quiz 11

What are the three primary mechanisms of heat transfer?

Conduction, convection, and radiation.

At the molecular level, how does heat transfer occur during conduction?

Faster, higher-temperature molecules collide with slower, cooler molecules, transferring kinetic energy from the hot region to the cold region.

Why are metals generally excellent thermal conductors?

They contain many free electrons that roam through the lattice and rapidly carry energy from hot to cold regions.

Why are materials such as wood and cloth poor conductors of heat?

They lack free electrons, so energy transfer relies only on slower atom-to-atom collisions.

What name is given to a material that resists the flow of heat?

A thermal insulator.

How does the phase of a substance influence its thermal conductivity?

Gases are poorest conductors, liquids and solids conduct better, and metals (solid) conduct best because their particles are closer together and— in metals— free electrons aid transfer.

Define thermal conductivity.

A material property that quantifies how readily heat is conducted; higher thermal conductivity means more efficient heat transfer.

What is convection?

Heat transfer by the bulk movement of a fluid caused by density differences that arise from temperature gradients.

Why does warm air or fluid rise during natural convection?

Heating causes it to expand, lowering its density relative to the surrounding cooler fluid, so buoyancy forces it upward.

Give an atmospheric example of natural convection.

Sea breezes (day) and land breezes (night) produced by differential heating of land and water.

What is forced convection?

Convection enhanced by an external device—such as a pump or fan—that moves the fluid to improve heat transfer.

How does a car’s cooling system illustrate forced convection?

A pump circulates hot radiator fluid through the engine, while a fan draws cooler air through the radiator, carrying heat away from the fluid.

In heat transfer, what is radiation?

The transfer of energy by electromagnetic waves (e.g., visible light, infrared) without the need for a material medium.

Can radiant heat transfer occur through a vacuum?

Yes; radiation does not require matter, so it can cross empty space (e.g., sunlight reaching Earth).

Roughly at what temperature does a solid begin to glow red-hot?

≈1000 K.

What is a blackbody?

An ideal surface that absorbs (and therefore can emit) all incident electromagnetic radiation, regardless of wavelength.

How does a black, rough surface compare with a shiny silver surface in absorbing sunlight?

Black, rough surfaces absorb about 97 % of incident radiation; shiny silver surfaces absorb only ~10 % and reflect the rest.

Why do dark-colored clothes feel hotter than light-colored clothes in sunshine?

Dark fabric absorbs more solar radiation and re-emits half of it inward toward the body, increasing perceived warmth.

When an object is in thermal equilibrium with its surroundings, how are radiant absorption and emission related?

The rate of energy absorbed equals the rate emitted, so the object’s temperature remains constant.

What is the greenhouse effect?

Partial trapping of Earth’s outgoing infrared radiation by atmospheric gases, causing the planet’s surface temperature to rise.

Which two atmospheric gases most strongly contribute to the natural greenhouse effect?

Water vapor and carbon dioxide.

Without the greenhouse effect, what would Earth’s average surface temperature be?

About 250 K (–23 °C).

Approximately how much warmer does the greenhouse effect make Earth?

Around 40 K.

How have atmospheric CO₂ levels changed in the past century, and why is this significant?

They have risen by more than 20 % (about 4 % per decade) mainly due to burning fossil fuels, potentially leading to several-kelvin global warming and climate impacts.

What two quantities are multiplied/divided to define pressure (P)?

Force and area (P = F / A).

For two identical books, one flat and one standing, which property remains unchanged?

Their weight remains the same.

Why can Sara lie safely on a bed of sharp nails?

Her weight is distributed over hundreds of nails, greatly reducing pressure on any single point.

When you are standing upright, where is your blood pressure highest?

In your feet.

Why is a dam built thicker at the bottom than at the top?

Because water pressure increases with depth.

On what two factors does the pressure at a point in a liquid depend?

Liquid depth and liquid density.

From which hole in a water tower wall does water spurt out fastest?

The hole closest to the bottom, where pressure is greatest.

A completely submerged object always displaces what amount of fluid?

A volume of fluid equal to its own volume.

If a 10-ton ship floats, what is the buoyant force acting on it?

10 tons (equal to the ship’s weight).

For two submerged 1-cm³ blocks (aluminum and lead), which experiences the greater buoyant force?

Both experience the same buoyant force because they displace the same volume of water.

How does a fish’s density compare with the density of water?

Approximately the same (allowing neutral buoyancy).

Because lobsters live on the ocean floor, how does their density compare with seawater?

It is greater than the density of seawater.

A lobster on a scale at the ocean floor weighs compared with the same lobster weighed in air.

Less, due to the buoyant force of seawater.

How does a life jacket keep you afloat?

It lowers the combined density of you and the jacket below that of water.

Which physical principle is demonstrated by hydraulic lifts and presses?

Pascal’s principle.

In a hydraulic press, what quantity can never exceed the input value?

Energy output can never exceed energy input.

Does the air in a classroom have mass, weight, and energy?

Yes—air possesses all three.

What happens to marshmallows placed in a vacuum chamber?

They expand and become larger.

If a gas is compressed to half its original volume at constant temperature, what happens to its pressure?

The pressure doubles (Boyle’s Law).

Archimedes’ principle applies to which states of matter?

