Thermodynamics – branch of physics concerned with the study of both thermal and mechanical (or dynamical) concepts.

Application: Steam Engines in 1800’s

Adiabatic Example:When a particular piston is released, it expands adiabatically, lifting a weight. The internal energy goes down 10 J. How high was the weight lifted?

Isobaric Example:Air in a balloon heats up and expands from 0.1 m3 to 0.2 m3 at atmospheric pressure. How much work is done on the gas?

Isovolumetric Example:10 g of steam is heated 5°C in a closed container. What is the change in the internal energy of the steam?

Isothermal Example:An ideal gas expands from 2.0 m3 to 3.0 m3 at constant temperature. What is the work done by the gas?

4-Stroke Engine:https://www.youtube.com/watch?v=SYd40qWQ9Bc

Different ways that compressions, expansions, etc. can occur:• Adiabatic• Isothermal• ….

What happens to the temperature of the air that is let out of a car tire?

1. it increases.2. it decreases. 3. it remains the same.

Consider a cylinder divided into two parts by a membrane. On one side of the membrane is a gas at a pressure P, and temperature T. The other side is evacuated. If the membrane vanished, the gas would rush to fill the evacuated side, and its temperature would

1. increase.2. decrease. 3. remain the same.

If a system does work adiabatically, 1. the temperature stays the same.2. the internal energy stays the same.3. the internal energy decreases.4. the internal energy increases.5. none of the above.

A cylinder and piston contains a gas that is made to expand from A to B at a constant temperature as shown below.

A

B

P

V

This process is1. adiabatic and heat leaves the gas.2. isothermal and heat enters the gas.3. adiabatic and heat enters the gas.4. isothermal and heat leaves the gas.5. none of these.

A gas in a piston is compressed adiabatically by a force of 500 N acting through a distance of 5 cm. The net change in the internal energy of the gas is

1. +500 J.2. +25 J.3. -500 J.4. -25 J.5. none of the above.

An adiabatic process is one that occurs without changes in

1. Pressure2. Density3. Temperature4. Energy by heat

If a gas is compressed isothermally, which of the following statements is true?

1. Energy is transferred into the gas by heat. 2. No work is done on the gas. 3. The temperature of the gas increases. 4. The internal energy of the gas remains

constant. 5. None of those statements is true.

A piston is quickly pushed downward. This process is best described by:

1. Adiabatic2. Isothermal3. Constant energy4. None of the above5. Two of the above

One mole of an ideal gas is placed in a copper cylinder and piston setup. The piston is slowly lowered until the pressure has doubled. This process is best described as:

1. Adiabatic2. Isothermal3. Constant energy4. None of the above5. Two of the above

Estimate the total work by a system taken around the cycle shown in the figure. Does the system have to be an ideal gas?

Conduction Example:An air-bake cookie sheet consists of a top and bottom aluminum sheet, separated by a thin layer of air. The aluminum sheets are both 3 mm thick and they are separated by 5mm. The cookie sheet has a length and width of 20 cm. If place on a stove at 200°C, how much energy reaches the top of the cookie sheet each minute?

kAl = 238 W/m°CKair = 0.0234 W/m°C

Conduction Example:One side of a 0.1 m thick aluminum block rests on a 20°C table. A piece of glass is placed on top of the aluminum to separate it from an object held at 2000°C. If aluminum melts at 660°C, how thick does the glass need to be to keep the aluminum from melting?

kAl = 238 W/m°CKglass = 0.8 W/m°C

Radiation Example:A ball (r = 1 cm, e = 0.4) initially at 300 K is suspended in a vacuum chamber that is kept at 77 K by liquid nitrogen. What is the initial rate of energy lost by the ball?

Two brick walls have the same surface area, but wall A is twice as thick as wall B. If the temperature difference between the sides of wall A is twice the temperature difference between the sides of wall B, the rate of heat transfer is

1. greater for wall A.2. greater for wall B.3. the same for walls A and B.

The purpose of a cover on a soup kettle is to

1. increase conductivity.2. decrease convection.3. increase radiation.4. decrease conduction.5. none of these.

A moistened finger will stick to a lamppost on a very cold day, but it won’t stick to wood. The reason has to do with

1. the difference in specific heats.2. the difference in thermal conductivity.3. the difference in temperatures.4. the latent heat of fusion.5. none of the above.

The figure shows a test tube containing water and some ice (held down by a weight). As shown, the water at the top is boiling. Is that possible, and, if so, why?

1. yes, because the water has a high heat of vaporization.2. no, because the water has a low specific heat capacity.3. yes, because the water has a low thermal conductivity.4. no, because the water has a low heat of fusion.5. none of these.

Water

Ice

Suppose you pour a cup of hot coffee and the phone rings so you can’t drink it. To keep it hot as long as possible,

1. add the cool milk and sugar immediately.2. don’t add the cool milk and sugar until you are ready to drink it.

For ease of use and safety, a fireplace poker should be made from a material

1. with high specific heat and high thermal conductivity.2. with low specific heat and low thermal conductivity.3. with low specific heat and high thermal conductivity.4. with high specific heat and low thermal conductivity.

Why does ice form on a bridge before it does on the rest of the road?

1. conduction.2. convection.3. radiation.4. none of these, because the ice freezes without changing temperature.

Problem:A 2-mol sample of helium gas initially at 300 K and 0.400 atm is compressed isothermally to 1.20 atm. Noting that the helium behaves as an ideal gas, find:a) The final volume of gas.b) The work done on the gas.c) The energy transferred by heat.