Question 1

The thermal conductivity of copper is 397 J/s⋅m⋅°C and of silver is 427 J/s⋅m⋅°C.A rod of each material is used as a heat conductor.If the rods have the same geometry and are used between the same temperature differences for the same time interval,what is the ratio of the heat transferred by copper to the heat transferred by the silver?

Accepted Answer

The heat transferred ($Q$) through a material is directly proportional to its thermal conductivity ($k$), given by the equation $Q = kA(T_2 - T_1)t/L$, where $A$ is the cross-sectional area, $T_2 - T_1$ is the temperature difference, $t$ is the time, and $L$ is the length of the material. Since all other factors are the same for both materials, the ratio of heat transferred by copper to that by silver is simply the ratio of their thermal conductivities: $397/427 = 0.930$.

Question 2

The emissivity of an ideal reflector has which of the following values?

Accepted Answer

An ideal reflector does not absorb any radiation but reflects all incident radiation. Therefore, its emissivity, which measures its effectiveness in emitting thermal radiation, is 0.

Question 3

Which one of the following processes of heat transfer requires the presence of a fluid?

Accepted Answer

Convection is the process of heat transfer that requires the presence of a fluid. In convection, heat is transferred through the movement of a fluid or gas, such as the rising of warm air or the circulating of heated water. Conduction and radiation can occur without the presence of a fluid.

Question 4

An object at 30.0°C has its temperature increased to 41.0°C.The power then radiated by this object increases by how many percent?

Accepted Answer

The power radiated by an object is given by the Stefan-Boltzmann law: 
P = εσAT⁴
where P is power, ε is the emissivity (assumed to be 1 for simplicity), σ is the Stefan-Boltzmann constant, A is the surface area, and T is the temperature in Kelvin. 
The ratio of the powers (P2/P1) can be written as: 
P2/P1 = (T2/T1)⁴
where T1 and T2 are the initial and final temperatures in Kelvin. 
Using this formula, we can find the ratio of the powers for the given temperatures: 
P2/P1 = (314/303)⁴ = 1.153 
This means that the power is increased by 15.3% (100% x 0.153) when the temperature is increased from 30°C to 41°C. Therefore, the answer is (B).

Question 5

The filament temperature of a light bulb is 2 100 K when the bulb delivers 40.0 W of power.If its emissivity remains constant,what power is delivered when the filament temperature is 2 500 K?

Accepted Answer

The answer of The filament temperature of a light bulb...

Question 6

Consider two different rods.The greatest thermal conductivity will be in the rod with

Accepted Answer

The greatest thermal conductivity occurs when there are more free electrons available to move and transfer heat energy from atom to atom. Therefore, the rod with electrons that are freer to move from atom to atom will have the greater thermal conductivity.

Question 7

At high noon,the Sun delivers 990 W to each square meter of a blacktop road.What is the equilibrium temperature of the hot asphalt,assuming its emissivity e = 1? (σ = 5.67 × 10−⁸ W/m²⋅K⁴).

Accepted Answer

The equilibrium temperature of the asphalt can be found using the Stefan-Boltzmann law, which relates the power radiated per unit area of a black body to its temperature. The formula is $P = \sigma e T^4$, where $P$ is the power per unit area, $\sigma$ is the Stefan-Boltzmann constant ($5.67 \times 10^{-8} \, \text{W/m}^2\cdot\text{K}^4$), $e$ is the emissivity, and $T$ is the temperature in Kelvin.Given that the Sun delivers 990 W/m^2 and assuming the emissivity $e = 1$, we can set $P = 990 \, \text{W/m}^2$ and solve for $T$:$$990 = 5.67 \times 10^{-8} \times 1 \times T^4$$Solving for $T$ gives:$$T = \left(\frac{990}{5.67 \times 10^{-8}}\right)^{1/4}$$$$T \approx 364.5 \, \text{K}$$To convert to Celsius, subtract 273.15:$$364.5 \, \text{K} - 273.15 = 91.35 \, ^\circ\text{C}$$Rounding to the nearest option gives 90.5°C.

Question 8

If one's hands are being warmed by holding them to one side of a flame,the predominant form of heat transfer is what process?

Accepted Answer

Radiation is the process by which heat is transferred by electromagnetic waves without requiring any medium. In this case, the heat from the fire is transferred to the hands through radiation. Conduction involves the transfer of heat through a medium or from one object to another in direct contact, but in this case, there is no direct contact between the hands and the fire. Convection involves the transfer of heat through the movement of heated fluids or gases, but again, there is no fluid or gas involved in this scenario. Vaporization involves the phase change from liquid to gas, and is not applicable in this case.

Question 9

In winter,light-colored clothes will keep you warmer than dark-colored clothes if

Accepted Answer

The answer of In winter,light-colored clothes will keep you warmer...

Question 10

If cooking is done using an aluminum pan over an electric burner,which of the following will not promote the rate of heat flow from burner to food?

Accepted Answer

Increasing the thickness of the pan bottom would actually reduce the rate of heat flow from the burner to the food because thicker materials tend to have higher thermal resistance, making it harder for heat to pass through quickly.

