Chapter 7 Physics HW

A quality perfume is a mixture of essential oils and has a scent that changes with time and skin temperature. Explain the gradual change of the perfume's scent with time in terms of evaporation. Option A: Different oils in the perfume evaporate at different rates. Option B: As more of the perfume evaporates, the scent changes. Option C: The perfume's scent changes as time passes. Option D: When the perfume is all evaporated, the scent will be gone.

Option A: Different oils in the perfume evaporate at different rates.

If you were laying steel track for a railroad, what influence would thermal expansion have on your work? Option A: I would need to account for the steel rail changing its size as the temperature rises and falls. Option B: It would not be a problem, as any changes in the size of the steel rail would be negligible. Option C: None, since thermal expansion does not occur with steel. Option D: It would not be a problem, since any temperature-related change in size of the rails would also apply to the wheels of the trains.

Option A: I would need to account for the steel rail changing its size as the temperature rises and falls.

If you add a little hot tea to ice water at 0 °C, the mixture will end up at 0 °C as long as some ice remains. Where does the tea's extra thermal energy go? Option A: It melts some of the ice. Option B: It is absorbed. Option C: It cools off. Option D: It warms up.

Option A: It melts some of the ice.

If you put a warm bottle of wine in a container of ice water, the wine will cool but the ice water won't become warmer. Where is the wine's thermal energy going? Option A: It melts some of the ice. Option B: It is absorbed. Option C: It cools off. Option D: It heats up.

Option A: It melts some of the ice.

An icy sidewalk gradually loses its ice even when the weather stays cold. Where does the ice go? Option A: It sublimes into the air. Option B: The sun melts it. Option C: Putting salt on the sidewalk will cause the ice to melt. Option D: It evaporates into the air.

Option A: It sublimes into the air.

Some air fresheners are solid materials that have strong odors. If you leave these air fresheners out, they slowly disappear. What happens to the solid material? Option A: It sublimes into the surrounding air. Option B: It evaporates into the surrounding air. Option C: It melts. Option D: It dissolves.

Option A: It sublimes into the surrounding air.

Your body is presently converting chemical potential energy from food into thermal energy at a rate of about 100 J/s, or 100 W. If heat were flowing out of you at a rate of about 200 W, what would happen to your body temperature? Option A: It would decrease. Option B: It would increase. Option C: It would remain constant. Option D: More information is needed to be able to answer.

Option A: It would decrease.

Use the concept of convection to explain why firewood burns better when it's raised above the bottom of a fireplace on a grate. Option A: Raising the wood allows convection to cause air to circulate around the wood, giving it more oxygen. Option B: Convection pulls in cooler air to the bottom. Option C: Convection causes warmer air to rise. Option D: Raising the wood allows convection to carry away the heat better.

Option A: Raising the wood allows convection to cause air to circulate around the wood, giving it more oxygen.

Putting a clear plastic sheet over a swimming pool helps keep the water warm during dry weather. Explain. Option A: Sunlight can penetrate through to the water, and no heat is being carried away by evaporating water. Option B: Sunlight can penetrate through to the water, and the plastic sheet traps the heat. Option C: Sunlight can penetrate through to the water, and the plastic sheet makes the pressure go up. Option D: Sunlight can penetrate through to the water.

Option A: Sunlight can penetrate through to the water, and no heat is being carried away by evaporating water.

Why do bridges have special gaps at their ends to allow them to change lengths? Option A: Temperature changes will cause the bridge to expand and contract. Option B: The gaps give the bridge room to expand on a cold day. Option C: As the metal of the bridge fatigues with age and traffic, the bridge will change its length. Option D: The gaps are a safety margin in case the metal of the bridge is cut to the wrong length.

Option A: Temperature changes will cause the bridge to expand and contract.

The molecules of antifreeze dissolve easily in water. Why does adding antifreeze to the water in a car radiator keep the water from freezing in the winter and boiling in the summer? Option A: The antifreeze lowers the freezing temperature and raises the boiling temperature of the water. Option B: It increases the pressure in the radiator, which keeps the water from freezing or boiling. Option C: The presence of the antifreeze chemically changes the water into a different compound, which cannot freeze. Option D: The antifreeze bonds with the radiator to keep the water from freezing.

