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

Reply
 
LinkBack Thread Tools Display Modes
Old Oct 6th 2013, 02:59 AM   #1
Junior Member
 
Join Date: Oct 2013
Posts: 1
Question regarding Heating effect of electric current and mechanical equiv. of heat



Well, I've encountered this problem as I was studying for my exams.
Basically, it's asking me to solve for the "mechanical equivalent of heat". I've scoured the internet for information regarding it, basically what I'm getting is that it's something like a conversion factor. So that makes me confused as to why it's making me look for something like that.

This set-up is quite familiar to me though, as I've encountered it in calorimetry and the concept where Q=mc(delta T) is involved.

I've also read some history on the mech equiv of heat, stating that it was some experimentally acquired constant, that's where i base my solutions from. I've also read that the values ranged from around 4.15 to 4.22.

So here's my take:
(from the heating effect off electric current)
H=VIt
H=V^2t/R (from's ohm's law)
H=(110^2*)(75)/(55)
H=16,500 J

(from that concept where Q=mc dT is involved)
Q1 = (153)(1)(35-10)
Q1 = 3825 cal

Q2 = (60)(0.1)(35-10)
Q2=150
Qtotal = 3975

(having prior knolwedge that the currently accepted value for J is around 4.19, I tried dividing the two answers)

J = 16,500J/3975Cal
J = 4.15 J/Cal
Am I spot on?
If I'm right, the question is like asking me to confirm the value of the constant am I right?

I'm still a bit confused about the "mech. equiv. of heat", is it just a conversion factor? Is there something more?
physics345671 is offline   Reply With Quote
Old Oct 6th 2013, 04:40 AM   #2
Physics Team
 
ChipB's Avatar
 
Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,352
I think you have it right. The notion of "mechanical equivalent of heat" dates from the early days of advances in thermodynamics in the 1850's, and came about with the realization that mechanical energy and heat are both two aspects of the same thing, and that it's really about conservation of energy and the specific heat of water. The notion that heat in calories is equivalent to mechanical energy in joules took some time to be accepted.
ChipB is offline   Reply With Quote
Reply

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

Tags
current, effect, electric, equiv, heat, heating, mechanical, question



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Effect of electric potentials on electromagnetic waves NathanW Advanced Electricity and Magnetism 0 May 26th 2016 10:34 AM
Industrial water heating / heat loss SwireWS Advanced Thermodynamics 2 Oct 31st 2015 04:49 AM
Electric Current draught Electricity and Magnetism 3 Oct 24th 2010 01:39 AM
Converting total heat in mechanical work. george Advanced Thermodynamics 19 Jul 17th 2009 01:08 PM


Facebook Twitter Google+ RSS Feed