What is Reversible: Definition and 247 Discussions
Reversible computing is a model of computation where the computational process to some extent is time-reversible. In a model of computation that uses deterministic transitions from one state of the abstract machine to another, a necessary condition for reversibility is that the relation of the mapping from states to their successors must be one-to-one. Reversible computing is a form of unconventional computing.
Due to the unitarity of quantum mechanics, quantum circuits are usually reversible.
I want to consider all possible reversible cycles that consist of an isothermal expansion at TH and an isothermal compression at TC.
The other two processes can be isochoric, isobaric, adiabatic or anything else, but they should never leave the temperature range between the two isotherms.
I also...
Can someone explain me what does the underlined part of the following passage mean?
"The reversible operation of a fuel cell implies that the external circuit exactly balances its emf, with the result that its current output is negligible. In actual operation under reasonable load, internal...
I came across the following statement from the book Physics for Engineering and Science (Schaum's Outline Series).
I cannot seem to find a satisfactory answer to the questions.
Is the statement in above screenshot talking about entropy change the statement of Second Law of Thermodynamics or is...
As far as I learned, the following statements should be correct (for closed systems, no chemical reactions), irrespective whether the process is reversible or irreversible (since S and V are state variables):
dU=TdS−pdV
dU=dQ+dW
Does this imply, that the statement:
dU≤TdS−pdV
is wrong?
This...
Has any of the reversible extensions of the elementary one-dimensional cellular automata described by Wolfram in NKS (e.g. Rule 37R) been shown to be computationally universal (like Rule 110)? If so, please give me links. Otherwise, could this be the case? Or is there a proof that no nR can be...
I have a reversible electric motor that operates an automatic skylight, vintage 1985. I'm trying to figure out how it is supposed to work, but I don't recognize the rectangular gray components that are secured to the motor case with a length of plastic zip-tie. What might they be and how would...
If light at a known polarization goes through a beam splitting polarizer that changes the light's polarization and then goes through the reverse orientation of that polarizer it will exit with the same polarization that it entered with. See the following picture:
If the polarization state...
Hi,
reading the interesting Reversible vs Irreversible Gas Compression and Expansion Work insight by @Chestermiller I would like to ask for clarification on some points.
In the second bullet at the beginning
my understanding is as follows: consider an ideal gas contained in a cylinder...
The question is given in 3 parts.
For first part, process is isochoric so Work done=0. We know here that at end of the process (a), T2=T1 while V remains constant (we can take it as V1) so P2=2P1.
For second part, process is isothermal so T is constant. At end of process we reach P1 again from...
In the book for our thermodynamics, it states that a process that is internally reversible and adiabatic, has to be isentropic, but an isentropic process doesn't have to be reversible and adiabatic. I don't really understand this. I always thought isentropic and reversible mean the same thing...
We know that
$$dU=\delta Q + \delta W$$
$$dU = TdS - pdV$$
So from this:
$$dS = \frac{1}{T}dU + \frac{1}{T}pdV \ (*)$$
For an ideal gas:
$$dU = \frac{3}{2}nkdT$$
Plugging that into (*) and also from ##p=\frac{nRT}{V}## we get:
$$S = \frac{3}{2}nk \int^{T_2}_{T_1} \frac{1}{T}dT +...
i have tried to understand Feynman's words i think i finally understands what he means by "we must add a little extra to get it to run"
he refers to the "inversion" of the process, that's when we need to add extra work (lifting up a little mass)
please correct me if I am wrong, this is something...
Hi,
A quick question on a conundrum I seem to have encountered. My main question is: why is it wrong to use the formula above instead of the SFEE approach?
My approach:
Use the formula:
$$ w = \frac{R}{1-n} (T_2 - T_1) $$
From the data book, ## R = 0.287 ## kJ/kg K and ## n = \gamma = 1.4 ##...
I am not able to follow the derivation of work done in a reversible and irreversible process as I don't get why the work done should be different in the two processes.
a reversible process is said to be a process that occurs infinitesimally slowly and an irreversible process goes from initial to...