Option A: The antifreeze lowers the freezing temperature and raises the boiling temperature of the water.

You're floating outside the space station when your fellow astronaut tosses you a cold bottle of mineral water. It's outside your space suit but you open it anyway. It immediately begins to boil. Why? Option A: The boiling point of water is much lower at very low pressure. Option B: Liquids always boil at zero pressure. Option C: There is nothing to keep the water in liquid form. Option D: Nature abhors a vaccum, so the water boils.

Option A: The boiling point of water is much lower at very low pressure.

You have a roll of papered foil that is shiny on one side and black on the other. You wrap a cold potato salad in that foil. Which side should be facing outward to keep the salad cold longest? Option A: The foil side. Option B: The black side. Option C: It doesn't matter which side.

Option A: The foil side.

A difficult-to-open jar may open easily after being run under hot water for a moment. Explain. Option A: The heat from the water makes the lid expand and loosen. Option B: The water lubricates the lid. Option C: The heat from the water causes the air inside the jar to expand, exerting pressure on the lid. Option D: This doesn't really work; the effect is really an old wives' tale.

Option A: The heat from the water makes the lid expand and loosen.

If you remove ice cubes from the freezer with wet hands, the cubes often freeze to your fingers. How can the ice freeze the water on your hands? Shouldn't they melt instead? Option A: The ice cubes are well below 0 °C, so they can pull heat from the water on your hands before they start to melt. Option B: The water from your hands freezes onto the ice cubes. Option C: The ice cubes melt a little, then all the water freezes. Option D: The ice is colder than the water.

Option A: The ice cubes are well below 0 °C, so they can pull heat from the water on your hands before they start to melt.

A doctor can study a patient's circulation by imaging the infrared light emitted by the patient's skin. Tissue with poor blood flow is relatively cool. What changes in the infrared emissions would indicate such a cool spot? Option A: The infrared emissions from the cool spot would be less bright and shifted toward longer wavelengths. Option B: The infrared emissions from the cool spot would be less bright and shifted toward shorter wavelengths. Option C: The infrared emissions from the cool spot would be less bright. Option D: The infrared emissions from the cool spot would be shifted toward longer wavelengths.

Option A: The infrared emissions from the cool spot would be less bright and shifted toward longer wavelengths.

You can use a blender to crush ice cubes, but if you leave it churning too long, the ice will melt. What supplies the energy needed to melt the ice? Option A: The kinetic energy of the blender blades. Option B: The heat from the surroundings. Option C: The light from the surroundings. Option D: Nothing. The ice just naturally melts.

Option A: The kinetic energy of the blender blades.

Doctors use an infrared camera to look for inflammation, which appears as a hot patch on otherwise cooler skin. What differences would the camera observe at this hot patch? Option A: The light from the hot patch would be brighter and have a shorter wavelength than light from the surrounding skin. Option B: The hot patch would appear brighter than light from the surrounding skin. Option C: The light from the hot patch would have a shorter wavelength than light from the surrounding skin. Option D: The light from the hot patch would be brighter and have a longer wavelength than light from the surrounding skin.

Option A: The light from the hot patch would be brighter and have a shorter wavelength than light from the surrounding skin.

You are hired as an engineer at a thermometer factory. Suppose you built a water thermometer by replacing the mercury in a mercury thermometer with water. You want to measure temperatures above freezing with it. How would it behave as the temperature drops from 5o C to 1o C? Option A: The reading will decrease and then begin increasing. Option B: The reading will steadily decrease. Option C: The reading will steadily increase. Option D: The reading will increase and then begin decreasing.

Option A: The reading will decrease and then begin increasing.

When you put a loaf of bread in a plastic bag, there is still air around the bread. Why doesn't the bread dry out as quickly in the bag as it does when there's no bag around it? Option A: The relative humidity of the air in the bag reaches 100%. Option B: The bag seals in the moisture. Option C: The water evaporates into the air. Option D: The water sublimes into the air.

Option A: The relative humidity of the air in the bag reaches 100%.

