# FIRST LAW OF THERMODYNAMICS

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FIRST LAW OF THERMODYNAMICS

Introduction

This law was presented by Helm Holtz in 1847 in which he discussed the inter conversion of heat energy and l<.E of system w. r. t its total energy.

STATEMEMT

First law of thermodynamics is a form of law of conservation of energy According to which; “Energy can neither be created nor destroyed but can only converted from one form to another”.

It can be also stated as:

“It Heat Energy of a system is converted in to Mechanical Energy or Mechanical

Energy is converted into Heat Energy then the total energy of the system is remained same.”

EXPLANATION with MATHEMATICAL FORM

Consider a system consist of gas present in a container having moveable piston when “q” amount of heat energy is provided to the system. Its internal energy increases from “E, to EZ”, by using this energy gas expands so that piston covered a distance “∆h” so that “∆W” work is done by the piston and its volume increases from “v1” to

“V2” as shown in the figure.

Now according to 1st law of thermodynamics.

q = A E + ∆W

Here

q = heat absorb or release

E = internal energy of system

W = Work done

SIGN CONVENTION:

q —> absorb—> +ve

q —> release—> -ve

∆E —> increase—> +ve

∆E —> decrease —> -ve

∆W—> work done by system gas—> +ve

∆W —> work done on system —> -ve

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