Chapter 16: Heat Transfer

The correct answer is low thermal conductivity of the coals. This means that the coals do not transfer heat efficiently to the feet, allowing one to walk on them without getting burned. The low thermal conductivity of the coals prevents a significant amount of heat from reaching the feet, reducing the risk of burns.

A good heat conductor is a poor insulator because a material that is able to conduct heat well allows heat to easily flow through it. On the other hand, a poor insulator does not impede the flow of heat and allows it to transfer easily. Therefore, a good heat conductor is not a good insulator as it does not effectively resist the transfer of heat.

Black surfaces are known to absorb more sunlight compared to white surfaces. This is because black surfaces have a higher absorption rate for all wavelengths of light, including visible and infrared light. As a result, black surfaces become warmer when exposed to sunlight. In contrast, white surfaces reflect most of the sunlight, leading to less absorption and a cooler temperature. Therefore, at the end of a sunny day, the black road surface will be warmer than the white surface.

A rug feels warmer on the feet compared to a tile floor because it is a better insulator than tile. Insulators are materials that do not conduct heat well, so they prevent heat transfer from the body to the floor. The rug traps more heat and creates a barrier, resulting in a warmer sensation on the feet.

Very light molecules move with greater speed in the air because they have less mass and therefore experience less resistance from the air. This allows them to move more quickly compared to heavier molecules, which have more mass and experience more resistance. The concept of kinetic theory of gases states that at the same temperature, all molecules have the same average kinetic energy. Since kinetic energy is directly proportional to the square of the velocity, lighter molecules will have higher velocities and move faster in the air.

Substances can absorb heat energy through different processes. Conduction refers to the transfer of heat through direct contact between particles. Convection involves the transfer of heat through the movement of fluid or gas particles. Radiation is the transfer of heat through electromagnetic waves. Therefore, substances can absorb heat energy through all of these processes.

The pupil of the eye is a net absorber of radiant energy because it controls the amount of light that enters the eye. When there is a bright light, the pupil constricts, reducing the amount of light entering the eye. This is important to protect the retina from excessive light exposure and potential damage. Conversely, in dim light, the pupil dilates, allowing more light to enter the eye and improve vision. Therefore, the pupil acts as a net absorber, regulating the amount of radiant energy that reaches the retina.

The color of an object affects its ability to absorb and emit heat. Black objects absorb more heat compared to silver objects, which reflect heat. Therefore, a black pot will absorb heat from the surroundings more quickly, causing the cold water to warm up faster compared to a silver pot.

When an object's temperature is higher than its surroundings, it means that the object has a higher thermal energy compared to its surroundings. As a result, the object will radiate energy in the form of heat to its surroundings in order to achieve thermal equilibrium. This radiation of energy makes the object a net radiator of energy.

Newton's law of cooling states that the rate of cooling of an object is directly proportional to the temperature difference between the object and its surroundings. This means that the law applies to objects that are cooling, as the temperature difference between the object and its surroundings is decreasing. However, it also applies to objects that are heating, as the temperature difference between the object and its surroundings is increasing. Therefore, the correct answer is "both of these".

When a volume of air is compressed, its molecules are forced closer together, resulting in an increase in the average kinetic energy of the molecules. This increase in kinetic energy translates to an increase in temperature. Therefore, the correct answer is that the temperature of the compressed air increases.

An igloo would provide better insulation and retain heat more effectively compared to a tent, wooden house, or car. The compact and dome-shaped structure of an igloo helps to trap warm air inside and prevent cold air from entering. Additionally, the snow used to build an igloo acts as a natural insulator, further enhancing its ability to retain heat. In contrast, a tent, wooden house, or car would not provide the same level of insulation and would allow cold air to seep in, making it harder to stay warm in freezing weather.

When air molecules are heated, they gain energy and move faster, causing them to spread out and occupy more space. This increase in volume results in a decrease in density. Additionally, as air molecules rise and move to regions of lower pressure, they experience less force pushing down on them, allowing them to move more freely. Therefore, warm air rises due to both a decrease in density and a decrease in pressure.

As the temperature of an object increases, it emits more energy in the form of radiation. According to Wien's law, the wavelength of the radiation emitted by an object is inversely proportional to its temperature. This means that as the temperature increases, the wavelength of the radiation decreases, resulting in shorter wavelengths being emitted. Therefore, the statement "the shorter the wavelengths it radiates" is the correct answer.

The waves emitted by the sun and terrestrial wave emissions are the same in terms of their nature and characteristics, such as being electromagnetic waves. However, they differ in their frequencies and wavelengths. This means that while both types of waves share similarities, they have distinct properties that set them apart.