Hi all. I am referencing the example given in Halliday and Resnick, Chapter 20, Section 1, Subsection "Change in Entropy". The above picture is graph of the free expansion of a gas into a volume that is double its original volume. I n a free expansion there is no heat transfer, the pressure...
So we know that every reversible engine working between the same temperatures will have the same efficiency(the same as Carnot engine). So let's consider for example reversible Otto cycle. So as you can see on the picture it is operating between ##T_1## and ##T_3##, so I was thinking that it...
My question is: Do ALL the reversible process need to be composed of ONLY isothermal and adiabatic transformations? Carnot cycle satisfy this, but what other cycle would be also reversible?
I know that for a process to be reverisble it has to be almost-static, have no dissipative force, and no...
Attempt at A Solution
Problem 1
Reversible Process - A cylinder of ideal gas at pressure P is in mechanical equilibrium with a piston of area A driven by a spring of force F = PA and thermal equilibrium with a reservoir of temperature T. The piston is moved a small distance dx toward the...
By reversibility, if we turn the direction of the light propagation by 180 degrees, then the new propagation path follows the old propagation path. I suspect that when there is diffraction, the light propagation is not reversible?
I started reading "Feyman Lectures on physics" and stuck on his explanation about reversible and irreversible machines. I've tried to read other answers to this question, but I couldn't get the point. Here is the first thing:
"If, when we have lifted and lowered a lot of weights and restored...
My attempt:
I though :
ΔQ_w= 1*4200 * (-100) J=-420000J
Q_ice=334000*m_ice = ΔQ_w
But it was totaly wrong!
The solution showed :
Because the heat engine is reversible the efficiency η = 1- (T_cold / T)
T_cold is always 273 K while the hot temperature changes from 373 K to 273 K during this...
Hi,
I was revisiting my (high school level) understanding of thermodynamic cycles and I think I still have some doubts. Last year and more recently I posted a few questions which surely helped me, but I think I need more clarifications.
In a nutshell, what I'd like to know is the following...
I am trying to investigate my doubts that reversible operations can model (or at least mimic) information copy process.
For simple model I take two numbers ##A \neq B##. Now I can't copy value of A into B without erasing (irreversibly) value of B. However I can use transformation that replaces...
The refrigeration process is used in air conditioning to dehumidify and control temperatures in homes and buildings. The heating industry preceded the air conditioning business and many evaporator coils were placed on top of furnaces to create split systems and utilize existing ductwork. The...
Hi,
consider an adiabatic irreversible process carrying a thermodynamic system from initial state A to final state B: this process is accompanied by a positive change in system entropy (call it ##S_g##). Then consider a reversible process between the same initial and final system state. Such...
Consider a reaction:
H2+CuCl2= Cu+2HCl
This is a substitution reaction.But is this may not be a reversible reaction since Cu is less active than .So Cu can't substitute H from HCl and make a backward reaction.Is my thinking right?
Hi all, I have been having some issues trying to show that a reversible expansion of gas does not create new entropy. Assistance is greatly appreciated!
So suppose that a gas expands reversibly as shown below at fixed temperature
At fixed temperature, internal energy doesn't change so...
Homework Statement
2.Relevant equations[/B]The Attempt at a Solution
How does a reversible process in the universe imply the entropy doesn't increase? I understand that the change of entropy in a closed reversible cycle is 0 in the system, but I don't get why a not closed reversible process...
Homework Statement
Derive an expression for the change of temperature of a solid material that is compressed adiabatically and reversible in terms of physical quantities.
(The second part of this problem is: The pressure on a block of iron is increased by 1000 atm adiabatically and...
Hello,
I am trying to figure out where my reasoning falls apart in this thought experiment:
To determine if a process "A" is reversible (or at the very least internally reversible), I try to picture a reversible process "B" that involves only heat transfer and links the same two endpoints that...
Hello,
I am encountering some confusion understanding the difference in working with reversible and irreversible processes in thermodynamics. Let's say I have a process where an ideal gas at a certain starting temperature ##T_i## expands from volume ##V_i## to ##V_f##. The temperature of the...
Reversible computation is a somewhat well-known topic. (Quantum computers, for instance, must use reversible gates).
