A-LEVEL PHYSICS: 11.2.12: Reversed Heat Engines (SaveMyExams)

Question 1

reversed heat engine:

Answer 1

transfers heat energy from a sink (TC) to source (TH) via an input of work

Question 2

why does work need to be done in reversed heat engines?

Answer 2

bc heat energy Q naturally flows from hot to cold (source to sink)
whereas in reversed heat engine, Q flows cold to hot (sink to source) ∴ work needs to be done

Question 3

reversed heat engines are used for: (2)

Answer 3

-refrigerators / air-con

-heat pumps (engine used to heat a building)

Question 4

heat pump:

Answer 4

an engine used to heat a building

provides as much energy as possible to the hot space per joule of work done

Question 5

source-sink diagram for reversed heat engine:

Answer 5

source (TH)
↑ (QH)
↑
← W input
↑
↑ (QC)
↑
sink (TC)

Question 6

in reversed heat engines, QH will always be ___ then QC for this to work.
applying the first law of thermodynamics means that:

Answer 6

greater

QH = QC + W

Question 7

a refrigerator extracts as much energy as possible from the ___ space per joule of work done

Answer 7

cold

Question 8

a refrigerator wants to stay ___, so it is taking the ___ out of the system

Answer 8

cold, heat

Question 9

the ___ of a fridge is the ___ space & the ___ is the ___ space

Answer 9

inside, cold, outside, hot