# Physics chapter 7

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Metals are both good heat and electrical conductors due to
looseness of outer electrons in metal atoms.
A good heat conductor
poor insulator.
A poor conductor of heat is
a good insulator
Your toes feel warmer on a rug than on a tile floor because the rug
is a better insulator than tile
If you were caught in freezing weather with only a candle for warmth, you would be warmer in
an igloo
One of the main reasons people can walk barefoot on red-hot coals of wood without burning their feet has to do with
low thermal conductivity of the coals
A water-filled paper cup held in a flame will not catch fire because
the paper cup cannot become appreciably hotter than the water it contains
The process of convection occurs in
fluids
Warm air rises because faster moving molecules tend to move to regions of less
pressure and density
Hot steam that issues from a pressure cooker expands and
cools
Convection currents in the air near a seashore are produced by
unequal heating of land and water
Coastal winds shift from night to day due to
convection
cooler
If a volume of air is warmed, it expands. If a volume of air expands, it
cools
When a volume of air is compressed, its temperature
increases
The gush of steam that issues from the escape valve of a pressure cooker is relatively cool
above the opening where expansion is prominent
Radiant energy emitted by our planet is
-the result of radioactivity in Earth’s interior.
-terrestrial energy.
-electromagnetic.
The higher the frequency of a wave, the
shorter the wavelength
The average frequency of radiant energy is directly proportional to the
kelvin temperature of the emitter.
The higher the temperature of an object, the
The higher the temperature of an object, the
A star that is twice as hot as another has twice the
Fahrenheit temperature
If an object radiates more energy than it absorbs, its
-thermal energy and temp decreases
-temperature decreases
If an object radiates more energy than it reflects, its
-temperature decreases.
-thermal energy decreases
Objects that are good radiators generally
Hot water will cool to room temperature faster in a
black pot
Cold water will warm to room temperature faster in a
black pot
To minimize heat loss it is best that a teapot be
silver
The pupil of your eye is a net
An object will normally be a net radiator of energy when its temperature is
higher than its surroundings.
If air were a better conductor than it is, nighttimes on Earth would be
considerably colder
If a poor absorber of radiation were a good emitter, its temperature would be
less than its surroundings
A good absorber of radiation is a
A good reflector of radiation is a
The Sun’s radiant energy is composed of shorter wavelengths than the Earth’s because the Sun
has a higher temperature than the Earth.
The silver coating on the glass surfaces of a Thermos bottle reduces energy that is transferred by
Suppose you are served coffee at a restaurant before you are ready to drink it. In order for it to be the hottest when you are ready for it, you should add cream
right away
Suppose you want to save energy and you’re going to leave your warm house for a half hour on a cold day. You should turn the thermostat
off
Suppose you want to save energy and you’re going to leave your cool house for a half hour on a hot day. You should turn the temperature setting on the air conditioner
off
Newton’s law of cooling applies to objects that are
-warming
-cooling
A friend says that a can of beverage will cool faster in the coldest part of a refrigerator. Knowledge of Newton’s law of cooling
supports this statement
A can of soft drink will cool faster if placed in what part of a refrigerator?
the freezer
A red-hot piece of iron will cool faster in a
cold room
Compared to a glass of ice water with ice, a glass of plain ice-cold water without ice on a warm day will warm up
faster
If the greenhouse effect on Earth were absent, Earth’s average temperature would be about
-18°C.
To say you can never change only one thing means that when you change something,
something else changes
Glass in a florist’s greenhouse blocks radiation of
all frequencies
Glass and the atmosphere are largely opaque to
infrared light
Transparency of the atmosphere is lowest for radiation of
infrared light
The interior of a greenhouse emits long-wavelength radiation due to its
temperature
Heating the Earth’s atmosphere is caused by energy
-consumption
-production
The Earth loses heat mainly by
Which is not a phase of matter
vacuum
The molecules in a room-temperature glass of water jostle around at
great variety of speeds
Evaporation is a cooling process because
the more energetic molecules are able to escape the liquid.
To say that evaporation is a cooling process is to say that the
water left behind cools.
Put a saucer of water on your table. A process that occurs in the saucer is
-condensation
-evaporation
The dew that forms on a cold soda can when taken from a refrigerator is due to
condensation
Sublimation is a change of phase from solid to gas without
passing through the liquid phase
A mixture of light and heavy molecules make up a sample of gas. The temperature of the gas is constant, which means all the molecules have the same average
kinetic energy
At the same temperature, which move with the greater speed in a gas?
light molecules
Both heavy and light molecules make up a sample of gas. On average, the faster molecules are the
light ones
