Exam 2

A refrigerator is running with its door open inside a sealed, perfectly insulated room. The temperature of the room will

increase

To keep the strong magnets in a scientific facility next door from sending flux lines through your office, should you line the office walls with aluminum or with iron?

iron

When you throw a hot rock into a cold puddle, what happens to the overall entropy of the system?

it increases

If you drop a glass vase on the floor, it will become fragments. If you drop those fragments on the floor, however, they will not become a glass vase. Why not?

a fragmented vase has higher entropy than an intact vase

You have an electrically neutral toy that you divide into two pieces. You notice that at least one of those pieces has an electric charge. Do the two pieces attract or repel one another, or neither?

attract

Magnetic poles are

called north and south

If two objects repel one another, you know they have like charges on them. How would you determine whether these charges are both positive or negative?

compare the objects with a charged reference object

After you attract two pieces of adhesive tape from a tape dispenser, those pieces will repel one another. Explain their repulsion.

each piece of tape will acquire opposite charges while being extracted from the tape dispenser

How could you use iron to prevent the magnetic flux lines from a strong button magnet form extending outward into the room?

enclose the magnet in an iron box

Heat naturally flows

from a region of higher temperature to a region of lower temperature

The law of conservation of energy says

heat in equals change in internal energy plus work done

Why would replacing the air inside a metal organ pipe with helium gas raise the pipe's pitch?

helium is less dense than air, so it accelerates more rapidly than air

Some of the strings in a piano are made of steel wire wrapped with a spiral of copper wire. The copper wire doesn't contribute to the tension in the string, so what is its purpose?

it increases the mass of the string, thereby lowering the string's pitch

A tuning peg slips on your violin, lessening the tension in one of the strings. What effect does this change have on the string's sound?

it lowers the pitch (vibrational frequency) of the string

A clothing rack hangs from the ceiling of a store and swings back and forth. Why doesn't the period of this motion depend on how many dresses the rack is holding?

it's length and strength of gravity

Suppose that you had an electrically charged stick. If you divided the stick in half, each half would have had the original charge. If you split each of these halves, each piece would have a quarter of the original charge. Can you keep on dividing the charge in this manner forever?

no, because charge is quantized

Is it possible to have two permanent magnets that always attract one another, regardless of their relative orientations?

no, because the magneostatic forces between magnetic dipoles depend on their relative orientations

The paint or powder particles discussed in Exercise 5 are all given the same electric charge. Why does this type of charging ensure that the coating will be highly uniform?

paint particles of the same net charge experience repulsive forces which tends to spread them out uniformly

"The entropy of an insulated system never decreases." Which law of thermodynamics is this?

second

The outdoor portion of a central air conditioning unit has a fan that blows air across the condenser coils. If this fan breaks, why won't the air conditioner cool the house properly?

the air blown by the fan carries heat away from the condenser coils

Drinking fountains that actively chill the water they serve can't work without ventilation. They usually have louvers on their sides so that are can flow through them. Why do they need this airflow?

the air carries heat away from the heat pump which cools the water

If you bring a button magnet near an iron pipe, they will soon begin attracting one another. Why don't they repel?

the button magnet's magnetic field polarizes the iron pipe and the pipe develops an opposite pole near the approaching the the pole of the button and thus attracts the magnet

In industrial settings, neutral metal objects are often coated by spraying them with electrically charged paint or powder particles. How does placing charge on the particles help them to stick to an object's surface?

the charged particles polarize the neutral metal object

An ion generator clears smoke from room air by electrically charging the smoke particles. Why will those charged smoke particles stick to the walls and furniture?

the charged smoke particles polarize the neutral surfaces

A Ping-Pong ball contains an enormous number of electrically charged particles. Why don't two Ping-Pong balls normally exert electrostatic forces on each other?

the electrostatic forces cancel due to zero net charges on each ball

When you throw a rock into calm water, ripples head outward as several concentric circles. As the circumferences of these circles grow larger, their heights become smaller. Why must the wave's height become smaller as it spreads outward.

the energy in a wave increases when the height or length of its crests increase, so to conserve energy as the wave's circumference increases, its height must decrease

A soda siphon carbonates water by injecting carbon dioxide gas into it. The gas comes compressed in a small steel container. As the gas leaves the container and pushes ints way into the water, why does the container become cold?

the gas in the container is doing work but there is no heat input

Some wind chimes consist of sets of metal rods that emit tones when they're struck by wind-driven clappers. These equal diameter rods bend back and forth as harmonic oscillators. Why do the longer rods emit lower pitched tones than these shorter rods?

the longer rods have more mass and are less stiff than the shorter rods

Hammering or heating a permanent magnet can demagnetize it. What happens to the magnetic domains inside it during these processes?

the magnetic domains will lose their uniform orientations and become more randomly oriented

Do more magnetic flux lines begin or end on a button magnet, or are those numbers equal?

the magnetic flux lines begin/end on a button magnet are equal

Why are the tides relatively weak near the north and south poles?

the moon's gravity produces two tidal bulges in the earth's oceans. those tidal bulges peak near the equator, one of the side of the earth nearest the moon and one on the side of the earth farthest from the moon

After you peel a sticker form its paper backing, the two attract one another. Explain their attraction.

the sticker and its paper backing acquired opposite charges while being separated

Why is a violin vibrating up and down in its fundamental vibrational mode an example of a standing wave rather than a traveling wave?

the strings nodes and antinodes do not move

If you pull downward on the middle of a trampoline and let go, the surface will fluctuate up and down several times. Why is this motion an example of a standing wave?

the trampoline's nodes and antinodes do not move

If you bring two magnetic compasses nearby, they will soon begin attracting one another. Why don't they repel?

the two compass needles rotate until they have minimized their total magneostatic potential energy and thus the opposite poles will point toward one another

If the forces between electric charges didn't diminsh with distance, an electrically charged balloon wouldn't cling to an electrically neutral wall. Why not?

the wall's acctractive and repulsive forces would equal in magnetite and the opposite direction which would result in zero force on the balloon

If you hold a magnetic compass in a uniform magnetic field pointing northward, in which direction, if any, is the net magnetic force on the compass?

there is no magnetic force direction

Why are the highest pitched strings on most instruments, including guitars, violins, and pianos, the most likely strings to break?

to vibrate at the highest pitches, these strings must be thin and taught. that combination makes them prone to breaking

If you place a button magnet in a uniform magnetic field, what is the net force on that button magnet?

zero