Explain how convection contributes to the shape of a candle flame. Option A: The rising warm air causes the flame to elongate upward. Option B: The warm air rises. Option C: Cooler air comes in at the bottom. Option D: The flame radiates heat upward.

Option A: The rising warm air causes the flame to elongate upward.

On a bitter cold day, the snow is light and powdery. This snow doesn't begin melting immediately when you bring it into a warm room. Why? Option A: The snow's temperature needs to rise to 0 °C before it can start melting. Option B: The snow needs to come up to room temperature before it can start melting. Option C: The snow needs some time before it can start melting. Option D: The warmth of the room takes a while to penetrate the snow.

Option A: The snow's temperature needs to rise to 0 °C before it can start melting.

Why are concrete sidewalks divided into individual squares rather than being left as continuous concrete strips? Option A: The space between the squares gives the concrete room to expand on a hot day. Option B: It is easier to pour concrete in squares than as a continuous strip. Option C: The space between the squares gives the concrete room to expand on a cold day. Option D: If a square is damaged it is cheaper to replace than if an continuous strip were damaged.

Option A: The space between the squares gives the concrete room to expand on a hot day.

Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun sets near the seashore. Option A: The surface wind will blow from the land toward the water. Option B: The surface wind will blow alternately back and forth along the shore, parallel to the boundary between land and water. It will reverse directions every few minutes. Option C: The surface wind will blow steadily in one direction along the shore, parallel to the boundary between land and water. Option D: The surface wind will blow from the water toward the land.

Option A: The surface wind will blow from the land toward the water.

Astronomers can tell the surface temperature of a distant star without visiting it. How is this done? Option A: They use the color temperature of the star's light. Option B: They determine how much heat the star gives off. Option C: They use the red shift of the light. Option D: They determine the distance to the star.

Option A: They use the color temperature of the star's light.

A shiny, white transparent surface prevents heat transfer because Option A: it has emissivity of zero and reflects all light that strikes it. Option B: it has emissivity of 1 and reflects all light that strikes it. Option C: it has emissivity of zero and absorbs all light that strikes it. Option D: it has emissivity of 1 and absorbs all light that strikes it.

Option A: it has emissivity of zero and reflects all light that strikes it.

A pedestrian bridge crosses a street. This bridge is entirely supported by columns from below. A gap at each end of the bridge separates the bridge's surface from the sidewalks leading to the bridge. The width of each gap changes with time. This width is smallest Option A: on hot days. Option B: at noon. Option C: at midnight. Option D: on cold day.

Option A: on hot days.

Wind is one of nature's ways of transferring energy through Option A: conduction. Option B: convection. Option C: transmission. Option D: radiation.

Option B: convection

People fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. If there is trouble, a fire fighter can lie under the tent to block the heat from burning trees overhead. The tent helps because Option A: conduction carries heat downward toward the fire fighter and the aluminum tent conducts that heat harmlessly into the ground. Option B: radiation carries heat downward toward the fire fighter and the aluminum tent reflects most of that radiation. Option C: convection carries heat downward toward the fire fighter and the aluminum tent blocks most of the heat carried by convection. Option D: both conduction and radiation carry heat downward toward the fire fighter and the aluminum tent blocks most of that heat.

Option B: radiation carries heat downward toward the fire fighter and the aluminum tent reflects most of that radiation.

Housing and natural animal insulation works because Option A: the insulating materials are poorer heat conductors than air. Option B: the insulating materials trap air and prevent convection. Option C: the insulating materials prevent radiation. Option D: the insulating materials reflect radiation.

Option B: the insulating materials trap air and prevent convection.

Why are good thermal conductors generally good electric conductors also? Option A: Heat and electricity are the same things. Option B: The molecules in both don't move around very much. Option C: Electron motion is responsible for determining both properties. Option D: The answer depends on the specific metal.

Option C: Electron motion is responsible for determining both properties.

Why does the handle of a metal spoon submerged in boiling soup feel hot ? Option A: from the soup is transferred through the spoon by convection. Option B: The spoon has given up all its cold to the soup. Option C: Heat from the soup is transferred through the spoon by conduction. Option D: Heat from the soup is transferred through the spoon by radiation.

