Midterm Quiz 3: Physics of Energy & Environment-- PHYS 161

16-November-1999

This exam consists of 15 multiple choice questions (worth 2 points each). Please put your name on the Scantron form and indicate your answers to the questions on it. Important formulae and conversion factors can be found on the last page.

1) An insulated flask containing only warm water is shaken vigorously. What happens to the temperature of the water?

A. The temperature decreases because shaking moves the air through the flask, cooling the water.

B. The temperature decreases because energy from the water escapes into the flask or to the air outside.

C. The temperature remains the same because the water is not exposed to another object or air at a different temperature.

D. The temperature remains the same because the flask is insulated.

E. The temperature of the water increases as shaking the water transfers energy to it.

You are doing work on the water and heat energy transfer away from the water is blocked. Ergo, the water's internal energy (and temperature) must increase.

2) A block of wood and a block of metal are at the same temperature. When the blocks feel cold, the metal feels colder than the wood; when the blocks feel hot, the metal feels hotter than the wood. At what temperature would the blocks feel as hot or as cold as each other?

A. They feel the same when they are both at the temperature of the surroundings.

B. They feel the same when they are both at your body temperature.

C. For the blocks to feel the same, the metal would have to be at a higher temperature than the wood.

D. For the blocks to feel the same, the wood would have to be at a higher temperature than the metal.

E. The blocks would never feel as hot or as cold as each other.

They feel the same when they are the same temperature as you. Then there is no (net) heat energy transfer between you and the blocks.

3) Which statement below is true about heat energy transfer by radiation?

A. Does not require matter (e.g., a solid, liquid or gas).

B. Transfers heat energy into a system better than it transfers heat energy out of a system.

C. Requires long-term displacement (large-scale motion) of individual molecules.

D. Will only transfer heat energy through a solid.

E. None of these statements is true.

That's how the sun warms us up across empty space.

 

4) We normally use the Kelvin scale of temperatures because this scale:

A. Only works for measuring the temperatures of gases.

B. References zero degrees as the temperature where helium gas turns to liquid.

C. Is referenced to the temperature where nothing moves.

D. Is referenced to the temperature where water freezes.

E. Doesn't have any negative numbers in it.

 

(Questions 5-9)

A colleague from the obscure country of Yubania calls to ask how to build and use a "fire syringe." Telephone communications across the Arctic Ocean are poor that day, and your colleague doesn’t understand key elements of your description. He later sends you a videotape of his attempts to make fire with the syringe. For his first attempt you realize, to your horror, that he is actually very quickly pulling up on the plunger such that the volume of the 25 °C nitrogen gas (N2) in the device increases by a factor of ten.

5) Before your colleague attempts the fire syringe demonstration, he correctly explains to his class the origin of pressure for an ideal gas by talking about balls bouncing around in a box. Which of the following would NOT have been mentioned in his explanation (because it does NOT affect pressure)?

A. the mass of the individual ideal gas molecules

B. the average velocity of an ideal gas molecule

C. the average kinetic energy of an ideal gas molecule

D. the number of ideal gas molecules in the syringe

E. A), B), C) & D) all are important for explaining the origin of pressure

Yup, they are all important.

6) During your colleague’s first attempt to work the fire syringe, heat energy:

A. is transferring from the fire syringe to the room.

B. is transferring from the room to the fire syringe.

C. transfer between the fire syringe and the room is negligible.

The key word is "quickly." There isn't time for heat energy to transfer.

7) During the demonstration, the internal energy of the nitrogen gas:

A. increases

B. decreases --just the opposite of the fire syringe as we saw it in class. The air inside cools.

C. is unaffected by the demonstration

 

By this time it is clear from the videotape that your colleague is perplexed. On his second attempt he repeats the experiment, but lifts the plunger very slowly, again increasing the volume of the 25 °C nitrogen gas by a factor of ten. The final temperature of the gas is found to be 25 °C (room temperature).

8) During this process, the internal energy of the nitrogen gas:

A. increases

B. decreases

C. is unaffected by the demonstration--has to be, the temperature doesn't change.

9) During this (second) process, heat energy:

A. is transferring from the fire syringe to the room.

B. is transferring from the room to the fire syringe.-- it had better if the gas is to stay at the same temperature.

C. transfer between the fire syringe and the room is negligible.

10) Two blocks, A and B, of equal mass, that are made of different materials, are each at a temperature of 80oC. Each of the blocks are immersed separately into a bucket, each bucket containing the same amount of water initially at room temperature.

It is observed that the water with block A settles at a temperature of 60oC while the water with block B settles a temperature of 40oC.

What can you say about the properties of the materials of the blocks?

A. The material of A can store more energy than the material of B.

B. The material of B can store more energy than the material of A.

C. Energy is able to flow faster from block A than from block B.

D. Energy is able to flow faster from block B than from block A.

E. We cannot say anything unless we are given more information.

11) The notion of a "black body," where an object emits electromagnetic (EM) radiation according to its temperature, helps us:

A. explain how the warm air from a wood stove travels across the room to keep us warm.

B. estimate the temperature of the sun by examining the "color" of its light.

C. visualize how gas molecules create pressure by bouncing off walls.

D. to understand how signals are transmitted to radios and tv sets.

E. All of the above are correct.

12) Which of the following does NOT correctly describe a heat engine?

A. a heat engine involves the transfer of heat energy.

B. a heat engine converts some of the transferred heat energy to useful work.

C. heat engines operate in cycles such that the net heat energy transfer is always zero.

D. even perfect heat engine operate at less than 100% efficiency.

E. all of the above correctly describe a heat engine.

13) You have a covered Styrofoam cup which contains a mixture of ice and water at 0°C. The cup is perfectly insulated so that no heat can leak in or out. Heat energy is transferred to the mixture by an immersion heater (in the cup) at a steady rate. Which of the following graphs appropriately describes the shape of the temperature-time graph for this process? E) is the correct graph. The water remains at 0oC until all the ice is melted.

14) You have the following plot giving the spectra of two emitters (black bodies) of EM radiation (light, etc.).

 

(14) To determine the temperatures of the two emitters yourself, you would look at the:

A. amounts of infra-red (IR) radiation under the curves.

B. wavelength where the curves have a peak power.

C. areas under the curves.

D. amount of visible EM radiation (light) under the curve.

E. both B) and C) are correct.

15) The principle reason why the Earth has weather systems is:

A. to give weathermen something to talk about.

B. because the sun heats the Earth more at the equator.

C. because the Earth is spinning, which causes Coriolis forces on winds.

D. because nature abhors a vacuum.

E. because the Earth's axis of rotation is tilted relative to the plane containing the Earth, other planet and the sun (the ecliptic plane).

Coriolis forces certainly play a role in the Earth's weather system, but differential heating (more at the equator) drives the entire weather system. The Earth's tilt relative to the plane of the solar system is what causes seasons.