reversible

Examples of reversible in the following topics:

• A Physical Aside: Einstein coefficients

  • Because quantum mechanics for the most part is time reversible, the cross-section for the forward and reverse reactions are related.

• Carnot Cycles

  • The Carnot cycle is the most efficient cyclical process possible and uses only reversible processes through its cycle.
  • What is crucial to the Carnot cycle is that only reversible processes are used.
  • Obviously, then, reversible processes are superior.
  • Recall that both isothermal and adiabatic processes are, in principle, reversible .
  • PV diagram for a Carnot cycle, employing only reversible isothermal and adiabatic processes.

• What is Entropy?

  • We noted that for a Carnot cycle, and hence for any reversible processes, Qc/Qh=Tc/Th.
  • Rearranging terms yields $\frac{Q_c}{T_c} = \frac{Q_h}{T_h}$ for any reversible process.
  • This ratio of Q/T is defined to be the change in entropy ΔS for a reversible process,
  • PV diagram for a Carnot cycle, employing only reversible isothermal and adiabatic processes.
  • Calculate the total change in entropy for a system in a reversible process

• The Second Law

  • If the process can go in only one direction, then the reverse path differs fundamentally and the process cannot be reversible.
  • Furthermore, mechanical energy, such as kinetic energy, can be completely converted to thermal energy by friction, but the reverse is impossible.
  • The Second Law of Thermodynamics(first expression): Heat transfer occurs spontaneously from higher- to lower-temperature bodies but never spontaneously in the reverse direction.
  • The reverse process is impossible.

• Helical Motion

  • If field strength increases in the direction of motion, the field will exert a force to slow the charges (and even reverse their direction), forming a kind of magnetic mirror.
  • This force slows the motion along the field line and here reverses it, forming a "magnetic mirror. "

• Charging a Battery: EMFs in Series and Parallel

  • When it is reversed, it produces an emf that opposes the other, and results in a difference between the two voltage sources .
  • The charger must have a larger emf than the battery to reverse current through it.

• Stastical Interpretation of Entropy

  • The most disorderly possibilities are 3 heads and 2 tails and its reverse.
  • (They are the least structured. ) The most disorderly possibilities are also the most likely, with 20 out of 32 possibilities for the 3 heads and 2 tails and its reverse.
  • The reverse can happen, but it is unlikely.

• Geomagnetism

  • These events are called geomagnetic reversals.
  • Reversals occur at apparently random intervals ranging from less than 0.1 million years to as much as 50 million years.
  • The most recent such event, called the Brunhes-Matuyama reversal, occurred about 780,000 years ago.

• Photon Interactions and Pair Production

  • The reverse process is also possible.

• NMR and MRIs

  • This electromagnetic field has just the right frequency (known as the resonance frequency) to become absorbed and then reverse the rotation of the hydrogen protons in the magnetic field.