Thermodynamics B/C

[mjcox2000]

I'm confused how the reservoirs could reach equilibrium? The Carnot cycle assumes that the reservoirs will never change temperature.

The Carnot cycle doesn’t require constant-temperature reservoirs.

Hint (Click to Show Hidden Text)

The Carnot efficiency equation predicts the instantaneous efficiency. Try integrating.

Answers (assuming I used that hint right): (Click to Show Hidden Text)

1. 252 K
2. 5920 J
3. 2880 J
4. 48.6 %

Correct on parts 1, 2, and 3.

Correction for part 4 (Click to Show Hidden Text)

It should be 51.4% — I assume you found the percentage of wasted energy, not usable energy.

Your turn!

[wec01]

Suppose you had a cylinder with a piston in it. Describe how you would cause the system to undergo:
1. adiabatic expansion
2. isothermal expansion
3. isobaric expansion

[mjcox2000]

Suppose you had a cylinder with a piston in it. Describe how you would cause the system to undergo:
1. adiabatic expansion
2. isothermal expansion
3. isobaric expansion

Answer (Click to Show Hidden Text)

1. Quickly pull on the piston
2. Submerge the cylinder in a constant-temperature water bath and slowly pull on the piston
3. Heat the cylinder and don’t touch the piston

[wec01]

Suppose you had a cylinder with a piston in it. Describe how you would cause the system to undergo:
1. adiabatic expansion
2. isothermal expansion
3. isobaric expansion

Answer (Click to Show Hidden Text)

1. Quickly pull on the piston
2. Submerge the cylinder in a constant-temperature water bath and slowly pull on the piston
3. Heat the cylinder and don’t touch the piston

Yep, your turn

[mjcox2000]

A sample of air starts at STP. Then, a sound source emitting a 10kHz sine wave is placed in the sample of air. At a certain point P at a given distance from the sound source, the RMS sound pressure level is 100 dB. Assuming air behaves adiabatically when sound travels through it and there are no frictional losses, what is the minimum and maximum temperature at point P?

[wec01]

A sample of air starts at STP. Then, a sound source emitting a 10kHz sine wave is placed in the sample of air. At a certain point P at a given distance from the sound source, the RMS sound pressure level is 100 dB. Assuming air behaves adiabatically when sound travels through it and there are no frictional losses, what is the minimum and maximum temperature at point P?

Not sure if I approached this right, but I got (Click to Show Hidden Text)

[math]\pm 9.2 * 10^{-3} ^{\circ} C[/math]

[wec01]

A sample of air starts at STP. Then, a sound source emitting a 10kHz sine wave is placed in the sample of air. At a certain point P at a given distance from the sound source, the RMS sound pressure level is 100 dB. Assuming air behaves adiabatically when sound travels through it and there are no frictional losses, what is the minimum and maximum temperature at point P?

Not sure if I approached this right, but I got (Click to Show Hidden Text)

[math]\pm 9.2 * 10^{-3} ^{\circ} C[/math]

Oops, I see an error in my work; working on fixing it

[wec01]

A sample of air starts at STP. Then, a sound source emitting a 10kHz sine wave is placed in the sample of air. At a certain point P at a given distance from the sound source, the RMS sound pressure level is 100 dB. Assuming air behaves adiabatically when sound travels through it and there are no frictional losses, what is the minimum and maximum temperature at point P?

Not sure if I approached this right, but I got (Click to Show Hidden Text)

[math]\pm 9.2 * 10^{-3} ^{\circ} C[/math]

Oops, I see an error in my work; working on fixing it

Still very unsure about my answer but I got (Click to Show Hidden Text)

[math]\pm 7.6 * 10^{-3} ^{\circ} C[/math]