When a volume of air is warmed, it expands due to the increase in kinetic energy of its molecules. As the air expands, it moves away from other air molecules, causing a decrease in the overall temperature of the air. This is because the expansion of the air requires energy, which is obtained from the surrounding air, resulting in a cooling effect. Therefore, when a volume of air expands, it cools.

A black pot will cool a liter of hot water to room temperature faster because black absorbs and radiates heat more efficiently than other colors. The black pot will absorb more heat from the hot water, causing it to cool down faster. In contrast, a silver or red pot will reflect more heat, resulting in slower cooling. The size of the pot does play a role, but the color has a more significant impact on the rate of cooling.

The answer "supports this common knowledge" is correct because Newton's law of cooling states that the rate at which an object cools is directly proportional to the temperature difference between the object and its surroundings. Therefore, if a can of beverage is placed in the coldest part of a refrigerator, where the temperature difference is greater, it will cool faster compared to if it was placed in a warmer part of the refrigerator. This aligns with the common knowledge that a can of beverage will cool faster in the coldest part of a refrigerator.

Both the Sun and the Earth glow with electromagnetic waves. The Sun emits a wide range of electromagnetic waves, including visible light, ultraviolet rays, and X-rays. This is due to the high temperatures and nuclear reactions happening in its core. The Earth, on the other hand, also emits electromagnetic waves, primarily in the form of thermal radiation. This is because all objects with a temperature above absolute zero emit electromagnetic radiation. Therefore, both the Sun and the Earth can be considered as sources of electromagnetic waves.

If air were a better conductor than it is, it would be able to transfer heat more efficiently. During nighttime, when the Earth loses heat to the atmosphere, the air would quickly conduct the heat away from the surface. This would result in a faster cooling process and make the Earth considerably colder.

Convection is a mode of heat transfer where energy is transferred through the movement of fluids. It occurs when warmer fluid rises and cooler fluid sinks, creating a circulation pattern. While convection can occur in solids, liquids, and gases, the given answer "fluids" is the most accurate as it encompasses all three states of matter. Therefore, energy transfer by convection is primarily restricted to fluids.

Metals are good heat and electrical conductors because of the looseness of outer electrons in metal atoms. In metals, the outermost electrons are not strongly bound to the nucleus and are free to move throughout the metal lattice. This allows for the easy flow of both heat and electricity. When heat is applied to a metal, the loose electrons gain energy and move more rapidly, transferring the energy throughout the material. Similarly, when an electric potential is applied, the free electrons can easily move and carry the electric charge. Therefore, the looseness of outer electrons in metal atoms enables metals to conduct both heat and electricity effectively.

The correct answer is the white surface. Both black and white road surfaces radiate energy, but the black surface absorbs more energy from the sun during the day, making it warmer. At the end of a starry night, when there is no additional energy input from the sun, the black surface will cool down faster than the white surface, resulting in the white surface being warmer. This is because the white surface reflects more of the energy it receives, while the black surface absorbs more of it.

Adding cream to the coffee right away would help retain its heat for a longer period of time. The cream acts as an insulator, preventing the coffee from losing heat quickly. By adding cream immediately, the coffee will stay hotter for a longer duration, ensuring that it is still hot when you are ready to drink it.

Objects that radiate relatively well are typically good absorbers of radiation. When an object absorbs radiation, it converts the energy of the radiation into internal energy, increasing its temperature. This increase in temperature causes the object to radiate energy back into its surroundings. Therefore, objects that absorb radiation relatively well also tend to radiate energy effectively.

Hydrogen gas molecules have the greatest average speed in the mixture because they are the lightest gas molecules. According to Graham's law of effusion, the rate of effusion (and therefore the average speed) of a gas is inversely proportional to the square root of its molar mass. Since hydrogen has the lowest molar mass among the three gases, its molecules will have the highest average speed.

The planet Earth loses heat mainly by radiation. Radiation is the transfer of heat energy through electromagnetic waves. In the case of Earth, heat is radiated from the surface into the atmosphere and outer space. While conduction and convection also play a role in heat transfer, they are not the primary methods by which Earth loses heat. Conduction occurs when heat is transferred through direct contact, while convection involves the movement of heated fluids. However, radiation is the dominant process in the Earth's heat loss.

A good reflector of radiation is a poor absorber of radiation because when radiation hits a good reflector, it is mostly reflected back rather than being absorbed. This means that the material does not absorb much of the radiation that it is exposed to. Instead, it reflects the radiation away, making it a poor absorber.

