Physical Science - Chapter 7 Notes

Good Absorbers and Good Emitters

are dark in color

Poor Absorbers and Poor Emitter

are reflective or light in color

Green House Effect

named for a similar temperature raising effect in flossiest' greenhouses

Heat of Vaporization

**540 cal/g**

Heat of fusion

**80 cal/g**

Visible Waves

.5X10^-6

Which is the better statement? A. A black object absorbs energy well B. An object that absorbs energy well is black C. Both say the same thing, so both are equivalent D. Both are untrue

B. An object that absorbs energy well is black

If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be A. lower B. higher C. unaffected D. none of the above

B. higher

Although warm air rises why are mountaintops cold and snow covered while the valleys below are relatively warm and green? A. Warm air cools when rising B. There is a thick insulating blanket or air above valleys C. Both of the above D. None of the Above

C. Both of the Above

If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A. Yes B. In some cases, yes C. No D. In some cases, no

C. No

If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A. yes B. in some cases, yes C. no D. in some cases, no

C. No

When a liquid is brought to a boil the boiling process tends to A. resists a further change of phase B. heat the liquid C. cool the liquid D. radiate energy from the system

C. cool the liquid

Evaporation Process

Molecules in liquid move randomly at various speed (collisions). Some molecules gain kinetic energy, others lose kinetic energy. Some energetic molecules escape from the liquid and become gas. Average kinetic energy of the remanding molecules in the liquid decrease, resulting in cooler water.

When thermal insulation, such as spun glass or rock wool, is placed beneath the roof of a house, then in cold weather the insulation will A. create heat to warm the house B. keep the cold from coming through the roof C. slow the flow of heat from inside the house to the outside D. stop the flow of heat from inside the house to the outside

C. slow the flow of heat from inside the house to the outside

Evaporation

Change of phase from liquid to gas

Sublimation

Form of phase change directly from solid to gas

Condensation Process

Opposite of evaporation; warming process from a gas to a liquid; gas molecules near a liquid surface are attracted to the liquid; they strike the surface with increase kinetic energy, becoming part of the liquid

Cooling by Expansion

Opposite to the warming that occurs when air is compressed

Evaporation Application

Pigs have no sweat glands and therefore cannot cool by the evaporation or perspiration. Instead, they wallow...

Heat Transfer

Processes of thermal energy transfer: Conduction Convection Radiation

Boiling

Rapid evaporation occurs beneath the surface of a liquid

Energy is ______ when change of phase is from gas to solid.

Released

Insulation Example

Rock wool or fiberglass between walls slows the transfer of internal energy from a warm house to a cool exterior in winter...

Conduction Application

Snow patterns on the roof of a house show areas of conduction and insulation. Bare parts show where heat from inside has conducted through the roof and melted the snow.

Cooling by Expansion (Example)

The "cloudy" region above hot steam issuing from the nozzle of a pressure cooker is cool to the touch (a combination of air expansion and mixing with cooler surrounding air). Careful, the part at the nozzle that you can't see is steam.

Emission and Absorption

The surface of any material both absorbs and emits radiant energy. When a surface absorbs more energy than it emits, it is a net absorber, and temperature tends to rise. When a surface emits more energy than it absorbs, it is a net emitter, and temperature tends to fall.

Pressure Cooker

The tight lid of a pressure cooker holds pressurized vapor above the water surface which inhibits boiling. In this way, the boiling point of water is greater than 100C.

Insulation

doesn't prevent the flow of thermal energy it slows the rate at which internal energy flows

Freezing

going from a liquid to a solid

Melting

going from a solid to a liquid

Heat of Vaporization (Lv)

is the amount of energy needed to change one gram of substance from a liquid to a gas

Heat of Fusion (Lf)

is the amount of energy needed to change one gram of substance from a solid to a liquid

Boiling occurs when:

the Vapor Pressure of the liquid is equal to the atmospheric pressure --Vapor Pressure depends on temperature

Absorption of Radiation

the ability of a material to absorb and radiate thermal energy is indicated by its color

Radiation

transfer of energy via electromagnetic waves that can travel through empty space

Convection

transfer of heat involving only bulk motion of fluids

Conduction

transfer of internal energy by electron and molecular collisions within a substance

(boiling) Heating warms the

water from below

Wave Frequency - Temperature

(a) A low temperature (cool) source emits primarily low frequency, long wavelength waves (b) A medium temperature source emits primarily medium frequency (c) A high temperature source emits primarily high frequency, short wavelength waves

Equilibrium

(a) in a mixture of ice and water at 0C, ice crystals gains and lose water molecules at the same time. The ice and water are in thermal equilibrium. (b) This gaining and losing process is inhibited hen salt is added to the water. Then with fewer water molecules at the interface, fewer enter the ice.

