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Heat supply to a system

  1. Sep 2, 2018 #1
    My book states that
    Heat and work represent energy in transit. The state of the system undergoes a change after heat is supplied to it and before work is extracted from it because energy gets stored in it.
    My doubt is here that ,heat has been transferred to the system and it says heat is energy in transit and can't be stored but then it says system undergoes change cause energy is stored in it . This makes me confused. Please someone make me understand the concept behind this ,I know I have a big misconception .
  2. jcsd
  3. Sep 2, 2018 #2
    Take capicitors as example, electricty is energy and it can't be stored, but when we charge a capicitor, it can "store" the energy by gathering the electrons on both sides of it's pannel to one side using electricity, which creates a charge.Now this system changed it's state from a lower energy level(electrons on both panels) to a higher energy level(electrons on one side of the panel).The process is inversed when releasing the charge by touch both ends of the capicitor, now this charge is converted back to energy(which can't be stored)which will immediately be used up or converted again into another type of energy,depending what circuit you connect the capicitor to, this may result to
    • heat, if it's connected to a short circuit
    • light, if connected of a led
    • kinetic energy, if connected to a motor
    Hope this solved your problem.
  4. Sep 2, 2018 #3


    Staff: Mentor

    I think your book is a bit sloppy with use of the word heat. It should have said Work and the flow of heat represent energy in transit.
  5. Sep 2, 2018 #4
    You are aware of the difference between heat, work, and internal energy, correct? In the example you cite, heat is transferred to the system, and, as a result, the internal energy of the system increases.
  6. Sep 2, 2018 #5
    My understanding of heat ,work amd internal energy are:
    Heat is a form of energy in transit due to temperature difference
    Work is said to be done when a force acts to displace a body in the direction of force
    Internal energy is the energy due to the molecules of the system
  7. Sep 2, 2018 #6
    Then what is your problem?
  8. Sep 2, 2018 #7
    The statement of the book that I asked
  9. Sep 2, 2018 #8
    What do the works "In the example you cite, heat is transferred to the system, and, as a result, the internal energy of the system increases." from my previous post mean to you?
  10. Sep 2, 2018 #9
    Some kind of mechanical work I guess , like moving a piston in a cylinder.
  11. Sep 2, 2018 #10
    I have no idea how you could interpret it that way. It means that the heat transferred to the system causes the internal energy of the system to increase.
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