All fluids—both liquids and gases.

The buoyant force of air on an object equals the displaced by the object.

Weight of the air displaced.

Which objects experience a buoyant force in air?

All objects, including gas-filled balloons and people.

How does the pressure inside an inflated, stretched balloon compare with outside air pressure?

It is greater inside the balloon.

Why can an umbrella lift upward on a windy day?

Wind reduces air pressure over the curved top surface (Bernoulli effect).

Which type of molecular motion is most directly related to temperature?

Translational kinetic motion of molecules.

Temperature is most closely tied to the average molecular energy.

Kinetic energy.

Which two temperature scales use equal-sized degrees?

Celsius and Kelvin.

Which common temperature scale has the smallest degree interval?

Fahrenheit.

How much energy raises 1 gram of water by 1 °C?

4.19 joules (1 calorie).

When a ‘C’-shaped metal ring is heated, what happens to the width of its gap?

The gap widens.

A thermometer "takes its own temperature" because of what thermal principle?

Thermal equilibrium (Zeroth Law of Thermodynamics).

Which is hotter: boiling tea in a cup or in a large pail?

Both are at the same temperature (100 °C at standard pressure).

Cooling 10 g of water by 1 °C releases how much heat?

41.9 joules.

Heat energy naturally flows from an object of higher to one of lower .

Temperature; temperature.

Mixing 1 L of 40 °C water with 1 L of 20 °C water yields a final temperature of about .

30 °C.

When an iron ring is heated, does the hole inside get larger or smaller?

Larger—everything expands uniformly, including the hole.

The heat transferred by a substance depends on its mass, temperature change, and .

Specific heat capacity.

Water is densest at 4 °C. To make 4 °C water expand, should you raise or lower its temperature slightly?

Either raising or lowering the temperature causes expansion.

Water pipes burst in freezing weather mainly because

Water expands when it freezes.

Equal masses of aluminum and copper wire are placed in a flame. Which heats up faster?

Copper, because it has a lower specific heat capacity.

Island climates are moderate largely because of water’s .

High specific heat capacity.

When you touch ice, in which direction does energy (heat) flow?

From your finger to the ice.

Heating a sealed can of air increases the air’s .

Temperature (mass remains constant).

Between 0 °C and 4 °C, warming water slightly makes it .

Contract until it reaches maximum density at 4 °C.

For equal temperature changes, which state of matter generally expands the most?

Gases.

As a metal plate with a hole cools, the diameter of the hole .

Decreases (contracts).

The deep bottom water of Lake Tahoe always remains at approximately .

4 °C (temperature of maximum-density water).

A heated bimetallic strip bends toward its iron side because

Copper expands more than iron.

Which is larger: one Kelvin or one Celsius degree?

They are the same size.

What is the lowest possible temperature in nature?

−273 °C (0 K, absolute zero).

Why does the temperature of an ice-water mixture stay at 0 °C as long as ice is present?

The absorbed heat is used as latent heat to melt the ice rather than to raise the temperature.

Name the three common phases of matter.

Solid, liquid, and gas (vapor).

What do we call the heat required to melt a specific amount of a solid at its melting point?

Heat of fusion (a type of latent heat).

At what temperature does pure water melt and freeze at 1 atm pressure?

0 °C.

What happens to temperature during a phase change at constant pressure?

It remains constant until the transition is complete.

What is sublimation? Give an example.

Direct change from solid to gas; e.g., solid naphthalene (moth balls) turning into vapor.

What is the reverse process of sublimation?

Deposition (gas directly to solid).

Define heat of crystallization.

Heat released when a specific amount of liquid solidifies at a given temperature; numerically equal to the heat of fusion.

Does melting increase or decrease the order of particles?

It decreases their order (from orderly crystal lattice to less-ordered liquid).

Is vaporization a cooling or warming process for the remaining liquid?

Cooling, because high-energy molecules leave, lowering the average kinetic energy.

State the main difference between evaporation and vaporization (boiling).

Evaporation is slow and surface-only; vaporization is rapid and occurs throughout the liquid with bubble formation.

Why does evaporation cool a liquid?

Fast, high-energy molecules escape, leaving behind slower ones and reducing average kinetic energy and temperature.

What is the heat of vaporization?

Heat required to convert a specific amount of liquid to vapor at a given temperature.

What is the heat of condensation and how does it compare with heat of vaporization?

Heat released when vapor becomes liquid; equal in magnitude but opposite in sign to the heat of vaporization.

Is condensation a warming or cooling process for the surroundings?

Warming, because it releases heat.

What term describes the heat needed to change the phase of 1 kg of a substance at constant temperature and pressure?

Latent heat.

In what units is latent heat usually expressed?

Joules per kilogram (J/kg) or calories per kilogram (cal/kg).

At what temperature does liquid water boil at 1 atm?

100 °C.

How much heat is required to melt 2 kg of ice at 0 °C? (Latent heat of fusion = 33.5 × 10⁴ J/kg)

6.7 × 10⁵ J.

During condensation, what happens to the kinetic energy of gas molecules that strike the liquid surface?

It is transferred to the liquid, increasing its temperature (warming effect).

What general rule relates energy changes to order during phase transitions?

Changes toward a more random state absorb energy; changes toward a more ordered state release energy.