thermal_5_02_08_2011

# thermal_5_02_08_2011 - The First Law of Thermodynamics...

This preview shows pages 1–7. Sign up to view the full content.

The First Law of Thermodynamics Lecture 5

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
First Law of Thermodynamics Overlooks the fine microscopic details (which in many cases are irrelevant). Describes the conversion of one form of energy (heat) into other forms Important Consequences: Conservation of energy Allows estimates of maximum efficiency of energy conversion Completely General! (not just ideal gas) 1 st Law
The Effect of Heat “Distributed” Energy http://mw2.concord.org/public/part2/heat/page8.cml 1 click

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
E int E int = Q + W Statement of 1 st Law (1842) E int represents the distributed energy in a closed system. It can contain contributions from a variety of sources like thermal, chemical, etc. Sign conventionl
The “system” Universal Appeal! The “system” can be a collection of matter in any form, separated from its surroundings by real or imaginary boundaries. The system may be a biological cell, the contents of a test tube, the gas in a piston, a thin film, or a cup of coffee. How you define a “system” depends on the problem you want to solve.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
If work is done ON a system, it is assigned a positive sign If work is done BY a system (external work or work on the environment), it is assigned a negative sign Sign Conventions When using the 1 st Law, it’s important to determine the proper signs Note: This sign convention is consistent with definition in mechanics in hich work done on a system (eg lifting a box) increases the mechanical Heat (Q) also has a sign associated with it: If system GAINS heat, Q is positive If system LOSES heat, Q is negative An analogy which work done on a system (eg lifting a box) increases the mechanical (potential) energy of the system. By analogy, positive work on a system
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 04/23/2011 for the course PHYS 242 taught by Professor Staff during the Spring '08 term at Purdue.

### Page1 / 24

thermal_5_02_08_2011 - The First Law of Thermodynamics...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online