Go Back   Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Thermodynamics and Fluid Mechanics Thermodynamics and Fluid Mechanics Physics Help Forum

Like Tree4Likes
  • 1 Post By HallsofIvy
  • 1 Post By HallsofIvy
  • 2 Post By Woody
Reply
 
LinkBack Thread Tools Display Modes
Old Jan 1st 2019, 05:51 AM   #1
Junior Member
 
Join Date: Dec 2018
Location: The 'Milky Way' Galaxy
Posts: 13
Question efficiency proof

How is this proved?

Efficiency of a battery is:

|delta G| *100
----------------
|delta H|

where delta G-change in gibbs free energy
delta H-change in enthalpy.
mak29 is offline   Reply With Quote
Old Jan 1st 2019, 09:53 AM   #2
Senior Member
 
Join Date: Aug 2010
Posts: 389
There is no "proof" it is a definition!
topsquark likes this.
HallsofIvy is offline   Reply With Quote
Old Jan 1st 2019, 10:09 AM   #3
Junior Member
 
Join Date: Dec 2018
Location: The 'Milky Way' Galaxy
Posts: 13
Somehow it is concluded.
I just want to know how.
mak29 is offline   Reply With Quote
Old Jan 2nd 2019, 04:02 AM   #4
Senior Member
 
Join Date: Aug 2010
Posts: 389
Then what do you mean by "efficiency of a battery"? What definition are you using?
topsquark likes this.
HallsofIvy is offline   Reply With Quote
Old Jan 2nd 2019, 11:45 AM   #5
Forum Admin
 
topsquark's Avatar
 
Join Date: Apr 2008
Location: On the dance floor, baby!
Posts: 2,527
Typically an efficiency is defined based either on the work done by the system divided by work done on the system. This usually involves the entropy change of the system or, in more practical to measure terms, the temperature change in the system. But, as HallsofIvy mentioned, different definitions are simpler to employ for different systems.

Take a look at the entropy. That's all I can think of to start with.

-Dan
__________________
Do not meddle in the affairs of dragons for you are crunchy and taste good with ketchup.

See the forum rules here.
topsquark is offline   Reply With Quote
Old Jan 4th 2019, 10:30 AM   #6
Senior Member
 
Woody's Avatar
 
Join Date: Jun 2016
Location: England
Posts: 750
If I ever knew the terms you use in your efficiency equation, I have long since forgotten.
(I might be able to hear a vague tinkle of the recognition bell, but I'm not sure)

However, efficiency is essentially
How much can actually be got out of the system (the battery in this case)
divided by how much could ideally be got out of the system.

Ideally (100% efficiency) you would get everything out that you put in.
For a battery you put in the chemical energy, you get out electrical energy.

How do the terms in your equation relate to these quantities?

Note that I suspect the "100" in the equation is to present the efficiency as a percentage (rather than as a number between 0 and 1).
topsquark and mak29 like this.
__________________
~\o/~
Woody is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Thermodynamics and Fluid Mechanics

Tags
efficiency, proof



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Proof of singularity. avito009 Philosophy of Physics 2 Jan 20th 2018 04:49 PM
Classical proof of g-factor Torgny Advanced Electricity and Magnetism 2 Jul 20th 2017 05:45 AM
proof V and T as forces in spontanity Torgny Advanced Thermodynamics 0 Sep 6th 2016 01:40 PM
projectile trajectory proof helloworld101 Kinematics and Dynamics 8 Nov 20th 2009 09:17 AM
Newton/Kinematic Proof mattc Kinematics and Dynamics 1 Oct 21st 2009 12:14 AM


Facebook Twitter Google+ RSS Feed