january 7 ap physics. in a gas follows the cycles shown. how much work is done?

January 7AP 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

Process conditions first law

Isobaric both temp ΔU=Q+Wand volume change

Isovolumetric no work ΔV=0 so W=0so ΔU=Q

Isothermal no change ΔU=Q+W=0

in T or U so Q= - WAdiabatic no energy Q=0

transfer as so ΔU=Wheat

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

QH

Sadi Carnot1796-1832

• 1824-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

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.

ec= TH-TC

TH

Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are:

a) Th=1000 K Tc=700 K

b) Th=800 K Tc=500 K

c) Th=600 K Tc=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 can’t 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