January 7 AP Physics

IN A gas follows the cycles shown. How much work is done?

Objective: To study cycles in thermodynamics. Success Criteria: To be able to calculate the work done in a thermodynamic cycle.

Homework check 2, 5, 6, 10

PV diagram

PV diagram-holding pressure constant

PV diagram-holding volume constant

PV diagram-holding temperature constant

Work and PV diagrams (quick quiz 12.1) Put these in order: most negative work to most positive work.

First law of Thermodynamics ΔU = Q + W

Isobaric (pressure constant) ΔU = Q + W

Isovolumetric (volume constant) ΔU = Q

Isothermal (temperature constant) ΔU = 0 Therefore Q = W

Adiabatic (isolated system) ΔU = W

Work in thermodynamic processes W=FΔd W=PAΔd W= - PΔV

Processconditions first law Isobaricboth temp ΔU=Q+W and volume change Isovolumetricno workΔV=0 so W=0 so ΔU=Q Isothermalno change ΔU=Q+W=0 in T or U so Q= - W Adiabaticno energyQ=0 transfer asso ΔU=W heat

PV diagrams and thermodynamic processes (quick quiz 12.2) Identify the paths

PV diagram of a cycle

Steam engine

Newcome Steam engine

Problem 4

Otto cycle Otto Engine

Diesel cycle Diesel Engine

Efficiency of an engine Work out Energy in e = W Q H

Sadi Carnot Reflections on the Motive Power of Fire Efficiency of a heat engine Theoretical maximum Began the understanding that became the second law of thermodynamics. –entropy

Carnot cycle

The Carnot Engine

Carnot Engine No real engine operating between two energy reservoirs can be more efficient than a Carnot engine operating between the same two reservoirs. e c = T H -T C T H

Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are: a) T h =1000 K T c =700 K b) T h =800 KT c =500 K c) T h =600 KT c =300 K Rank the engines in order of their theoretical maximum efficiency.

Second Law of Thermodynamics No heat engine operating in a cycle can absorb energy from a reservoir and use it entirely for the performance of an equal amount of work. You cant have a totally efficient engine. In any closed system, entropy always increases.

Entropy

Out: Which of these processes are isothermal, isovolumetric, or adiabatic: a)A tire being rapidly inflated b)A tire expanding gradually at a constant temperature c)A steel tank of gas being heated