Physics Test Chapter 15-18

Alcohol evaporates more quickly than water at the same temperature. Which produces more cooling -- alcohol or the same amount of water on your skin?

Alcohol produces more cooling because of its higher rate of evaporation.

Which is the largest unit of heat transfer - Calorie, calorie, or joule?

Calorie

Why does cold mountain air become warm when it descends into a valley?

It warms because it is adiabatically compressed

Soaring birds and glider pilots can remain aloft for hours without expending power. How do they do it?

They ride in "thermals," updrafts of air.

In times past, on a cold winter night, it was common to bring a hot object to bed with you. Which would keep you warmer through the cold night -- a 10-kg iron brick or a 10-kg jug of hot water at the same temperature? Explain.

10 KG of water has a higher specific heat and takes longer to cool.

Consider a jar of helium with a temperature of 0 degrees Celcius. What will be its temperature if it is twice as hot (has twice the internal energy)?

273 degrees Celcius?

Does a common electeric fan cool the air in a room? If not, then why is it used in an overly warm room?

A fan does not cool the room but increases the evaporation of perspiration which cools the body.

After you have driven a car for some distance, why does the air pressure in the tires increase?

As the wheels revolve, they heat up. As the air molecules move faster they expand and the pressure goes up.

Wood is a better insulator than glass, yet fiberglass is commonly used as an insulator in wooden buildings. Explain.

Because air is an excellent insulator and fiberglass has large amounts of trapped air spaces.

Consider two glasses, one filled with water and the other half-full, with the water in the two glasses being at the same temperature. In which glass are the water molecules moving faster? In which is there greater internal energy? In which will more heat be required to increase the temperature by 1 degree Celcius?

Full; it will take more heat for the full cup to raise the temperature, therefore it has a greater internal energy.

what happens to the gas pressure within a sealed gallon can when it is heated? When it is cooled? Why?

Gas pressure increases in the can when heated, and decreases when cooled.

Since energy is radiated by all objects, why can't we see them in the dark?

Human eyes are not sensitive to anything in the infrared spectrum.

An inventor claims to have developed a new perfume that lasts a long time because it doesn't evaporate. Comment on this claim.

If the perfume doesn't evaporate it will produce no odor. The odor of a substance is evidence for its evaporation.

Thermometers in a physics lab often use gas rather than mercury. Whereas changes in volume indicate temperature in a mercury thermometer, what changes in a gass do you think indicate temperature in a gase thermometer?

If the temperature increases, the gas pressure increases.

In terms of thermal expansion, why is it important that a key and its lock be made of the same or similar materials?

If they are different materials, they will expand differently and the lock won't work.

How can water be brought to a boil without heating it?

If we reduce the pressure, it will boil.

Some ceiling fans are reversible so that they drive air down or pull it up. In which direction should the fan drive the air during the winter? In which direction for summer?

In the winter, you want warm air near the floor, so the fan should push warmer ceiling air downward. In the summer, you want cooler air near the floor, so the fan should pull air upward.

If the composition of the upper atmosphere were changed so that it permitted a greater amount of terrestrial radition to escape, what effect would this have on Earth's climate?

More energy would escape and the Earth's climate would be cooler.

Under what conditions would a heat engine be 100% efficient?

Never

Wrap a fur coat around a thermometer. Will the temperature rise?

No, because there is no heat being given off.

Could you cool a kitchen by leaving the refrigerator door open and closing the kitchen door and windows? Explain.

No, the room will warm up because the refrigerator motor will heat the air.

What is the ultimate source of energy in coal, oil, and wood Why do we call energy from wood renewable but energy from coal and oil nonrenwable.

Solar energy is the ultimate source of energy on Earth. It can take 10-20 years to regenerate wood, but it takes millions of years to regenerate coal and oil. That's why we refer to coal and oil as nonrenewable.

Iceland, so named to discourage conquest by expanding empires, is not at all ice covered like Greenland and parts of Siberia, even though it is not far from the Arctic Circle. The average winter temeprature of Iceland is considerably higher than it is in regions at the same latitude in eastern Greenland and central Siberia. Why is this so?

The climate of Iceland is moderated by the surrounding water.

Hydrothermal vents are openings in the ocean floor that discharge very hot water. Water emerging at nearly 280 degrees Celcius from one such vent off the Oregon coast, some 2400 m beneath the surface, is not boiling. Provide an equation.

The hot water is below the boiling point for the very high pressure there, somewhat like the higher boiling point of water in a pressure cooker.

On a cold day, why does a metal doorknob feel colder than the wooden door?

The metal doorknob conducts heat better than wood.

Why does blowing over hot soup cool the soup?

The moving air increases the net evaporation

Why does the bottom of a tire pump feel hot when you pump air in the tire, but when air is released, the valve stem feels cool?

The pump gets hot because you are compressing the air within. The tire valve feels cool because the escaping air is expanding. These are adiabatic processes.

If you were caught in a freezing weather with only your own body heat as a source, would you be warmer in an Arctic igloo or in a wooden shack? Defend your answer.

The snow and ice of the igloo is a better insulator than wood, so you would be warmer in an igloo.

In a meeting room, there are chairs, a table, and people. Which of these things has a temperature (a) lower than (b) greater than, or (c) equal to the temperature of the air?

The tables and chairs are equal to the room temperature while humans have a higher temperature than the room.

Which has the great amount of internal energy -- an iceberg or a cup of hot cofee? Defend your answer.

The tremendous mass of the iceberg will have a higher internal energy than the coffee.

Double-pane windows have nitrogen gas or very dry air between the panes. Why is ordinary air a poor idea?

Visibility of the windows is impaired if there is any condensation of water between the panes of glass. Hence, the gas between the panes should contain no water vapor.

At what common temperature will a block of wood and a block of metal both feel neither hot nor cold to the touch?

When they are both the same temperature as your hand.

An electric fan not only doesn't decrease the temperature of air, but it actually increases air temperature. How, then, are you cooled by a fan on a hot day?

You are cooled by the fan, which blows air over you to increase the rate of evaporation from your skin, but you are a small part of the overall system, which warms.

Why can't you establish whether you are running a high temperature by touching your own forehead?

Your hand is on your forehead, so you cannot tell the difference because your whole body is the same temperature as your forehead.