Question 11

The surface of the Sun has a temperature of about 5 770 K.If the radius of the Sun is 7 × 10⁸ m,determine the power output of the Sun.(Take e = 1,and σ = 5.67 × 10−⁸ W/m²⋅K⁴).

Accepted Answer

The power output of the Sun can be calculated using the Stefan-Boltzmann law: $P = 4\pi R^2 \sigma T^4$, where $R$ is the radius of the Sun, $\sigma$ is the Stefan-Boltzmann constant, and $T$ is the temperature. Substituting the given values: $P = 4\pi (7 \times 10^{8})^2 (5.67 \times 10^{-8}) (5770)^4$, results in approximately $3.9 \times 10^{26}$ W.

Question 12

The use of fiberglass insulation in the outer walls of a building is intended to minimize heat transfer through the wall by what process?

Accepted Answer

Fiberglass insulation reduces the rate of heat transfer through the outer walls of a building by minimizing conduction, which involves the transfer of heat through a material. The fiberglass material itself does not conduct heat well and serves as a barrier to heat transfer. Radiation and convection are not directly affected by the use of insulation, while vaporization is not a primary mode of heat transfer in this context.

Question 13

Which type of heating causes sunburn?

Accepted Answer

Radiation is the type of heating that causes sunburn, as it involves the transfer of energy through waves without requiring a medium for the heat to travel through. Conduction and convection both require a medium to transfer heat, and do not typically result in sunburn.

Question 14

A silver bar of length 25.0 cm and cross-sectional area 1.25 cm² is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice.How much ice is melted per second? (For silver,k = 427 J/s⋅m⋅°C.For ice,L_f = 334 000 J/kg. )

Accepted Answer

The answer of A silver bar of length 25.0 cm...

Question 15

A windowpane is half a centimeter thick and has an area of 1.10 m².The temperature difference between the inside and outside surfaces of the pane is 19.0 °C.What is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C. )

Accepted Answer

The answer of A windowpane is half a centimeter thick...

Question 16

The tungsten filament of a light bulb has an operating temperature of about 2 050 K.If the emitting area of the filament is 0.70 cm²,and its emissivity is 0.68,what is the power output of the light bulb? (σ = 5.67 × 10−⁸ W/m²⋅K⁴)

Accepted Answer

The power output can be calculated using the Stefan-Boltzmann law: P = εσAT⁴. Convert the area from cm² to m², then substitute the values: P = 0.68 * 5.67 × 10⁻⁸ W/m²⋅K⁴ * 0.70 × 10⁻⁴ m² * (2050 K)⁴ ≈ 47.7 W.

Question 17

The surfaces of a Dewar flask are silvered for the purpose of minimizing heat transfer by what process?

Accepted Answer

The silvered surface of a Dewar flask is designed to reduce heat transfer by radiation. The shiny surface reflects thermal radiation, which helps to reduce the amount of heat that is lost or gained through the walls of the flask. Conduction and convection can also contribute to heat transfer, but these processes are minimized through the use of a vacuum layer between the inner and outer walls of the Dewar flask. Vaporization is not a relevant process for heat transfer in a Dewar flask.

Question 18

A 1.9-m² Thermopane window is constructed by using two layers of glass 4.0 mm thick,separated by an air space of 5.0 mm.If the temperature difference is 25.0 °C from the inside of the house to the outside air,what is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C and for air 0.023 4 J/s⋅m⋅°C. )

Accepted Answer

The answer of A 1.9-m² Thermopane window is constructed by...

Question 19

When a wool blanket is used to keep warm,what is the primary insulating material?

Accepted Answer

Air is considered the primary insulating material in a wool blanket. Wool fibers trap air within them, creating pockets of insulation that help to retain body heat. The trim around the edge of the blanket and a thin layer of aluminum foil inside the blanket are not typically used as insulating materials in wool blankets.

Question 20

How does the heat energy from the Sun reach us through the vacuum of space?

Accepted Answer

Heat energy from the Sun reaches us through radiation, as there is no medium for conduction or convection to occur in the vacuum of space. The Sun emits electromagnetic radiation, which travels through space until it reaches the Earth, where it is absorbed, reflected or scattered by the atmosphere and ultimately heats the surface.

Quiz 11: Energy in Thermal Processes

The emissivity of an ideal reflector has which of the following values?

Which one of the following processes of heat transfer requires the presence of a fluid?

An object at 30.0°C has its temperature increased to 41.0°C.The power then radiated by this object increases by how many percent?

The filament temperature of a light bulb is 2 100 K when the bulb delivers 40.0 W of power.If its emissivity remains constant,what power is delivered when the filament temperature is 2 500 K?

Consider two different rods.The greatest thermal conductivity will be in the rod with

At high noon,the Sun delivers 990 W to each square meter of a blacktop road.What is the equilibrium temperature of the hot asphalt,assuming its emissivity e = 1? (σ = 5.67 × 10−⁸ W/m²⋅K⁴) .