Understanding the greenhouse effect requires two concepts:

--All things radiate at a frequency (and therefore wavelength) that depends on the temperature of the emitting object --Transparency of things depends on the wavelength of radiation

Heat Transfer: Conduction

--Conduction occurs predominately in solids where the molecules remain in relatively restricted locations.

Climate Change and the Greenhouse Effect

--Energy absorbed from the sun --Part reradiated by Earth as longer-wavelength terrestrial radiation

Emission of Radiant Energy

--Every object above absolute zero radiates --From the Sun's surface comes light, or solar radiation --From the Earth's surface is terrestrial radiation in the form of infrared waves below our threshold of sight

Newton's Law of Cooling Example

--Hot apple pie cools more quickly in a freezer than if left on the kitchen table --Warmer house more quickly leaks thermal energy to the outside than a cooler house --Frozen food warm quicker in a warm room than in a cold room

Phases of Matter

--Matter exists in the three common phases: solid, liquid, and gas (a fourth phase of matter is plasma) --When matter changes from on phase to another, energy is transferred

Climate Change (continues)

--Terrestrial radiation absorbed by atmospheric gases and re-emitted as long-wavelength terrestrial radiation back to Earth --Reradiated energy unable to escape, so warming of Earth occurs --Long-term effects on climate are of present concern

Convection Examples:

--Visible shimmer of air above a hot stove or above asphalt on a hot day --Visible shimmers in water due to temperature difference

Newton's Law of Cooling

--approximately proportional to the temperature difference ΔT between the object and its surroundings --In short: Rate of cooling ~ ΔT

Good Conductors

--composed of atoms with "loose" outer electrons --known as poor insulators --examples: all metals to varying degrees

Reflection of Radiant Energy

--darkness is often due to reflection of light back and forth many times partially absorbing with each reflection --good reflectors are poor absorbers

Poor Conductors

--delay the transfer of heat --known as good insulators -- examples: wood, wool, straw, paper, Styrofoam, cork, liquid, gases, air, or materials with trapped air

Examples of sublimation

--dry ice --mothballs --frozen water

Emission of Radiant Energy

.... (know how to interpret graph)

Gamma Ray

10^-12

Convection Currents

Convection currents produced by unequal heating of land and water. During the day, warm air above the land rises, and cooler air over the water moves in to replace it. At night, the direction of air flow is reversed.

Which of the following does NOT emit radiation? A. a lit fluorescent lamp B. a lit incandescent lamp C. a burned out incandescent lamp D. none of the above

D. none of the above

Condensation Application

If you're chilly outside the shower stall, step back inside and be warmed by the condensation of the excess water vapor in the shower. Evaporation cools you. Condensation warms you!

Boiling Process

Evaporation beneath the surface forms vapor bubbles. Bubbles rise to the surface. If vapor pressure in the bubble is less than the surrounding pressure, then the bubbles collapse. Hence, bubbles don't form at temperature below...

(boiling) Boiling cool the

water from above

Radio Waves

10^3

When a liquid changes phase to a gas, it A. absorbs energy B. emits energy C. neither absorbs nor emits energy D. becomes more conduction

A. absorbs energy

Thermal conduction has much to do with A. electrons B. protons C. neutrons D. ions

A. electrons

It is commonly thought that a can of beverage will cool faster in the coldest part of the refrigerator. Knowledge of Newton's law of cooling A. supports this knowledge B. shows this knowledge is false C. may or may not support this knowledge D. may or may not contradict this knowledge

A. supports this knowledge

Energy is _______ when change of phase is from solid to gas.

Absorbed

ROYGBV (rainbow colors)

High Frequency -----> Lower Frequency

Reason Warm Air Rises

Warm air expands, becomes less dense and is buoyed upward. Air rises until its density equals that of the surrounding air Example: Smoke from a campfire rises and blends with he surrounding cool air

Heat Transfer: Radiation

Wavelength of radiation is related to the frequency of vibration. low frequency vibration--> long waves high frequency vibration--> short waves

Emission and Absorption

Whether a surface is a net absorber or net emitter depends on whether its temperature is above or below that of its surroundings. A surface hotter than its surroundings will be a net emitter and tends to cool. A surface colder than its surroundings will be a net absorber and tend to warm.

Newton's Law of Cooling

applies to rate of warming Object cooler than its surroundings warms up at a rate proportional to ΔT