In a gaseous mixture of hydrogen and oxygen, the higher-temperature molecules are
both the same
In a gaseous mixture of hydrogen and oxygen, the molecules having the greatest average kinetic energy are
both the same
In a gaseous mixture of hydrogen and oxygen, the faster molecules on average are
hydrogen
In a gaseous mixture of hydrogen and oxygen, the slower molecules on average are
oxygen
If molecules in a sample of gas moved so they completely missed each other, the gas’s temperature would
remain unchanged
A hot dog pants
to help evaporation occur in its mouth and bronchial tract
Pigs wallow in mud mainly to
cool themselves by evaporation
A soda pop can with a small amount of water is on a hot stove. Soon steam comes from its opening. When the can is quickly inverted into a pan of water, the can is crushed by
atmospheric pressure
Consider a steaming aluminum soda-pop can that contains a small amount of boiling water. When it is quickly inverted into a bath of cooler water, the can is dramatically crushed. This is due to the rapidly reduced pressure inside the can by
condensation of steam inside
The process of boiling water tends to
cool the water
Boiling can be thought of as evaporation
beneath the surface of water
Boiling and freezing can occur at the same time when water is subjected to
decreased atmospheric pressure
When heat is added to boiling water, the water temperature
remains the same
Increased air pressure on the surface of hot water tends to
prevent boiling
In the mountains, water boils at
a lower temperature than at sea level
When salt is introduced to water, the temperature at which freezing occurs is
lowered
Food is cooked faster in a pressure cooker because of the
higher temperature
If you want to cook eggs by boiling them while in the mountains, then compared with cooking at sea level you should
boil the eggs for a longer time
When bringing water to a boil in the mountains, the time needed to reach the boiling point is
less than at sea level
Melting and freezing are both
-opposite processes
-changes of phase
-processes of molecular transfer
Keep decreasing the shaking of atoms in a liquid and it will
solidify
When water changes to ice, water molecules
release energy
When ice changes phase to become water, energy is
absorbed
An researcher discovers a harmless and tasteless salt, which, when added to water changes its boiling point. The market value for this salt will be best if the salt
raises the boiling point of water
Which requires more energy?
changing 1 gram of 100°C water to 100°C steam
Which would burn the most?
100 g of steam at 100°C
Steam burns are much more damaging than boiling-water burns because steam
contains more thermal energy
Steam burns are more damaging than burns caused by boiling water because steam
-has more energy per kilogram than boiling water
-releases additional energy when it condenses
When steam condenses to water, energy is
released
When a gas is changed to a liquid phase, the gas
releases energy
When a solid is changed to a liquid phase, the solid
absorbs energy
When gases change to a liquid phase, they
release energy
We feel uncomfortably warm on a muggy day because water molecules are
condensing on our bodies
We are warmed by condensation because water molecules in the air striking our bodies
transfer some of their kinetic energies to us
When snow forms in clouds, the surrounding air is
warmed
When a gas changes phase to become a solid, energy is
released
Suppose you walk on red hot coals with bare feet. Providing bits of coal do not stick to your feet, it would be safer if your feet are
wet
To melt 50 g of 0°C ice requires
-80 calories
-25 calories
-50 calories
-none of the above*
The number of grams of ice that can be melted by 1 g of 100°C steam is
6.75 g
If the composition of the upper atmosphere were changed to permit a greater amount of terrestrial radiation to escape, what effect would this have on Earth’s climate?
If more terrestrial radiation in the upper atmosphere escaped, Earth’s climate would be cooler
Alcohol evaporates faster than water at the same temperature. Which cools your skin more: alcohol, or the same amount of water, evaporating from your skin?
alcohol
From best to worst, rank these materials as heat conductors: (a) copper wire, (b) snow, and a (c) glass rod.
1. copper wire (best)
2. glass rod
3. snow (worst)
From greatest to least, rank the energy needed for these phase changes for equal amounts of H2O: (a) from ice to ice water, (b) from ice-water to boiling water, and (c) from boiling water to steam.
1. boiling water to steam (most energy)
2. ice water to boiling water
3. ice to ice water

A block of ice at 0∘C is dropped from a height that causes it to completely melt upon impact. Assume that there is no air resistance and that all the energy goes into melting the ice.

What is the height necessary for this to occur. [ Hint: Equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (Lf = 335,000 J/kg).].

h=34 km

no

A 11-kg iron ball is dropped onto a pavement from a height of 100 m . Suppose that half of the heat generated goes into warming the ball.

What is the temperature increase of the ball. (The specific heat capacity of iron is 450 J/kg ⋅ ∘C. Use 9.8 N/kg for g.).

is answer same for iron ball of any mass?

ΔT = 1.1 ∘C

yes

Quantity of heat: Q=cmΔT

Find what heat in calories (cal) is required to increase the temperature of 60 g water from 0∘C to 60 ∘C. The specific heat capacity of water is 1 cal/g⋅∘C.

3600 cal

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