Apparently, though, quantum measurements can be reversible too. This also means you could recover the original state by “unmeasuring” the system. Imagine being able to “see” a...
Greetings,
I have begun reading the Feynman Lectures to repeat the most important ideas from my undergraduate studies and to improve my intuitive understanding of physics.
In one of the first chapters, the one about the conservation of energy, he demonstrates that the conservation of energy is...
Is the photoelectric effect in a photocell reversible? Suppose both the cathode and the anode of a photocell are from cesium. The anode and the cathode are externally (outside the photocell) connected by a copper wire. Cesium has a threshold frequency of 470 THz. The cathode is illuminated with...
Here is the code you input into matlab. Aini etc, are the initial values of the population densities. A for predator, B for Prey.
% example for ODE and Gillespie
% one reversible reaction
b1 = .033;
bo = .00047;
a1 = .0022;
ao = .00055;
Aini = 5168;
Bini = 34;
%% Basic ODE simulation...
Homework Statement
How do we know that an adiabatic process is reversible , while isothermal process is not?
Do we have to calculate the entropy change of the process or we have to check experimentally whether the system is in eqbm at infinitesimal time interval( but this seems impossible)...
Does this mean that in reversible process\ quasistatic process, the energy is not lost as heat and the process in which the energy is not lost as heat is known as reversible process\quasistatic process?
I want to know why we want to have reversible \ quasistatic process.
Homework Statement
2kgs (total mass) of steam goes through a revesible isothermal expansion at 500 degrees celcius. During the expansion the pressure drops from 300 kpa to 200 kpa.
What is the heat absorbed by the steam during this process?
Homework Equations
U=W and W=nrt ln(v2/v1)
The...
I am no able to understand the reasoning of Feynman in deducing that it is impossible to build a machine that will lift a weight higher than it will be lifted by a reversible machine. I am also not able to understand what reversible machine is. So, please help me.
Homework Statement
Air enters a compressor at 100 [Kpa] and 10 [c], the air leave the compressor at 12[Mpa]
the isentropic efficiency η is 87%, calculate:
work done
reversible work
irreversibility
Homework Equations
[/B]
T2=T1(P2/P1)(1.4-1)/1.4
W = (Cp(T2-T1))/η
Wrev=Δh - T0Δs
Δs =...
Can someone explain to me what a reversible process means, because I am not sure I really understand. Intuitively it should be a process that should work both ways, but I am not sure I understand how it is related to entropy (the change of entropy should be 0, but I am not sure I understand...
Okay...I read that the decomposition of water is a reversible reaction (because the constituents can react to form water and water can decompose to form constituents)...This lead me to another thought that almost all compounds can be decomposed (although it is true that their conditions for...
Can someone explain what it means for a fluid flow to be reversible and how this relates to Reynolds number, both intuitively and mathematically?
Thanks!
Homework Statement
an Ideal gas at T = 70 C and 1 bar undergoes following reversible
processes:
a: Adiabatically compressed to 150 C
b: then, cooled from 150 to 70 C at constant pressure
c: finally, expanded isothermally to the original state (T=70 C and P = 1 bar)
Homework Equations...
Hello! I have this GRE question:
In process 1, a monoatomic ideal gas is heated from temperature T to temperature 2T reversibly and at constant temperature. In process 2, a monoatomic ideal gas freely expands from V to 2V. Which is the correct relationship between the change in entropy ##\Delta...
Hello,
I am currently trying to get my head around the concept of entropy. One way to understand it is that it can be related to the amount of available energy levels in a system.
From what I read, the availability of energy levels in a system:
1) increase with an increase in the system...
Is there a definition for "reversible process" that applies to mechanical systems (such as a block sliding down a frictionless inclined plane) that is distinct from the definition of "reversible process" in thermodynamics?
If we apply the thermodynamic definition of "reversible process" to...
Homework Statement
Calculate the change in internal energy of an ideal gas the expands reverisbly and adiabatically from ##v_i## to ##v_f##
Homework Equations
##pV^{\gamma} = constant ##*, where ##\gamma=\frac{c_p}{c_v}##
for a reversible adiabatic.
##E=\alpha p V##, ##\alpha## a constant...