Which heat transfer mechanism is responsible for heating a pan on a stove?
A Evaporation
B Radiation
C Convection
D Conduction
Conduction is the process by which heat is transferred directly through a material, from a hotter area to a cooler one. When a pan is placed on a stove, heat is transferred from the stove burner through the pan by conduction.
What is the primary factor that affects the rate of heat transfer by conduction?
A Material thickness
B Temperature difference
C Surface roughness
D Fluid temperature
The rate of heat transfer by conduction is inversely proportional to the thickness of the material. A thicker material resists heat flow more, thus reducing the heat transfer rate. The temperature difference also plays a role, but material thickness is crucial.
What is the primary characteristic of heat transfer by radiation?
A Requires a medium
B Relies on temperature difference
C Involves electromagnetic waves
D Involves phase changes
Radiation transfers heat through electromagnetic waves, and unlike conduction and convection, it does not require a medium. Heat from the Sun, for example, travels to Earth through radiation, without the need for air or another material.
Which of the following factors influences the rate of convective heat transfer?
A Emissivity
B Fluid velocity
C Material density
D Fluid temperature
In convection, the rate of heat transfer is influenced by the fluid velocity. A higher velocity allows the fluid to carry heat more effectively from the heated surface to cooler regions, increasing the overall heat transfer rate.
How does increasing the surface area of a material affect its heat transfer rate?
A Decreases heat transfer
B Reduces thermal resistance
C Increases heat transfer
D No effect
Increasing the surface area allows more space for heat to be transferred between the material and the surrounding fluid or medium. This improves the efficiency of heat exchange by enhancing conduction, convection, or radiation.
What is the effect of the temperature gradient on heat transfer?
A Increases heat transfer
B Decreases heat transfer
C Changes material properties
D No effect
The temperature gradient (difference in temperature between two points) drives heat transfer. A larger temperature difference results in a faster rate of heat transfer, whether through conduction, convection, or radiation, according to the governing laws.
Which of the following is a common material used to increase heat dissipation in heat sinks?
A Copper
B Steel
C Aluminum
D Plastic
Aluminum is widely used in heat sinks due to its high thermal conductivity and lightweight nature. It efficiently conducts heat away from electronic components, ensuring they stay cool and function optimally.
What type of heat transfer occurs in a fluid flowing over a hot surface?
A Radiation
B Convection
C Freezing
D Conduction
Convection is the mode of heat transfer in fluids. When a fluid flows over a hot surface, it transfers heat from the surface to the fluid. The heated fluid then rises, and cooler fluid moves in to take its place, continuing the heat transfer process.
What is the primary factor that affects the efficiency of a heat exchanger?
A Fluid velocity
B Material thickness
C Surface area
D Heat capacity
The efficiency of a heat exchanger depends heavily on its surface area. A larger surface area allows for more contact between the hot and cold fluids, enhancing heat transfer between them and improving the overall efficiency.
In which heat transfer process does the phase change occur at a constant temperature?
A Conduction
B Radiation
C Convection
D Condensation
During condensation, a gas turns into a liquid, and this process occurs at a constant temperature. The heat released during condensation is known as latent heat, and this energy is transferred to the surroundings.
Which of the following is a key assumption in Fourier’s Law of heat conduction?
A Steady-state conditions
B Transient conditions
C Non-uniform material properties
D Variable temperature
Fourier’s Law assumes steady-state conditions, meaning the temperature at each point remains constant over time. It describes how heat is conducted through a material when there is a constant temperature gradient.
What is the effect of reducing the thermal conductivity of a material?
A Increases heat transfer
B Decreases heat transfer
C Increases thermal efficiency
D No effect
Reducing the thermal conductivity of a material decreases its ability to transfer heat. Materials with low thermal conductivity are used as insulators to reduce heat flow and improve energy efficiency.
Which of the following is a type of insulation material commonly used in thermal systems?
A Concrete
B Copper
C Styrofoam
D Steel
Styrofoam is a common insulation material because it has low thermal conductivity, preventing heat transfer. It is used in various thermal systems to reduce heat loss or gain, especially in buildings and refrigeration units.
What does the term “latent heat” refer to?
A Heat required to change temperature
B Heat lost to surroundings
C Heat transferred by radiation
D Heat required for a phase change
Latent heat refers to the amount of heat required for a substance to change its phase, such as from solid to liquid (melting) or from liquid to gas (boiling), without changing its temperature during the transition.
What does thermal efficiency of a heat engine depend on?
A Heat source temperature
B Engine speed
C Heat transfer rate
D Fluid properties
The thermal efficiency of a heat engine is largely determined by the temperature of the heat source. According to the Carnot efficiency formula, the higher the source temperature, the higher the possible efficiency of the engine.