Option C: Heat from the soup is transferred through the spoon by conduction.

Why does an ice cube feel cold? Option A: Heat from your hand enters the cube by convection. Option B: Cold from the cube enters your hand by convection. Option C: Heat from your hand enters the cube by conduction. Option D: Cold from the cube enters your hand by conduction.

Option C: Heat from your hand enters the cube by conduction.

Ice is ___________. Option A: amorphous Option B: very disordered Option C: crystalline Option D: just like liquid water only it move slower

Option C: crystalline

Freezing is a ____________ that requires energy ________ for the melting system. Option A: phase transition; input Option B: chemical change; input Option C: phase transition; release Option D: chemical change; release

Option C: phase transition; release

When cooking a potato in a conventional oven it is useful to stick a nail in it, which makes it cook faster. This is because Option A: the nail is a good radiator of heat. Option B: the nail promotes convection in the potato. Option C: the nail is a good conductor of heat. Option D: the nail gets much hotter than anything in the oven.

Option C: the nail is a good conductor of heat.

A popular classroom demonstration involves placing a paper cup with water in it on a burner, and boiling the water in the cup. Although part of the cup may burn, the part containing the water does not because Option A: paper is a poor conductor of heat. Option B: it all happens too quickly for the paper to burn. Option C: the water absorbs most of the heat from the flame. Option D: the evolving steam burns the paper on the cup above the water line.

Option C: the water absorbs most of the heat from the flame.

You are watching a science fiction movie where people on a space ship are traveling around the universe observing stars with different temperatures. Which of the following stars has the lowest surface temperature? Option A: A bluish star Option B: A yellowish star Option C: The sun Option D: A reddish star

Option D: A reddish star

Which temperature scale has 373 as the boiling point of water? Option A: Fahrenheit Option B: Celsius Option C: Centigrade Option D: Kelvin

Option D: Kelvin

Soil heats up much faster than water when the two are exposed to sunlight. Use that fact and your understanding of heat transfer to predict which way the wind will blow near the surface of the earth as the sun rises near the seashore. Option A: The surface wind will blow from the land toward the water. Option B: The surface wind will blow alternately back and forth along the shore, parallel to the boundary between land and water. It will reverse directions every few minutes. Option C: The surface wind will blow steadily in one direction along the shore, parallel to the boundary between land and water. Option D: The surface wind will blow from the water toward the land.

Option D: The surface wind will blow from the water toward the land.

You are a mechanic in a garage and are working on a carburetor that is made of metal, has a glass inspection window and plastic gears for the choke. If all three types of material are at the same temperature and each type of material is in contact with the other two, then Option A: heat will flow from the plastic to the glass, and from the glass to the metal. Option B: heat will flow from the metal to the glass, and from the glass to the plastic. Option C: heat will flow from the glass to both the plastic and the metal. Option D: no heat will flow between any parts.

Option D: no heat will flow between any parts.

Some scientists assert that there would be no life on earth if ice did not have a molecular structure with a lot of open space because Option A: ice would be so light that it could never form, leaving too much water on the Earth's surface. Option B: ice would be less dense than it is now and float too much. Option C: ice would be denser than water and having a solid sink in its own liquid form would violate the conservation of energy. Option D: the density of ice would be greater than water and lakes would freeze solid - from the bottom up.

Option D: the density of ice would be greater than water and lakes would freeze solid - from the bottom up.

A common glass thermometer contains a red or silver liquid that rises upward in a glass tube as the temperature of the thermometer increases. The liquid moves up the tube because Option A: only the glass contracts as its temperature decreases, so the liquid moves up the tube to occupy more of the tube's internal space. Option B: while both the glass and the liquid contract as their temperatures increase, the glass contracts more rapidly than the liquid does. Option C: the pressure of gas above the liquid decreases as its temperature rises and the liquid is sucked upward in the glass tube. Option D: while both the glass and the liquid expand as their temperatures increase, the liquid expands more rapidly than the glass does.

Option D: while both the glass and the liquid expand as their temperatures increase, the liquid expands more rapidly than the glass does.