If one's hands are being warmed by holding them to one side of a flame,the predominant form of heat transfer is what process?

In winter,light-colored clothes will keep you warmer than dark-colored clothes if

If cooking is done using an aluminum pan over an electric burner,which of the following will not promote the rate of heat flow from burner to food?

The surface of the Sun has a temperature of about 5 770 K.If the radius of the Sun is 7 × 10⁸ m,determine the power output of the Sun.(Take e = 1,and σ = 5.67 × 10−⁸ W/m²⋅K⁴) .

The use of fiberglass insulation in the outer walls of a building is intended to minimize heat transfer through the wall by what process?

Which type of heating causes sunburn?

A silver bar of length 25.0 cm and cross-sectional area 1.25 cm² is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice.How much ice is melted per second? (For silver,k = 427 J/s⋅m⋅°C.For ice,L_f = 334 000 J/kg. )

A windowpane is half a centimeter thick and has an area of 1.10 m².The temperature difference between the inside and outside surfaces of the pane is 19.0 °C.What is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C. )

The tungsten filament of a light bulb has an operating temperature of about 2 050 K.If the emitting area of the filament is 0.70 cm²,and its emissivity is 0.68,what is the power output of the light bulb? (σ = 5.67 × 10−⁸ W/m²⋅K⁴)

The surfaces of a Dewar flask are silvered for the purpose of minimizing heat transfer by what process?

When a wool blanket is used to keep warm,what is the primary insulating material?

How does the heat energy from the Sun reach us through the vacuum of space?

Quiz 11: Energy in Thermal Processes

The emissivity of an ideal reflector has which of the following values?

Which one of the following processes of heat transfer requires the presence of a fluid?

An object at 30.0°C has its temperature increased to 41.0°C.The power then radiated by this object increases by how many percent?

The filament temperature of a light bulb is 2 100 K when the bulb delivers 40.0 W of power.If its emissivity remains constant,what power is delivered when the filament temperature is 2 500 K?

Consider two different rods.The greatest thermal conductivity will be in the rod with

At high noon,the Sun delivers 990 W to each square meter of a blacktop road.What is the equilibrium temperature of the hot asphalt,assuming its emissivity e = 1? (σ = 5.67 × 10−8 W/m2⋅K4) .

If one's hands are being warmed by holding them to one side of a flame,the predominant form of heat transfer is what process?

In winter,light-colored clothes will keep you warmer than dark-colored clothes if

If cooking is done using an aluminum pan over an electric burner,which of the following will not promote the rate of heat flow from burner to food?

The surface of the Sun has a temperature of about 5 770 K.If the radius of the Sun is 7 × 108 m,determine the power output of the Sun.(Take e = 1,and σ = 5.67 × 10−8 W/m2⋅K4) .

The use of fiberglass insulation in the outer walls of a building is intended to minimize heat transfer through the wall by what process?

Which type of heating causes sunburn?

A silver bar of length 25.0 cm and cross-sectional area 1.25 cm2 is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice.How much ice is melted per second? (For silver,k = 427 J/s⋅m⋅°C.For ice,Lf = 334 000 J/kg. )

A windowpane is half a centimeter thick and has an area of 1.10 m2.The temperature difference between the inside and outside surfaces of the pane is 19.0 °C.What is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C. )

The tungsten filament of a light bulb has an operating temperature of about 2 050 K.If the emitting area of the filament is 0.70 cm2,and its emissivity is 0.68,what is the power output of the light bulb? (σ = 5.67 × 10−8 W/m2⋅K4)

The surfaces of a Dewar flask are silvered for the purpose of minimizing heat transfer by what process?

When a wool blanket is used to keep warm,what is the primary insulating material?

How does the heat energy from the Sun reach us through the vacuum of space?

At high noon,the Sun delivers 990 W to each square meter of a blacktop road.What is the equilibrium temperature of the hot asphalt,assuming its emissivity e = 1? (σ = 5.67 × 10−⁸ W/m²⋅K⁴) .

The surface of the Sun has a temperature of about 5 770 K.If the radius of the Sun is 7 × 10⁸ m,determine the power output of the Sun.(Take e = 1,and σ = 5.67 × 10−⁸ W/m²⋅K⁴) .

A silver bar of length 25.0 cm and cross-sectional area 1.25 cm² is used to transfer heat from a 80.5°C reservoir to a 0°C block of ice.How much ice is melted per second? (For silver,k = 427 J/s⋅m⋅°C.For ice,L_f = 334 000 J/kg. )

A windowpane is half a centimeter thick and has an area of 1.10 m².The temperature difference between the inside and outside surfaces of the pane is 19.0 °C.What is the rate of heat flow through this window? (Thermal conductivity for glass is 0.840 J/s⋅m⋅°C. )

The tungsten filament of a light bulb has an operating temperature of about 2 050 K.If the emitting area of the filament is 0.70 cm²,and its emissivity is 0.68,what is the power output of the light bulb? (σ = 5.67 × 10−⁸ W/m²⋅K⁴)