A good absorber of radiation is a good emitter of radiation because when an object absorbs radiation, it gains energy. This energy is then re-emitted by the object in the form of radiation. Therefore, an object that efficiently absorbs radiation will also efficiently emit radiation, making it a good emitter.

The paper cup does not catch fire when held in a flame because the paper cup cannot become significantly hotter than the water it contains. This is because water has a high specific heat capacity, meaning it requires a large amount of heat to raise its temperature. As the flame heats the cup, the water inside absorbs the heat, preventing the cup from reaching a temperature high enough to ignite.

If an object is a poor absorber of radiation, it means that it does not absorb much radiation from its surroundings. However, if it is a good emitter of radiation, it means that it can emit radiation efficiently. This combination implies that the object is not able to absorb much heat from its surroundings, but it can emit heat effectively. As a result, its temperature would be less than its surroundings because it cannot absorb enough heat to reach the same temperature as its surroundings and instead loses heat through emission.

The statement "neither the Sun or the Earth awaits the next century" implies that both the Sun and the Earth will not be present in the future. The correct answer "already exists" suggests that the Sun and the Earth are already in existence and will not be waiting for the next century because they are already here.

When leaving the cool house for a short period on a hot day, it is more energy-efficient to turn off the air conditioner altogether. This is because leaving it on, even at a lower temperature setting, would still consume unnecessary energy to maintain the cool temperature in the empty house. By turning it off completely, energy is saved as the air conditioner does not need to work to cool an unoccupied space.

When leaving a warm house on a cold day for a short period of time, it is more energy-efficient to turn the thermostat down. This is because lowering the thermostat reduces the amount of energy needed to maintain the warm temperature while you are away. By lowering the thermostat, the heating system will consume less energy and therefore save energy during your absence.

The silver coating on the glass surfaces of a Thermos bottle reduces the energy that is transferred by radiation. Radiation is the transfer of heat through electromagnetic waves, and the silver coating reflects these waves back into the bottle, preventing them from escaping. This helps to keep the contents of the Thermos bottle hot or cold for longer periods of time. Conduction refers to the transfer of heat through direct contact, convection involves the transfer of heat through the movement of fluids, and friction does not play a significant role in heat transfer in this context.

When the hydrogen and oxygen molecules in a gas sample have the same temperature, it means that they have the same average kinetic energy. However, since the hydrogen molecules have a lower mass than the oxygen molecules, they will have a higher average speed. This is because kinetic energy is directly proportional to the square of the speed, so even though the hydrogen molecules have the same kinetic energy as the oxygen molecules, they will have a higher speed. Therefore, the correct answer is "kinetic energy, but more speed."

The sun's radiant energy is of shorter wavelengths than the Earth's because it has a higher temperature than the Earth. Temperature is directly related to the average kinetic energy of particles, and higher temperatures result in higher kinetic energy and shorter wavelengths of radiation. The sun is a massive ball of hot gases that undergoes nuclear fusion, generating immense amounts of heat and light. On the other hand, the Earth primarily receives energy from the sun and does not have the same level of internal energy or temperature. Therefore, the sun's higher temperature is the reason for its shorter wavelength radiant energy compared to the Earth.

If molecules in a gas sample moved so they completely missed each other, it means that there would be no collisions between the molecules. Collisions between gas molecules are what cause energy transfer and therefore determine the temperature of the gas. Without any collisions, there would be no change in the average kinetic energy of the gas molecules, and thus the temperature would stay the same.

When the absolute temperature of helium gas is doubled, according to the kinetic theory of gases, the average speed of its molecules also increases. However, the relationship between temperature and average speed is not linear. As the temperature increases, the average speed of the gas molecules increases, but not by the same factor. Therefore, when the absolute temperature is doubled, the average speed of the helium gas molecules will increase, but it will be less than double.

When a solid object radiates more energy than it absorbs, it means that it is losing energy to its surroundings. This loss of energy leads to a decrease in the internal energy of the object. As internal energy is directly related to the temperature of an object, the decrease in internal energy also results in a decrease in temperature. Therefore, the correct answer is that the internal energy decreases.

The correct answer is "neither of these, because internal energy is not temperature." This is because the internal energy of an object is not dependent on its surroundings or temperature. Internal energy refers to the total energy of all the particles within an object, including kinetic and potential energy. It is a measure of the object's microscopic energy and can change due to various factors like heat transfer, work done, or changes in the object's state. Therefore, the internal energy of an object does not determine whether it will be a net radiator or absorber of energy.