This shows you the differences between two versions of the page.
| Both sides previous revision Previous revision Next revision | Previous revisionLast revisionBoth sides next revision |
| 183_notes:heat [2021/04/15 17:09] – [Two blocks in contact] stumptyl | 183_notes:heat [2021/06/02 23:05] – [Q Can Be Positive(+) or Negative(-)] stumptyl |
|---|
| $$\Delta E_{sys} = W_{surr} + Q $$ | $$\Delta E_{sys} = W_{surr} + Q $$ |
| |
| ==== Q can be positive or negative ==== | ==== Q Can Be Positive(+) or Negative(-) ==== |
| |
| The microscopic work ($Q$) can be positive or negative, just as [[183_notes:work#work_can_be_positive_negative_or_zero|you found with macroscopic work]]. But, the difference here depends on the choice of system and not the direction of forces and displacements. | The microscopic work ($Q$) can be positive or negative, just as [[183_notes:work#work_can_be_positive_negative_or_zero|you found with macroscopic work]]. But, the difference here depends on the choice of system and not the direction of forces and displacements. |
| If, instead, the system under consideration is cooler than its surroundings, then it will decrease the thermal energy of its surroundings (lower the temperature of the surroundings). At the same time, the temperature of the system itself will rise. Thus, the total energy of the system will increase ($\Delta E_{sys} > 0$). Hence, the sign of $Q$ is positive. Energy has been transferred into the system. This is represented by the blue block below. | If, instead, the system under consideration is cooler than its surroundings, then it will decrease the thermal energy of its surroundings (lower the temperature of the surroundings). At the same time, the temperature of the system itself will rise. Thus, the total energy of the system will increase ($\Delta E_{sys} > 0$). Hence, the sign of $Q$ is positive. Energy has been transferred into the system. This is represented by the blue block below. |
| |
| {{ 183_notes:heat_exchange.004.png?500 }} | {{ 183_notes:week10heattransfer2.png?500 }} |
| |
| ==== Examples ==== | ==== Examples ==== |