A block of copper (SL model) is subjected to a change of state. The process is isentropic (that is, entropy does not change. Which of the following statements best describe the change of state. C. u is constant E. h is constant A. No change at all B. T is constant D. B and C


Answer 1

To develop this problem it is necessary to apply the definitions of entropy change within the bodies

The change of entropy in copper would be defined as


Q= Heat exchange

T = Temperature

For an incompressible substance, the change in the heat exchange is defined as


m = Mass

c = Specific heat

Replacing in our equation we have that

Since  , then

In this way for the change of enthalpy and internal energy you have to

As , then

Therefore the correct option is A. No change at All

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Define the difference between elastic and plastic deformation in terms of the effect on the crystal lattice structure.



Elastic Deformation:

  • Elastic deformation is due to the elasticity of the body i.e., the deformation disappears on removal of external forces and the lattice regain its original structure.
  • This type of deformation is temporary  in nature.
  • This type of deformation depends mainly on the chemical bonding of the substance.
  • It occurs due to bending or stretching of chemical bond under applied stress where atoms do not slip pass over each other.
  • It is a reversible process.

Plastic Deformation:

  • Plastic deformation is due to the plasticity of the body i,e., the structure can be easily shaped or molded .
  • This type of deformation is permanent  in nature.
  • This type of deformation occurs mainly due to breakage of chemical bonds(limited in number) between constituent atoms.
  • Atoms may slip pass each other causing dislocation of atoms , resulting in permanent deformation even after stress is removed.
  • It is an irreversible process.

The real power delivered by a source to two impedances, ????1=4+????5⁡Ω and ????2=10⁡Ω connected in parallel, is 1000 W. Determine (a) the real power absorbed by each of the impedances and (b) the source current.



The question is incomplete, below is the complete question

"The real power delivered by a source to two impedance, Z1=4+j5⁡Ω and Z2=10⁡Ω connected in parallel, is 1000 W. Determine (a) the real power absorbed by each of the impedances and (b) the source current."


a. 615W, 384.4W

b. 17.4A


To determine the real power absorbed by the impedance, we need to find first the equivalent admittance for each impedance.

recall that the symbol for admittance is Y and express as

Hence for each we have,  

for the second impedance we have

we also determine the voltage cross the impedance,

P=V^2(Y1 +Y2)

The real power in the impedance is calculated as

for the second impedance

b. We determine the equivalent admittance

We convert the equivalent admittance back into the polar form

the source current flows is


Compute the thermal efficiency for an ideal gas turbine cycle that operates with a pressure ratio of 6.75 and uses helium gas.




pressure ratio, = 6.75

Formula used:



= pressure ratio

γ = specific heat ratio of a gas( here, helium gas it is 1.667)


Eqn (1 ) is for thermal efficiency of an ideal gas, using eqn (1), we get

\eta = 1- \frac{1}{2.1469} = 0.5342

percentage thermal efficiency, \eta =53.42%


Ammonia at 20 C with a quality of 50% and a total mass of 2 kg is in a rigid tank with an outlet valve at the bottom. How much saturated liquid can be removed from the tank in an isothermal process until there remains no more liquid?





Through laboratory tests, thermodynamic tables were developed, these allow to know all the thermodynamic properties of a substance (entropy, enthalpy, pressure, specific volume, internal energy etc ..)  

through prior knowledge of two other properties.

Quality is defined as the ratio between the amount of steam and liquid when a fluid is in a state of saturation, this means that since the quality is 50%, 1kg is liquid and 1kg is steam.

then to solve this problem we find the specific volume for ammonia in a saturated liquid state at 20C, and multiply it by mass (1kg)

v(amonia at 20C)=0.001638m^3/kg


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