the system. This is compared with the work function in photoelectric equation i.e. `DeltaQ=DeltaU+DeltaW` (i) Degrees of freedom : The minimum number of independent coordinates needed to specify the POSITION and CONFIGURATION of a thermodynamical system in space is called degrees of freedom of the system. Ex : A particle moving in space has 3 degrees of freedom. |
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