Thermal/Wave Review

Which object has more heat energy?

A. 30 grams of boiling waterB. A 5 kg ice sculpture at 0°C

Which are true?

During a phase change…

A. The temperature will changeB. The entropy of the material will change

C. The internal energy of the material changesD. The kinetic energy of the material changes

E. Heat is either lost or gained

DO SOME MATH

A material has a specific heat of 20 J/gK and a mass of 45 g. It started at 50 °C, and was given 3500 J of heat energy. Assuming no change in phase, what is it’s final temperature?

Relationships

Which of the following have a direct relationship with Heat gained/lost?

A. Change in TemperatureB. MassC. PhaseD. Average Kinetic EnergyE. Specific Heat

BONUS CHANCE

Absolute Zero

Explain to the class the following:1. What is Absolute Zero

2. What is the temperature in K, and C3. Which law of thermodynamics defines it

Heat transfer

Identify the type of heat transfer that takes place in each of the following:

A. A car’s heater blows hot air from the engineB. A magnifying glass burns up an antC. You burn your mouth while drinking soupD. Wax in a lava lamp expands and rises upE. Food is cooked in an oven (more than one?)

ENTROPY

The second law of thermodynamics says that overall entropy of the universe must always increase. Why then can some things decrease in entropy?

Write an example of a common entropy decrease and why it does/doesn’t violate the 2nd law.

More relationships

Two containers made of the same material gain the same amount of heat energy. One container is 3 times as massive as the other. The smaller container increases temperature by 15 °C. By how much does the other container’s temperature change? Do you have enough information?

MAKE SOME WAVES

Draw the following waves:

A. A bright red lightB. A dim violet light

C. A high-pitched sound

BONUS CHANCE

Imitate the sound from an ambulance approaching and then passing you.

Remember the Doppler effect!

Doppler Effect (continued)

The Doppler Effect also affects light!

If an object is fleeing from you rapidly while emitting light, what will happen to the color of the light?

Quick Calcs

2 minutes for the first calc, then half the time for each one after!

• Find “c”: Q= 20 J, m=5 g, Ti = 30, Tf=40• Find period if 30 waves pass by in 5 seconds.• Find wavelength: v = 30 m/s, f = 15 Hz• Find frequency if period = 40 seconds.• Find wave velocity: λ = 12, f = 10 Hz

Draw the following:

A. A wave being absorbedB. An example of diffraction

C. A light wave reflectedD. A light wave refracted

BONUS CHANCE

Resonance

Without using any words – come up to the front and act out an example of resonance.

More relationships

Which of the following are inversely related:

A. Frequency and wave speedB. Wavelength and Frequency

C. Wavelength and PeriodD. Period and wave speed

E. Temperature and frequency (for sound)F. Frequency and Period

Answers:

1. B2. B,C,E3. 53.8 C4. A, B, D, E5. The lowest theoretical temperature

0 K, -273 C 3rd law of thermodynamics6. Convection, Radiation, Conduction, Convection, All 37. Water Freezing, Even if water freezes the entropy

elsewhere increases as a result

Answers:

8. 5 C, yes9. Large Amplitude, long wavelength

Small amplitude, short wavelengthAreas of compression and rarefaction

10. Start with a high pitch and then drop to a low pitch

11. The light will look more red. (frequency decrease)

12. .4 J/gK, .17 seconds, 2 m, .025 Hz, 120 m/s

Answers

13. See examples in “Wave Comparison Charts” Document

14. An example where an object is forced to vibrate at its natural frequency

15. B, D, F